We may, indeed, reduce the antagonism to a form comprehensive of all

cases, if we consider it as existing between the sums of the forces,

latent and active, used for the two purposes. The molecules which make

up a plant or animal, have been formed by the absorption of forces

directly or indirectly derived from the Sun; and hence the quantity

of matter raised to the form called organic, which a plant or animal

presents, is equivalent to a certain amount of force. Another amount of

force is expressed by the totality of its differentiations. A further

amount of force is that dissipated in its actions. And in these three

amounts added together, we have the whole expense of the individual

life. So, too, the whole expense of establishing each new individual

includes--first the forces latent in the substance composing it when

born or hatched; second the forces latent in the prepared nutriment

afterwards supplied; and third the forces expended in feeding and

protecting it. These two sets of forces being taken from a common fund,

it is manifest that either set can increase only by decrease of the

other. If, of the force which the parent obtains from the environment,

much is consumed in its own life, little remains to be consumed in

producing other lives; and, conversely, if there is a great consumption

in producing other lives, it can only be where comparatively little is

reserved for parental life.

Hence, then, Individuation and Genesis are necessarily antagonistic.

Grouping under the word Individuation all processes by which

individual life is completed and maintained; and enlarging the

meaning of the word Genesis so as to include all processes aiding

the formation and perfecting of new individuals; we see that the

two are fundamentally opposed. Assuming other things to remain the

same--assuming that environing conditions as to climate, food,

enemies, &c., continue constant; then, inevitably, every higher

degree of individual evolution is followed by a lower degree of

race-multiplication, and _vice versâ_. Progress in bulk, complexity, or

activity, involves retrogress in fertility; and progress in fertility

involves retrogress in bulk, complexity, or activity.

This statement needs a slight qualification. For reasons to be

hereafter assigned, the relation described is never completely

maintained; and in the small departure from it, we shall find a

remarkable self-acting tendency to further the supremacy of the most

developed types. Here, however, this hint must suffice: explanation

would carry us too far out of our line of argument. For the present

it will not lead us astray if we regard this inverse variation of

Individuation and Genesis as exact.

§ 328. Thus, then, the condition which each race must fulfil if it is

to survive, is a condition which, in the nature of things, it ever

tends to fulfil. In the last chapter we saw that a species cannot be

maintained unless the power to preserve individual life and the power

to propagate other individuals vary inversely. And here we have seen

that, irrespective of an end to be subserved, these powers cannot do

other than vary inversely. On the one hand, given a certain totality

of destroying forces with which the species has to contend; and in

proportion as its members have severally but small ability to resist

these forces, it is requisite that they should have great ability to

form new individuals, and _vice versâ_. On the other hand, given the

quantity of force, absorbed as food or otherwise, which the species

can use to counterbalance these destroying forces; and in proportion

as much of it is expended in preserving the individual, little of it

can be reserved for producing new individuals, and _vice versâ_. There

is thus complete accordance between the requirements considered under

each aspect. The two necessities correspond.

We might rest on these deductions and their several corollaries.

Without going further we might with safety assert the general truths

that, other things equal, advancing evolution must be accompanied

by declining fertility; and that, in the highest types, fertility

must still further decrease if evolution still further increases.

We might be sure that if, other things equal, the relations between

an organism and its environment become so changed as permanently

to diminish the difficulties of self-preservation, there will be a

permanent increase in the rate of multiplication; and, conversely, that

a decrease of fertility will result where altered circumstances make

self-preservation more laborious.

But we need not content ourselves with these _à priori_ inferences. If

they are true, there must be an agreement between them and the observed

facts. Let us see how far such an agreement is traceable.

CHAPTER IV.

DIFFICULTIES OF INDUCTIVE VERIFICATION.

§ 329. Were all species subject to the same kinds and amounts of

destructive forces, it would be easy, by comparing different species,

to test the inverse variation of Individuation and Genesis. Or if

either the power of self-preservation or the power of multiplication

were constant, there would be little difficulty in seeing how the

other changed as the destroying forces changed. But comparisons are

nearly always partially vitiated by some want of parity. Each factor,

besides being variable as a whole, is compounded of factors that are

severally variable. Not simply is the sum of the forces destructive of

race different in every case; and not simply are both sets of forces

preservative of race unlike in their totalities in every case; but

each is made up of actions that bear such changing proportions to one

another as to prevent any positive estimation of its amount.

Before dealing with the facts as well as we can, it will be best to

glance at the chief difficulties; so that we may see the kind of

verification which is alone possible.

§ 330. Either absolutely, or relatively to any species, every

environment differs more or less from every other.

There are the unlikenesses of media--air, water, earth, organic matter;

severally involving special resistances to movement, and special losses

of heat. There are the contrasts of climate: here great expenditure

for the maintenance of temperature is needed, and there very little;

in one zone an organism is supplied with abundant light all the year

round, and in another only for a few months; this region yields an

almost unfailing supply of water, while that entails the exertion of

travelling many miles every night for a draught.

Permanent differences in the natures and distributions of aliment

greatly interfere with the comparisons. The Swallow goes through more

exertion than the Sparrow in securing a given weight of food; but then

their foods are dissimilar in nutritive qualities. There is a want of

parallelism between the circumstances of those herbivores which live

where the plains are annually covered for a time with rich herbage, but

afterwards become parched up, and of those inhabiting more temperate

regions. Insects whose larvæ feed on an abundant plant, as do several

of the genus _Vanessa_ on the Nettle, have practically an environment

very unlike that of insects such as _Deilephila Euphorbiæ_, whose larvæ

feed on a comparatively rare plant--the Sea-Spurge.

Again, comparisons between creatures otherwise akin in their

constitutions and circumstances, are hindered by inequalities in their

relations to enemies. Two animals, of which one is predatory and has

no foes but parasites while the other is much pursued, cannot properly

be contrasted with a view to determining the influence of size or

complexity.

Without multiplying instances, it will be clear enough then that the

aggregate of destructive actions, positive and negative, which each

species has to contend with, is so undefinable in the amounts and kinds

of its components, that nothing beyond a vague idea of its relative

total can be formed.

§ 331. Besides these immense variations in the outer actions to

be counter-balanced, there are immense variations in the inner

actions required to counterbalance them. Even were species similarly

conditioned, self-preservation would require of them extremely unlike

expenditures of force.

The cost of locomotion increases in a greater ratio than the size. In

virtue of the law that the weights of animals increase as the cubes

of their dimensions, while their powers of bearing strains increase

only as the squares of their dimensions (§ 46), preservation of its

various attitudes requires a large animal to consume more substance in

proportion to its weight, than it requires a small animal to consume;

and there results, other things equal, a difficulty of self-maintenance

which augments in a more rapid ratio than the bulk. Nor must we

overlook the further complication, that among aquatic creatures the

variation of resistance of the medium tends to produce an opposite

effect.

Again, the heat-consumption is a changing element in the total expense

of self-preservation. Creatures which have temperatures scarcely

above that of the air or water, may, other things equal, accumulate

more surplus nutriment than creatures which have to keep their bodies

warm spite of the continual loss by radiation and conduction. This

difference of cost is modified by the presence or absence of natural

clothing; and it is also modified by unlikenesses of size. Here the

bulky animals have the advantage: small masses cooling more rapidly

than large ones.

Dissimilarities of attack and defence are also causes of variation

in the outlay for self-maintenance. A creature that has to hunt, as

compared with another that gets a sufficiency of prey by lying in wait,

or a creature that escapes by speed as compared with another that

escapes by concealment, obviously leads a life that is physiologically

more costly. Animals which protect themselves passively, as the

Hedge-hog by its spines or as the Skunk and the Musk-rat by their

intolerable odours, are relatively economical; and have the more vital

capital for other purposes.

Amplification is needless. These instances will show that anything

beyond very general conceptions of the individual expenditures in

different cases, cannot be reached.

§ 332. Still more entangled are we among qualifying considerations

when we contrast species in their powers of multiplication. The total

cost of Genesis admits of even less definite estimation than does the

total cost of Individuation. I do not refer merely to the truth that

the degree of fertility depends on four factors--the age of commencing

reproduction, the number in each brood, the frequency of the broods,

and the time during which broods continue to be repeated. There are

many further obstacles in the way of comparisons.

Were all multiplication carried on sexually, the problem would be

less involved; but there are many kinds of asexual multiplication

alternating with the sexual. This asexual multiplication is in some

cases perpetual instead of occasional; and often has more forms than

one in the same species. The result is that we have to compare what

is here a periodic process with what is elsewhere a cyclical process

partly continuous and partly periodic: the calculation of fertility in

this last case being next to impossible.

We have to avoid being misled by the assumption that the cost of

Genesis is measured by the number of young produced, instead of being

measured, as it is, by the weight of nutriment abstracted to form

the young, _plus_ the weight consumed in caring for them. This total

weight may be very diversely apportioned. In contrast to the Cod with

its millions of small ova spawned without protection, we may put the

_Hippocampus_, or the Pipe-fish, with its few relatively-large ova

carried about by the male in a caudal pouch, or seated in hemispherical

pits in its skin; or we may put the still more remarkable genus

_Arius_, and especially _Arius Boakeii_--a fish some six or seven

inches long, which produces ten or a dozen eggs 5–10 mm. in diameter,

that are carried by the male in his mouth till they are hatched.

Here though the degrees of fertility, if measured by the numbers of

fertilized germs deposited, are extremely unlike, they are less unlike

if measured by the numbers of young which are hatched and survive long

enough to take care of themselves; nor will the tax on the parent-Cod

seem so immensely different from that on the parent-_Arius_, if the

masses of the ova, instead of their numbers, are compared. Again, while

sometimes the parental loss is little else but the matter deducted to

form eggs, &c., at other times it takes the shape of a small direct

deduction joined with a large indirect outlay. The Mason-wasp furnishes

a typical instance. In journeyings hither and thither to fetch bit

by bit the materials for building a cell; in putting together these

materials, as well as in secreting glutinous matter to act as cement;

and then, afterwards, in the labour of seeking for, and carrying, the

small caterpillars with which it fills up the cell to serve its larva

with food when it emerges from the egg; the Mason-wasp expends more

substance than is contained in the egg itself. And this supplementary

expenditure is manifestly so great that but few eggs can be housed and

provisioned.

Estimates of the cost of Genesis are further complicated by variations

in the ratio borne by the two sexes. Among Fishes the mass of milt

approaches in size the mass of spawn; but among higher _Vertebrata_

the substance lost by the one sex in the shape of sperm-cells is small

compared with that lost by the other sex in the shape of albumen

stored-up in the eggs, or blood supplied to the fœtus, or milk given

to the young. Then there come the differences of indirect tax on males

and females. While, frequently, the fostering of the young devolves

entirely on the female, occasionally the male undertakes it wholly or

in part. After building a nest, the male Stickleback guards the eggs

till they are hatched; as does also the great _Silurus glanis_ for some

forty days, during which he takes no food. And then, among most birds,

we have the male occupied in feeding the female during incubation,

and the young afterwards. Evidently all these differences affect the

proportion between the total cost of reproduction and the total cost of

individuation.

Whether the species is monogamous or polygamous, and whether there are

marked differences of size or of structure between males and females,

are also questions not to be overlooked. If there are many females to

one male, the total quantity of assimilated matter devoted by each

generation to the production of a new generation, is greater than if

there is a male to each female. Similarly, where the requirements

are such that small males will suffice, the larger quantity of food

left for the females makes possible a greater surplus available for

reproduction. Another cause has a like effect. Where the habits of the

race render it needless that both sexes should have developed powers of

locomotion--where, as in the Glow-worm and sundry _Lepidoptera_, the

female is wingless while the male has wings--the cost of Individuation

not being so great for the species as a whole, there arises a greater

reserve for Genesis: the matter which would otherwise have gone to the

production of wings and the using of them, may go to the production of

ova.

Other complications, as those which we see in Bees and Ants, might be

dwelt on; but the foregoing will amply serve the intended purpose.

§ 333. To ascertain by comparison of cases whether Individuation

and Genesis vary inversely, is thus an undertaking so beset with

difficulties, that we might despair of any satisfactory results,

were not the relation too marked a one to be hidden even by all

these complexities. Species are so extremely contrasted in their

degrees of evolution, and so extremely contrasted in their rates of

multiplication, that the law of relation between these traits becomes

unmistakable when the evidence is looked at in its _ensemble_. This we

shall soon find on ranging in order a number of typical cases.

In doing this it will be convenient to neglect, temporarily,

all unlikenesses among the circumstances in which organisms are

placed. At the outset, we will turn our attention wholly to the

antagonism displayed between the integrative process which results in

individual evolution and the disintegrative process which results in

multiplication of individuals; and this we will consider first as we

see it under the several forms of agamogenesis, and then as we see

it under the several forms of gamogenesis. We will next look at the

antagonism between propagation and that evolution which is shown by

increased complexity. And then we will consider the remaining phase of

the antagonism, as it exists between the degree of fertility and the

degree of evolution expressed by activity.

Afterwards, passing to the varying relations between organisms and

their environments, we will note how relative increase in the supply

of food, or relative decrease in the quantity of force expended by the

individual, entails relative increase in the quantity of force devoted

to multiplication, and _vice versâ_.

Certain minor qualifications, together with sundry important

corollaries, may then be entered upon.

CHAPTER V.

ANTAGONISM BETWEEN GROWTH AND ASEXUAL GENESIS.

§ 334. When illustrating, in Part IV, the morphological composition of

plants and animals, there were set down in groups, numerous facts which

we have here to look at from another point of view. Then we saw how,

by union of small simple aggregates, there are produced large compound

aggregates. Now we have to observe the reactive effect of this process

on the relative numbers of the aggregates. Our present subject is the

antagonism of Individuation and Genesis as seen under its simplest

form, in the self-evident truth that the same quantity of matter may

be divided into many small wholes or few large wholes; but that number

negatives largeness and largeness negatives number.

In setting down some examples we may conveniently adopt the same

arrangement as before. We will look at the facts as they are presented

by vegetal aggregates of the first order, of the second order, and of

the third order; and then as they are presented by animal aggregates of

the same three orders.

§ 335. The ordinary unicellular plants are at once microscopic and

enormously prolific. The often cited _Sphærella nivalis_, which shows

its immense powers of multiplication by reddening wide tracts of snow

in a single night, does this by developing in its cavity a brood of

young cells, which, being presently set free by the bursting of the

parent-cell, severally grow and quickly repeat the process. The like

occurs among sundry of those kindred forms of minute _Algæ_ which,

by their enormous numbers, sometimes suddenly change pools to an

opaque green. So, too, the _Desmidiaceæ_ often multiply so greatly as

to colour the water; and among the _Diatomaceæ_ the rate of genesis

by self-division, “is something really extraordinary. So soon as a

frustule is divided into two, each of the latter at once proceeds

with the act of self-division; so that, to use Professor Smith’s

approximative calculation of the possible rapidity of multiplication,

supposing the process to occupy, in any single instance, twenty-four

hours, ‘we should have, as the progeny of a single frustule, the

amazing number of one thousand millions in a single month.’” In these

cases the multiplication is so carried on that the parent is lost in

the offspring--the old individuality disappears either in the swarms of

zoospores it dissolves into, or in the two or four new individualities

simultaneously produced by fission. Vegetal aggregates of the first

order, have, however, a form of agamogenesis in which the parent

individuality is not lost: the young cells arise from the old cells

by external gemmation. This process, too, repeated as it is at short

intervals, results in immense fertility. The Yeast-fungus, which in a

few hours thus propagates itself throughout a large vat of wort, offers

a familiar example.

In certain compound forms that must be classed as plants of the second

order of aggregation, though very minute ones, self-division similarly

increases the numbers at high rates. The _Sarcina ventriculi_, a

parasitic plant which infests the stomach and swarms afresh as fast as

previous swarms are vomited, shows us a spontaneous fission of clusters

of cells. An allied mode of increase occurs in _Gonium pectorale:_

each cell of the cluster resolving itself into a secondary cluster,

and the secondary clusters then separating. “Supposing, which is very

probable, that a young _Gonium_ after twenty-four hours is capable of

development by fission, it follows that under favourable conditions

a single colony may on the second day develop 16, on the third 256,

on the fourth 4,096, and at the end of a week 268,435,456 other

organisms like itself.” In the _Volvocineæ_ this continual dissolution

of a primary compound individual into secondary compound individuals,

is carried on endogenously, and on a modified system: some only of

the component cells giving origin to young colonies, and the parent

bursting to liberate them. The numbers arising by this method also,

are sometimes so great as to tint large bodies of water. More fully

established and organized aggregates of the second order, such as the

higher Thallophytes and the lower Archegoniates, do not sacrifice

their individualities by fission; but nevertheless, by the kindred

process of gemmation, are continually hindered in the increase of their

individualities. The gemmæ called tetraspores are cast off in great

numbers by the marine _Algæ_. Among those simple _Jungermanniaceæ_

which consist of single fronds, the young ones that bud out grow for a

time in connexion with their parents, send rootlets from their under

sides into the soil, and presently separate themselves--a habit which

augments the number of individuals in proportion as it checks their

growths.

Plants of the third order of composition, arising by arrest of this

separation, exhibit a further corresponding decrease in the abundance

of the aggregates formed. Archegoniates of inferior types, in which

the axes produced by integration of fronds are but small and feeble,

are characterized by the habit of throwing off bulbils--bud-shaped

axes which, falling and taking root, add to the number of distinct

individuals. This agamic multiplication, very general among the

Mosses and their kindred, and not uncommon under a modified form

in such higher types as the Ferns, many of which produce young

ones from the surfaces of their fronds, becomes very unusual among

Phænogams. The detachment of bulbils, though not unknown among them,

is exceptional. And while it is true that some flowering plants, as

the Strawberry, multiply by a process allied to gemmation, yet this

is not characteristic of the class. A leading trait of these highest

groups, to which the largest members of the vegetal kingdom belong, is

that agamogenesis has so far ceased that it does not usually originate

independent plants. Though the axes which, budding one out of another,

compose a tree, are the equivalents of asexually-produced individuals;

yet the asexual production of them stops short of separation. These

vast integrations arise where spontaneous disintegration, and the

multiplication effected by it, have come to an end.

Thus, not forgetting that certain Phænogams, as _Begonia

phyllomaniaca_, revert to quite primitive modes of increase, we may

hold it as beyond question that while among the most minute plants

asexual multiplication is universal, and produces enormous numbers in

short periods, it becomes step by step more restricted in range and

frequency as we advance to large and compound plants; and disappears so

generally from the highest and largest, that its occurrence is regarded

as anomalous.

§ 336. Parallel examples furnished by animals make clear the purely

quantitative nature of this relation under its original form. Among

the _Protozoa_, as among the _Protophyta_, there occurs that process

by which the individuality of the parent is wholly lost in producing

offspring--the breaking up of the parental mass into a number of germs.

Some of the _Infusoria_, as for instance those of the genus _Kolpoda_

and several allied genera, become encysted and subsequently break

up into young ones. The more familiar mode of increase among these

animal-aggregates of the first order, by fission, though it sacrifices

the parent individuality by merging it in the individualities of the

two produced, sacrifices it less completely than does the dissolution

into a great number of germs. Occurring, however, as this fission does,

very frequently, and being completed, in some cases that have been

observed, in the course of half-an-hour, it results in immensely-rapid

multiplication. If all its offspring survive, and continue dividing

themselves, a single _Paramœcium_ is said to be capable of thus

originating 268 millions in the course of a month.[55] Nor is this

the greatest known rate of increase. Another animalcule, visible only

under a high magnifying power, “is calculated to generate 170 billions

in four days.”[56] And these enormous powers of propagation are

accompanied by a minuteness so extreme, that of some species one drop

of water would contain as many individuals as there are human beings on

the Earth! Even if we allow a large margin for exaggeration in these

estimates, it is beyond question that among these smallest of animals

the rate of asexual multiplication is immensely the greatest; and this

suffices for the purposes of argument.

Of animal aggregates belonging to the second order, that multiply

asexually with rapidity, the familiar Polypes furnish conspicuous

examples. By gemmation in most cases, in other cases by fission, and

in some cases by both, the agamogenesis is carried on among these

tribes. As shown in Fig. 148, the budding of young ones from the parent

_Hydra_ is carried on so actively, that before the oldest of them is

cast off half-a-dozen or more others have reached various stages of

growth; and even while still attached, the first-formed of the group

have commenced budding out from their sides a second generation of

young ones. In the _Hydra tuba_ this gemmiparous multiplication is

from time to time interrupted by a transverse splitting-up of the body

into segments, which successively separate and swim away: the result

of the two processes being that, in the course of a season, there are

produced from a single germ great numbers of young _Medusæ_, which

are the adult or sexual forms of the species. Respecting cœlenterate

animals of this degree of composition, it may be added that when we

ascend to the larger kinds we find asexual genesis far less active.

Though comparisons are interfered with by differences of structure and

mode of life, yet the contrasts are too striking to have their meanings

much obscured. If, for instance, we take a solitary _Actinozoon_ and

a solitary _Hydrozoon_, we see that the relatively-great bulk of the

first, goes along with a relatively-slow agamogenesis. The common

Sea-anemones are but occasionally observed to undergo self-division:

multiplication by budding being in some cases largely followed, but

their numbers are not rapidly increased by either process. A higher

class of secondary aggregates exemplifies the same general truth with

a difference. In the smaller members the agamogenesis is incomplete,

and in the larger it disappears. The gemmation of the minute _Polyzoa_,

though it does not end in the separation of the young individuals,

habitually goes to the extent of producing families of partially

independent individuals; but their near ally, the _Phoronis_, which

immensely exceeds them in size, is solitary and not gemmiparous. So,

too, is it with the _Ascidioida_. And then among the true _Mollusca_,

which are relatively large, no such thing is known as fission or

gemmation.

Take next the _Annulosa_, including under this title the _Annelida_

and _Arthropoda_. When treating of morphological composition, reasons

were given for the belief that the annulose animal is an aggregate of

the third order, the segments of which, produced one from another by

gemmation, originally became separate; but by progressive integration,

or arrested disintegration, there resulted a type in which many such

segments were permanently united (§§ 205–7 and note to § 207). Part

of the evidence there assigned, is evidence to be here repeated in

illustration of the direct antagonism of Growth and Asexual Genesis.

We saw how, among the lower Annelids, the string of segments produced

by gemmation presently divides transversely into two strings; and how,

in some cases, this resolution of the elongating string of segments

into groups that are to form separate individuals, goes on so actively

that as many as six groups are found in different stages of progress

to ultimate independence--a fact implying a high rate of fissiparous

multiplication.[57] Then we saw that, in the superior annulose types,

distinguished in the mass by including the larger species, fission

does not occur. The higher Annelids do not propagate in this way;

there is no known case of new individuals being so formed among the

_Myriapoda_; nor do the Crustaceans afford us a single instance of this

primordial mode of increase. It is, indeed, true that while articulate

animals never multiply asexually after this simplest method, and while

they are characterized in the mass by the cessation of agamogenesis

of every kind, there nevertheless occur in a few of their small

species, those higher forms of agamogenesis known as parthenogenesis

and pseudo-parthenogenesis; and that by these some of them multiply

very rapidly. Hereafter we shall find, in the interpretation of these

anomalies, further support for the general doctrine.

To the above evidence has to be added that which the _Vertebrata_

present. This may be very briefly summed up. On the one hand this

class, whether looked at in the aggregate or in its particular species,

immensely exceeds all other classes in the sizes of its individuals;

and on the other hand, agamogenesis under any form is absolutely

unknown in it. If it be said that budding occurs among the _Tunicata_

which, under the common title of _Chordata_, are included in the same

phylum with the _Vertebrata_, then it may firstly be replied that those

types which have no vertebræ cannot properly be called _Vertebrata_,

and secondly that if, as being _Chordata_, they must be recognized,

then the exception which they present further illustrates the truth

that agamogenetic multiplication occurs only in creatures small in

size, or low in structure, or both.

§ 337. Such are a few leading facts serving to show how deduction

is inductively verified, in so far as the antagonism between Growth

and Asexual Genesis is concerned. In whatever way we explain this

opposition of the integrative and disintegrative processes, the facts

and their implications remain the same. Indeed we need not commit

ourselves to any hypothesis respecting the physical causation. It

suffices to recognize the results under their most general aspects. We

cannot help admitting there are at work these two antagonist tendencies

to aggregation and separation; and we cannot help admitting that the

proportion between the aggregative and separative tendencies, must

in each case determine the relation between increase in bulk of the

individual and increase of the race in number.

The antithesis is as manifest _à posteriori_ as it is necessary _à

priori_. While the minutest organisms multiply asexually in their

billions; while the _Infusoria_ thus multiply in their millions;

while the small compound types next above them thus multiply in their

thousands; while larger and more compound types thus multiply in their

hundreds and their tens; the largest types do not thus multiply at all.

Conversely, those which do not multiply asexually at all, are a billion

or a million times the size of those which thus multiply with greatest

rapidity; and are a thousand times, or a hundred times, or ten times

the size of those which thus multiply with less and less rapidity.

Without saying that this inverse proportion is regular, which, as

we shall hereafter see, it cannot be, we may unhesitatingly assert

its average truth. That the smallest organisms habitually reproduce

asexually with immense rapidity; that the largest organisms never

reproduce at all in this manner; and that between these extremes there

is a general decrease of asexual reproduction along with an increase of

bulk; are propositions which admit of no dispute.

CHAPTER VI.

ANTAGONISM BETWEEN GROWTH AND SEXUAL GENESIS.

§ 338. In so far as it is a process of separation, sexual genesis is

like asexual genesis; and is therefore, equally with asexual genesis,

opposed to that aggregation which results in growth. Whether deduction

is made from one parent or from two, whether it is made from any part

of the body indifferently or from a specialized part, or whether it is

made directly or indirectly, it remains in any case a deduction; and in

proportion as it is great, or frequent, or both, it must restrain the

increase of the individual.

Here we have to group together the leading illustrations of this truth.

We will take them in the same order as before.

§ 339. The lowest vegetal forms, or rather, we may say, those forms

which we cannot class as either distinctly vegetal or distinctly

animal, show us a process of sexual multiplication that differs much

less from the asexual process than in the higher forms. The common

character which distinguishes sexual from asexual genesis, is that

the mass of protoplasm whence a new generation is to arise, has been

produced by the union of two portions of matter which were before more

widely separated. I use this general expression because, among the

simplest _Algæ_, this is not invariably matter supplied by different

individuals: certain _Diatomaceæ_ exhibit within a single cell, the

formation of a sporangium by a drawing together of the opposite halves

of the endochrome into a ball. Mostly, however, sporangia are products

of conjugation. The protoplasmic contents of two cells unite to form

the germ-mass or zygote; and these conjugating cells may be either

entirely independent, as in many _Desmidiaceæ_ and in the gametes of

many _Confervoideæ_; or they may be two of the adjacent cells forming

a thread, as in some _Conjugateæ_ and the gametes of _Confervoideæ_;

or they may be cells belonging to adjacent threads, as in other

_Conjugateæ_. But whether it is originated by a single parent-cell, or

by two parent-cells, the zygote, after remaining quiescent until there

recur the fit conditions for growth, either breaks up into a multitude

of spores, each of which produces an individual that usually multiplies

asexually, or germinates directly to produce one new individual;

and the fact here to be noted is, that as the entire contents of

the parent-cells unite to form the zygote, their individualities

are lost in the germs of a new generation. In these minute simple

types, sexual propagation just as completely sacrifices the life of

the parent or parents, as does that form of asexual propagation in

which the protoplasm resolves itself directly into zoospores. And in

the one case as in the other, this sacrifice is the concomitant of a

prodigious fertility. Slightly in advance of this, but still showing

us an almost equal loss of parental life in the lives of offspring,

is the process seen in such unicellular _Algæ_ as _Botrydium_, and

in minute _Fungi_ of the same degree of composition. These exhibit a

relatively-enormous development of the spore-producing part, and an

almost entire absorption of the parental substance into it. As evidence

of the resulting powers of multiplication, we have but to remember that

the spread of mould over stale food, the rapid destruction of crops

by mildew, and other kindred occurrences, are made possible by the

incalculably numerous spores thus generated and universally dispersed.

Plants a degree higher in composition supply a parallel series of

illustrations. We have among the larger _Fungi_, in which the

reproductive apparatus is relatively so enormous as to constitute

the ostensible plant, a similar subordination of the individual to

the race, and a similarly-immense fertility. Thus, as quoted by Dr.

Carpenter, Fries says--“in a single individual of _Reticularia maxima_,

I have counted (calculated?) 10,000,000 sporules.” It needs but to

note the clouds of particles, so minute as to look like smoke, which

ripe puffballs give off when they are burst, and then to remember

that each particle is a potential fungus, to be impressed with the

almost inconceivable powers of propagation which these plants possess.

The Lichens, too, furnish examples. Though they are nothing like so

prolific as the _Fungi_ (the difference yielding, as we shall hereafter

see, further support to the general argument), yet there is a great

production of germs, and a proportionate sacrifice of the parental

individuality. Considerable areas of the thallus develop into the

fruit-bodies characteristic of the various fungi which, combined with

algæ, form the different lichens (various members of the _Ascomycetes_

and the _Basidiomycetes_). From these are produced great numbers of

ascospores or basidiospores, as the case may be. Very many lichens also

reproduce themselves by means of _Soredia_, _i.e._, little masses of

algal cells closely wrapped in a weft of fungal hyphæ. Some contrasts

presented by the higher _Algæ_ may also be named as exemplifying the

inverse proportion between the size of the individual and the extent of

the generative structures. While in the smaller kinds relatively large

portions of the fronds are transformed into reproductive elements, in

the larger kinds these portions are relatively small: instance the

_Macrocystis pyrifera_, a gigantic seaweed which sometimes attains a

length of 1,500 feet, of which Dr. Carpenter remarks--“This development

of the nutritive surface takes place at the expense of the fructifying

apparatus, which is here quite subordinate.”

When we turn to vegetal aggregates of the third order of composition,

facts having the same meaning are conspicuous. On the average

these higher plants are far larger than plants of a lower degree of

composition; and on the average their rates of sexual reproduction are

far less. Similarly if, among Archegoniates and Phænogams, we compare

the smaller types with the larger, we find them proportionately more

prolific. This is not manifest if we simply calculate the number of

seeds ripened by an individual in a single season; but it becomes

manifest if we take into account the further factor which here

complicates the result--the age at which sexual genesis commences. The

smaller Phænogams are mostly either annuals, or perennials that die

down annually; and seeding as they do annually before their deaths, or

the deaths of their reproductive parts, it results that in the course

of a year each gives origin to a multitude of potential plants, of

which every one may the next year, if preserved, give origin to an

equal multitude. Supposing but a hundred offspring to be produced the

first year, ten thousand may be produced in the second year, a million

in the third, a hundred millions in the fourth. Meanwhile, what has

been the possible multiplication of a large Phænogam? While its small

congener has been seeding and dying, and leaving multitudinous progeny

to seed and die, it has simply been growing; and may so continue to

grow for ten or a dozen years without bearing fruit. Before a Cocoa-nut

tree has ripened its first cluster of nuts, the descendants of a wheat

plant, supposing them all to survive and multiply, will have become

numerous enough to occupy the whole surface of the Earth. So that

though, when it begins to bear, a tree may annually shed as many seeds

as an herb, yet in consequence of this delay in bearing, its fertility

is incomparably less; and its relatively-small fertility becomes still

further reduced where, as in _Lodoicea callipyge_, the seeds take two

years from the date of fertilization to the date of germination.

§ 340. Some observers state that in certain _Protozoa_ there occurs a

process of conjugation akin to that which the _Protophyta_ exhibit--a

coalescence of the substance of two individuals to form a germ-mass.

This has been alleged more especially of _Actinophrys_. If this

statement should be proved true,[58] then of the minute forms that

appear to be more animal than vegetal in their characters, some have

a mode of sexual multiplication by which the parents are sacrificed

bodily in the production of a new generation.

Among small animal aggregates of the second order, the first to be

considered are of course the _Cœlenterata_. A _Hydra_ occasionally

devotes a large part of its substance to sexual genesis. In the walls

of its body groups of ova, or spermatozoa, or both, take their rise;

and develop into masses greatly distorting the creature’s form, and

leaving it much diminished when they escape. Here, however, gamogenesis

is obviously supplementary to agamogenesis--the immensely rapid

multiplication by budding continues as long as food is abundant and

warmth sufficient, and is replaced by gamogenesis only at the close

of the season. A better example of the relation between small size

and active gamogenesis among low types of the _Metazoa_ is supplied

by the _Rotifera_. Microscopic as these are, they have a great rate

of sexual increase. According to Ehrenberg, _Hydatina senta_ “is

capable of a four-fold propagation every twenty-four or thirty hours,

bringing forth in this time four ova, which grow from the embryo to

maturity, and exclude their fertile ova in the same period. The same

individual, producing in ten days forty eggs, developed with the

rapidity above cited, this rate, raised to the tenth power, gives

one million of individuals from one parent, on the eleventh day

four millions, and on the twelfth day sixteen millions, and so on.”

Ehrenberg, however, characterized by Huxley as “the greatest looker

and the worst observer,” is not a safe authority, and it is better to

state the estimate of Ludwig Plate, who says that _Hydatina_ lays fifty

eggs in two to three weeks--a number which, multiplying in the manner

described, will yield in the time named a much smaller total though

still an enormous total.

The _Annulosa_, including among them the inferior types, have habits

and conditions of life so various that only the broadest contrasts can

be instanced in support of the proposition before us. The differences

of organization and activity greatly complicate the inverse variation

of fertility and bulk. Bearing in mind, however, that the rate of

multiplication depends much less on the number of each brood than on

the quickness with which maturity is reached and a new generation

commenced, it will be obvious that though Annelids, relatively

enormous in size, produce great numbers of ova, yet as they do this at

comparatively long intervals, their rates of increase fall immensely

below that just instanced in the Rotifers. And when at the other

extreme we come to the large articulate animals, such as the Crab

and the Lobster, the further diminution of fertility is seen in the

still longer delay which occurs before each new generation begins to

reproduce.

Perhaps the best examples are supplied by vertebrate animals, and

especially those that are most familiar to us. Comparisons between

Fishes are unsatisfactory, because of our ignorance of their histories.

In some cases Fishes equal in bulk produce widely different numbers of

eggs; as the Cod which spawns millions at once, and the Salmon by which

nothing like so great a number is spawned. But then the eggs are very

unlike in size; and if the ovaria of the two fishes be compared, the

difference between their masses is comparatively moderate. There are,

indeed, contrasts which seem at variance with the alleged relation; as

that between the Cod and the Stickleback which, though so much smaller,

produces fewer ova. The Stickleback’s ova, however, are relatively

large; and their total bulk bears as great a ratio to the bulk of the

Stickleback as does the bulk of the Cod’s ova to that of the Cod.

Moreover if, as is not improbable, the reproductive age is arrived

at earlier by the Stickleback than by the Cod, the fertility of the

species may be greater notwithstanding the smaller number produced

by each individual. Evidence which admits of being tolerably well

disentangled is furnished by Birds. They differ but little in their

grades of organization; and the habits of life throughout extensive

groups of them are so similar, that comparisons may be fairly made. It

is true that, as hereafter to be shown, the differences of expenditure

which differences of bulk entail, have doubtless much to do with the

differences of fertility. But we may set down under the present head

some of those cases in which the activity, being relatively slight,

does not greatly interfere with the relation we are considering; and

may note that among such birds having similarly slight activities, the

small produce more eggs than the large, and eggs that bear in their

total mass a greater ratio to the mass of the parent. Consider, for

example, the gallinaceous birds; which are like one another and unlike

birds of most other groups in flying comparatively little. Taking

first the wild members of this order, which rarely breed more than

once in a season, we find that the Pheasant has from 10 to 14 eggs,

the Black-cock from 6 to 10, the Grouse 8 to 14, the Partridge 12 to

20, the Quail still more, sometimes reaching two broods of 7 to 12 in

each. Here the only exception to the relation between decreasing bulk

and increasing number of eggs, occurs in the cases of the Pheasant

and the Black-cock; and it is to be remembered, in explanation, that

the Pheasant is constitutionally adapted to a warmer region, is

better fed--often artificially--and leads a less active life. If we

pass to domesticated genera of the same order, we meet with parallel

differences. From the numbers of eggs laid, little can be inferred;

for under the favourable conditions artificially maintained, the

laying is carried on indefinitely. But though in the sizes of their

broods the Turkey and the Fowl do not greatly differ, the Fowl begins

breeding at a much earlier age than the Turkey, and produces broods

more frequently: a considerably higher rate of multiplication being

the result. Now these contrasts among domestic creatures which are

similarly conditioned, and closely-allied by constitution, may be held

to show, more clearly than most other contrasts, the inverse variation

between bulk and sexual genesis; since here the cost of activity is

diminished to a comparatively small amount. There is little expenditure

in flight--sometimes almost none; and the expenditure in walking about

is not great: there is more of standing than of actual movement. It

is true that young Turkeys commence their existence as larger masses

than chickens; but it is tolerably manifest that the total weight of

the eggs laid by a Turkey during each season, bears a less ratio to

the Turkey’s weight, than the total weight of the eggs which a Hen

lays during each season, bears to the Hen’s weight; and this is the

fairest way of making the comparison. The comparison so made shows

a greater difference than appears likely to be due to the different

costs of locomotion; considering the inertness of the creatures.

Remembering that the assimilating surface increases only as the

squares of the dimensions, while the mass of the fabric to be built up

by the absorbed nutriment increases as the cubes of the dimensions,

it will be seen that the expense of growth becomes relatively greater

with each increment of size; and that hence, of two similar creatures

commencing life with different sizes, the larger one in reaching its

superior adult bulk, will do this at a more than proportionate expense;

and so will either be delayed in commencing its reproduction, or will

have a diminished reserve for reproduction, or both. Other orders

of Birds, active in their habits, show more markedly the connexion

between augmenting mass and declining fertility. But in them the

increasing cost of locomotion becomes an important, and probably the

most important, factor. The evidence they furnish will therefore

come better under another head. Contrasts among Mammals, like those

which Birds present, have their meanings obscured by inequalities of

the expenditures for motion. The smaller fertility which habitually

accompanies greater bulk, must in all cases be partly ascribed to this.

Still, it may be well if we briefly note, for as much as they are

worth, the broader contrasts. While a large Mammal bears but a single

young one at a time, is several years before it commences doing this,

and then repeats the reproduction at long intervals; we find, as we

descend to the smaller members of the class, a very early commencement

of breeding, an increasing number at a birth, reaching in small Rodents

to 10 or even more, and a much more frequent recurrence of broods: the

combined result being a relatively prodigious fertility. If a specific

comparison be desired between Mammals that are similar in constitution,

in food, in conditions of life, and all other things but size, the

Deer-tribe supplies it. While the large Red-deer has but one at a

birth, the small Roe-deer has frequently two at a birth.[59]

§ 341. The antagonism between growth and sexual genesis, visible in

these general contrasts, may also be traced in the history of each

plant and animal. So familiar is the fact that sexual genesis does not

occur early in life, and in all organisms which expend much begins only

when the limit of size is nearly reached, that we do not sufficiently

note its significance. It is a general physiological truth, however,

that while the building-up of the individual is going on rapidly, the

reproductive organs remain imperfectly developed and inactive; and that

the commencement of reproduction at once indicates a declining rate

of growth, and becomes a cause of arresting growth. As was shown in §

78, the exceptions to this rule are found where the limit of growth is

indefinite; either because the organism expends little or nothing in

action, or expends in action so moderate an amount that the supply of

nutriment is never equilibrated by its expenditure.

We will pass over the inferior plants and, limiting ourselves to

Phænogams, will not dwell on the less conspicuous evidence with the

smaller types present. A few cases such as gardens supply will serve.

All know that a Pear-tree increases in size for years before it begins

to bear; and that, producing but few pears at first, it is long before

it fruits abundantly. A young Mulberry-tree, branching out luxuriantly

season after season, but covered with nothing but leaves, at length

blossoms sparingly and sets some small and imperfect berries, which

it drops while they are green; and it makes these futile attempts

time after time before it succeeds in ripening any seeds. But these

multiaxial plants, or aggregates of individuals some of which continue

to grow while others become arrested and transformed into seed-bearers,

show us the relation less definitely than certain plants that are

substantially, if not literally, uniaxial. Of these the Cocoa-nut may

be instanced. For some years it goes on shooting up without making

any sign of becoming fertile. About the sixth year it flowers; but

the flowers wither without result. In the seventh year it flowers and

produces a few nuts; but these prove abortive and drop. In the eighth

year it ripens a moderate number of nuts; and afterwards increases

the number until, in the tenth year, it comes into full bearing.

Meanwhile, from the time of its first flowering its growth begins

to diminish, and goes on diminishing till the tenth year, when it

ceases. Here we see the antagonism between growth and sexual genesis

under both its aspects--see a struggle between self-evolution and

race-evolution, in which the first for a time overcomes the last, and

the last ultimately overcomes the first. The continued aggrandizement

of the parent-individual makes abortive for two seasons the tendency to

produce new individuals; and the tendency to produce new individuals,

becoming more decided, stops any further aggrandizement of the parent

individual.

Parallel illustrations occur in the animal kingdom. The eggs laid by a

pullet are relatively small and few. Similarly, it is alleged that, as

a general rule, “a bitch has fewer puppies at first, than afterwards.”

According to Burdach, as quoted by Dr. Duncan, “the elk, the bear, &c.,

have at first only a single young one, then they come to have most

frequently two, and at last again only one. The young hamster produces

only from three to six young ones, while that of a more advanced age

produces from eight to sixteen. The same is true of the pig.” It is

remarked by Buffon that when a sow of less than a year old has young,

the number of the litter is small, and its members are feeble and even

imperfect. Here we have evidence that in animals growth checks sexual

genesis. And then, on the other hand, we have evidence that sexual

genesis checks growth. It is well known to breeders that if a filly

is allowed to bear a foal, she is thereby prevented from reaching

her proper size. And a like loss of perfection as an individual,

is suffered by a cow which breeds too early. It may be added, as a

converse fact, that castrated animals, as capons and notably cats,

often become larger than their unmutilated associates.

§ 342. Notwithstanding the way in which the inverse variation of

growth and sexual genesis is complicated with other relations, its

existence is, I think, sufficiently manifest. Individually, many of

the foregoing instances are open to criticism, and have to be taken

with qualifications; but when looked at in the mass their meaning is

beyond doubt. Comparisons between the largest with the smallest types,

whether vegetal or animal, yield results which are unmistakable. On

the one hand, remembering the fact that during its centuries of life

an Oak does not produce as many acorns as a Fungus does spores in a

single night, we see that the Fungus has a fertility exceeding that

of the Oak in a degree literally beyond our powers of calculation or

imagination. On the other hand when, taking a microscopic protophyte

which has billions of descendants in a few days, we ask how many such

would be required to build up the forest tree which is years before

it drops a seed, we are met by a parallel difficulty in conceiving

the number, if not in setting it down. Similarly, if from the minute

and prodigiously-fertile Rotifer we turn to the Elephant, which

approaches thirty years before it bears a solitary young one, we find

the connexions between small size and great fertility and between great

size and small fertility, too intensely marked to be much disguised by

the perturbing relations that have been indicated. Finally, as this

induction, reached by a survey of organisms in general, is verified by

observations on the relation between decreasing growth and commencing

reproduction in individual organisms, we may, I think, consider the

alleged antagonism as proved.[60]

CHAPTER VII.

THE ANTAGONISM BETWEEN DEVELOPMENT AND GENESIS, ASEXUAL AND SEXUAL.

§ 343. By Development, as here to be dealt with apart from Growth, is

meant increase of structure as distinguished from increase of mass. As

was pointed out in § 50, this is the biological definition of the word.

In the following sections, then, we have to note how complexity of

organization is hindered by reproductive activity, and conversely.

This relation partially coincides with that which we have just

contemplated; for, as was shown in § 44, degree of growth is to a

considerable extent dependent on degree of organization. But while the

antagonism to be illustrated in this chapter is much entangled with

that illustrated in the last chapter, it may be so far separated as to

be identified as an additional antagonism.

Besides the direct opposition between that continual disintegration

which rapid genesis implies, and the fulfilment of that pre-requisite

to extensive organization--the formation of an extensive aggregate,

there is an indirect opposition which we may recognize under several

aspects. The change from homogeneity to heterogeneity takes time;

and time taken in transforming a relatively-structureless mass into

a developed individual, delays the period of reproduction. Usually

this time is merged in that taken for growth; but certain cases of

metamorphosis show us the one separate from the other. An insect,

passing from its lowly-organized caterpillar-stage into that of

chrysalis, is afterwards a week, a fortnight, or a longer period in

completing its structure: the re-commencement of genesis being by so

much postponed, and the rate of multiplication therefore diminished.

Further, that re-arrangement of substance which development implies,

entails expenditure. The chrysalis loses weight in the course of its

transformation; and that its loss is not loss of water only, may

be inferred from the fact that it respires, and that respiration

indicates consumption. Clearly the matter consumed is, other things

equal, a deduction from the surplus which may go to reproduction.

Yet again, the more widely and completely an organic mass becomes

differentiated, the smaller is the portion of it which retains the

relatively-undifferentiated state that admits of being moulded into

new individuals, or the germs of them. Protoplasm which has become

specialized tissue cannot be generalized afresh, and afterwards

transformed into something else; and hence the progress of structure

in an organism, by diminishing the unstructured part, diminishes the

amount available for making offspring.

It is true that higher structure, like greater growth, may insure to

a species advantages which eventually further its multiplication--may

give it access to larger supplies of food, or enable it to obtain food

more economically; and we shall hereafter see how the inverse variation

we are considering is thus qualified. But here we are concerned

only with the necessary and direct effects; not with those that are

contingent and remote. These necessary and direct effects we will now

look at as exemplified.

§ 344. Speaking generally, the simpler plants propagate both

sexually and asexually; and, speaking comparatively, the complex

plants propagate only sexually: their asexual propagation is usually

incomplete--produces a united aggregate of individuals instead of

numerous distinct individuals. The Protophytes that perpetually

subdivide, the merely cellular _Algæ_ that shed their tetraspores, the

Archegoniates that spontaneously separate their fronds or drop their

gemmæ, show us an extra mode of multiplication which, among flowering

plants, is exceptional. This extra mode of multiplication among these

simpler plants, is made easy by their low development. Tetraspores

arise only where the frond consists of untransformed cells; gemmæ bud

out and drop off only where the tissue is comparatively homogeneous.

Should it be said that this is but another aspect of the antagonism

already set forth, since these undeveloped forms are also the smaller

forms; the reply is that though in part true this is not wholly true.

Various marine _Algæ_ which propagate asexually, are larger than some

Phænogams which do not thus propagate. The objection that difference of

medium vitiates this comparison, is met by the fact that it is the same

among land-plants themselves. Sundry of the lowly-organized Liverworts

which are habitually gemmiparous, exceed in size many flowering plants.

And the Ferns show us agamic multiplication occurring in plants which,

while they are inferior in complexity of structure, are superior in

bulk to numbers of annual Monocotyledons and Dicotyledons.

§ 345. In the ability of the lowly-organized substance of a Sponge to

transform itself into multitudes of gemmules, we have an instance of

this same direct relation in the animal kingdom. Moreover, the instance

yields very distinct proof of an antagonism between development and

genesis, independent of the antagonism between growth and genesis; for

the Sponge which thus multiplies itself asexually, as well as sexually,

is far larger than hosts of more complex animals which do not multiply

asexually.

Once again may be cited the creature so often brought in evidence, the

_Hydra_, as showing us how rapidity of agamic propagation is associated

with inferiority of structure. Its power to produce young ones from

nearly all parts of its body, is due to the comparative homogeneity

of its body. In kindred but more-organized types, the gemmiparity is

greatly restricted, or disappears. Among the free-swimming _Hydrozoa_,

multiplication by budding, when it occurs at all, occurs only at

special places. That increase of structure apart from increase of size,

is here a cause of declining agamogenesis, we may see in the contrast

between the simple _Hydra_ and the compound Hydroids. These last, along

with more-differentiated tissues, show us a gemmation which does not

go on all over the body of each polype, and much of it does not end in

separation.

It is, however, among the _Annulosa_ that progressing organization

is most conspicuously operative in diminishing agamogenesis. The

segments or “somites” composing an animal belonging to this class, are

primordially alike; and, as before argued (§§ 205–7), are probably

the homologues of what were originally independent individuals. The

progress from the lower to the higher types of the class, is at once

a progress towards types in which the strings of segments cease to

undergo subdivision, and towards types in which the segments, no longer

alike in their structures and functions, have become physiologically

integrated or mutually dependent. Already this group of cases has

been named as illustrating the antagonism between growth and asexual

genesis; but it is proper also to name it here, since, on the one hand,

the greater size due to the ceasing of fission, is made possible only

by the specialization of parts and the development of a co-ordinating

apparatus to combine their actions, and since, on the other hand,

specialization and co-ordination can advance only in proportion as

fission ceases.

§ 346. The inverse variation of development and sexual genesis is by no

means easy to follow. One or two facts indicative of it may, however,

be named.

Phænogams that have but little supporting tissue may fairly be classed

as structurally inferior to those having stems with a bulky and

complex woody system; for these imply additional differentiations,

and constitute wider departures from the primitive type of vegetal

tissue. That the concomitant of this higher organization is a slower

gamogenesis, scarcely needs pointing out. While the herbaceous annual

is blossoming and ripening seed, the young tree is transforming its

originally-succulent axis into dense fibrous substance; and year

by year the young tree expends in doing the like, nutriment which

successive generations of the annual expend in fruit. Here the inverse

relation is between sexual reproduction and complexity, and not between

sexual reproduction and bulk, seeing that besides seeding, the annual

often grows to a size greater than that reached by the young infertile

tree in several years.

Proof of the antagonism between complexity and gamogenesis in animals,

is still more difficult to disentangle. Perhaps the evidence most to

the point is furnished by the contrast between Man and certain other

Mammals approaching him in mass. To compare him with the domestic Sheep

which, though not very unlike in size, is relatively prolific, is

objectionable because of the relative inactivity of Sheep; and this,

too, may be alleged as a reason why the Ox, though far more bulky, is

also far more fertile, than Man. Further, against a comparison with

the Horse which, while both larger and more prolific, is tolerably

active, it may be urged that in his case, and the cases of herbivorous

creatures generally, the small exertion required to procure food,

joined with the great ratio borne by the alimentary organs to the

organs they have to build up and repair, vitiates the result. We may,

however, fairly draw a parallel between Man and a large carnivore. The

Lion, superior in size, and perhaps equal in activity, has a digestive

system not proportionately greater; and yet has a higher rate of

multiplication than Man. Here the only decided want of parity, besides

that of organization, is that of food. Possibly a carnivore gains an

advantage in having a surplus nutriment consisting almost wholly of

those nitrogenous materials from which the bodies of young ones are

mainly formed. But, allowing for all other differences, it appears not

improbable that the smallness of human fertility compared with the

fertility of large feline animals, is due to the greater complexity of

the human organization--more especially the organization of the nervous

system. Taking degree of nervous organization as the chief correlative

of mental capacity; and remembering the physiological cost of that

slow evolution whereby high mental capacity is reached; we may suspect

that nervous organization is very expensive: the inference being that

bringing it up to the level it reaches in Man, whose digestive system,

by no means large, has at the same time to supply materials for general

growth and daily waste, involves a great retardation of maturity and

sexual genesis.

CHAPTER VIII.

ANTAGONISM BETWEEN EXPENDITURE AND GENESIS.

§ 347. Under this head we have to set down no evidence derived from the

vegetal kingdom. Plants are not expenders of force in such degrees as

to affect the general relations with which we are dealing. They have

not to maintain a heat above that of their environment, nor have they

to generate motion; and hence consumption for these two purposes does

not diminish the stock of material which serves on the one hand for

growth and on the other hand for propagation.

It will be well, too, if we pass over the lower animals: especially

those aquatic ones which, being nearly of the same temperature as

the water, and nearly of the same specific gravity, lose but little

in evolving motion, sensible and insensible. A further reason for

excluding from consideration these inferior types, is that we do not

know enough of their rates of genesis to permit of our making, with any

satisfaction, those involved comparisons here to be entered upon.

The facts on which we must mainly depend are those to be gathered

from terrestrial animals, and chiefly from those higher classes of

them which are at the same time great expenders and have rates of

multiplication about which our knowledge is tolerably definite. We

will restrict ourselves, then, to the evidence which Birds and Mammals

supply.

§ 348. Satisfactory proof that loss of substance in the maintenance of

heat diminishes the rapidity of propagation, is difficult to obtain.

It is, indeed, obvious that the warmblooded _Vertebrata_ are less

prolific than the cold-blooded; but then they are at the same time

more vivacious. Similarly, between Mammals and Birds (which are the

warmer-blooded of the two) there is, other things equal, a parallel,

though much smaller, difference; but here, too, the unlikenesses of

muscular action complicate the evidence. Again, the annual return of

generative activity has an average correspondence with the annual

return of a warmer season, which, did it stand alone, might be taken

as evidence that a diminished cost of heat-maintenance leads to such a

surplus as makes reproduction possible. But then, this periodic rise of

temperature is habitually accompanied by an increase in the quantity

of food--a factor of equal or greater importance. We must be content,

therefore, with such few special facts as admit of being disentangled.

Certain of these we are introduced to by the general relation last

named--the habitual recurrence of genesis with the recurrence of

spring. For in some cases a domesticated creature has its supplies

of food almost equalized; and hence the effect of varying nutrition

may be in great part eliminated from the comparison. The common

Fowl yields an illustration. It is fed through the cold months, but

nevertheless, in mid-winter, it either wholly leaves off laying or

lays very sparingly. And then we have the further evidence that if it

lays sparingly, it does so only on condition that the heat, as well as

the food, is artificially maintained. Hens lay in cold weather only

when they are kept warm. To which fact may be added the kindred one

that “when pigeons receive artificial heat, they not only continue to

hatch longer in autumn, but will recommence in spring sooner than they

would otherwise do.” An analogous piece of evidence is that, in winter,

inadequately sheltered Cows either cease to give milk or give it in

diminished quantity. For though giving milk is not the same thing as

bearing a young one, yet, as milk is part of the material from which

a young one is built up, it is part of the outlay for reproductive

purposes, and diminution of it is a loss of reproductive power. Indeed

the case aptly illustrates, under another aspect, the struggle between

self-preservation and race-preservation. Maintenance of the cow’s life

depends on maintenance of its heat; and maintenance of its heat may

entail such reduction in the supply of milk as to cause the death of

the calf.

Evidence derived from the habits of the same or allied genera in

different climates, may naturally be looked for; but it is difficult

to get, and it can scarcely be expected that the remaining conditions

of existence will be so far similar as to allow of a fair comparison

being made. The only illustrative facts I have met with which seem

noteworthy, are some named by Mr. Gould in his work on _The Birds

of Australia_. He says:--“I must not omit to mention, too, the

extraordinary fecundity which prevails in Australia, many of its

smaller birds breeding three or four times in a season; but laying

fewer eggs in the early spring when insect life is less developed, and

a greater number later in the season, when the supply of insect food

has become more abundant. I have also some reason to believe that the

young of many species breed during the first season, for among others,

I frequently found one section of the Honey-eaters (the _Melithrepti_)

sitting upon eggs while still clothed in the brown dress of immaturity;

and we know that such is the case with the introduced _Gallinaceæ_ (or

poultry) three or four generations of which have been often produced in

the course of a year.” Though here Mr. Gould refers only to variation

in the quantity of food as a cause of variation in the rate of

multiplication, may we not suspect that warmth is a part-cause of the

high rate which he describes as general?

§ 349. Of the inverse variation between activity and genesis, we get

clear proof. Let us begin with that which Birds furnish.

First we have the average contrast, already hinted, between the

fertility of Birds and the fertility of Mammals. Comparing the large

with the large and the small with the small, we see that creatures

which continually go through the muscular exertion of sustaining

themselves in the air and propelling themselves rapidly through it,

are less prolific than creatures of equal weights which go through the

smaller exertion of moving about over solid surfaces. Predatory Birds

have fewer young ones than predatory Mammals of approximately the same

sizes. If we compare Rooks with Rats, or Finches with Mice, we find

like differences. And these differences are greater than at first

appears. For whereas among Mammals a mother is able, unaided, to bear

and suckle and rear half-way to maturity, a brood that probably weighs

more in proportion than does the brood of a Bird; a Bird, or at least

a Bird that flies much, is unable to do this. Both parents have to

help; and this indicates that the margin for reproduction in each adult

individual is smaller.

Among Birds themselves occur contrasts which may be next considered.

In the Raptorial class, various species of which, differing in their

sizes, are similarly active in their habits, we see that the small

are more prolific than the large. The Golden Eagle has usually 2

eggs: sometimes 3, sometimes only 1. As we descend to the Kites and

Falcons, the number is 2 or 3, and 3 or 4. And when we come to the

Sparrow-Hawk, 3 to 5 is the specified number. Similarly among the

Owls: while the Great Eagle-Owl has 2 or 3 eggs, the comparatively

small Common Owl has 4 or 5. As before hinted, it is impossible to say

what proportions of these differences are due to unlikenesses of bulk

merely, and what proportions are due to unlikenesses in the costs of

locomotion. But we may fairly assume that the unlikenesses in the costs

of locomotion are here the more important factors. Weights varying as

the cubes of the dimensions, while the surfaces of digestive systems

vary as the squares, the expense of flight increases more rapidly than

does the ability to take in nutriment; and as motion through the

air requires more effort than motion on the ground, this geometrical

progression tells more rapidly on Birds than on Mammals. Be this as

it may, however, these contrasts support the argument; as do various

others which may be set down. The Finch-family, for example, have

broods averaging about 5 in number, and have commonly 2 broods in

the season; while in the Crow-family the number of the brood is on

the average less, and there is but one brood in the season. And then

on descending to such small birds as the Wrens and the Tits, we have

8, 10, 12 to 15 eggs, and sometimes two broods in the year. One of

the best illustrations is furnished by the Swallow-tribe, throughout

which there is little or no difference in mode of life or in food. The

Sand-Martin, much the least of them, has 4 to 6 eggs and two broods;

the Swallow, somewhat larger, has 4 or 5; and the Swift (similar in

habits though unrelated), larger still, has but 2. Here we see a lower

fertility associated in part with greater size, but associated still

more conspicuously with greater expenditure. For the difference of

fertility is more than proportionate to the difference of bulk, as

shown in other cases; and for this greater difference there is the

reason, that the Swift has to support not only the cost of propelling

its larger mass through the air, but also the cost of propelling it at

a higher velocity.

Omitting much evidence of like nature, let us note that disclosed by

comparisons of certain groups of birds with other groups. “Skulkers”

is the descriptive title applied to the Water-Rail, the Corn-Crake,

and their allies, which evade enemies by concealment--consequently

expending but little in locomotion. These birds have relatively large

broods--6 to 11, 8 to 12, &c. Not less instructive are the contrasts

between the Gallinaceous Birds and other Birds of like sizes but more

active habits. The Partridge and the Wood-Pigeon are about equal in

bulk and have much the same food. Yet while the one has from 12 to 20

young ones, the other has but 2 young ones twice a-year: its annual

reproduction is less than one-third. It may be said that the ability

of the Partridge to bring up so large a brood, is due to that habit of

its tribe which one of its names, “Scrapers,” describes; and to the

accompanying habit of the young, which begin to get their own living as

soon as they are hatched: so saving the parents’ labour. Conversely,

it may be said that the inability of Pigeons to rear more than 2 at a

time, is caused by the necessity of fetching everything they eat. But

the alleged relation holds nevertheless. On the one hand, a great part

of the food which the Partridge chicks pick up, is food which, in their

absence, the mother would have picked up. Though each chick costs her

far less than a young Pigeon costs its parents, yet the whole of her

chicks cost her a great deal in the shape of abstinence--an abstinence

she can bear because she has to fly but little. On the other hand,

the Pigeon’s habit of laying and hatching but two eggs, must not be

referred to any foreseen necessity of going through so much labour in

supporting the young, but to a constitutional tendency established by

such labour. This is proved by the curious fact that when domesticated,

and saved from such labour by artificial feeding, Pigeons, says

Macgillivray (quoting Aitkin), “are frequently seen sitting on eggs

long before the former brood is able to leave the nest, so that the

parent bird has at the same time young birds and eggs to take care of.”

§ 350. Made to illustrate the effect of activity on fertility, most

comparisons among Mammals are objectionable: other circumstances are

not equal. A few, however, escape this criticism.

One is that between the Hare and the Rabbit. These are closely-allied

species of the same genus, similar in their diet but unlike in their

expenditures for locomotion. The relatively-inert Rabbit has 6 young

ones in a litter, and four litters a-year; while the relatively-active

Hare has but 2 to 5 in a litter. This is not all. The Rabbit begins to

breed at six months old; but a year elapses before the Hare begins

to breed. These two factors compounded, result in a difference of

fertility far greater than can be ascribed to unlikeness of the two

creatures in size.

Perhaps the most striking piece of evidence which Mammals furnish,

is the extreme infertility of our common Bat. The _Cheiroptera_ and

the _Rodentia_ are not very dissimilar in their internal structures.

Diversity of constitution, therefore, cannot vitiate the comparison

between Bats and Mice, which are about the same in size. Though their

diets differ, the difference is in favour of the Bat: its food being

exclusively animal while that of the Mouse is mainly vegetal. What now

are their respective rates of genesis? The Mouse has several litters in

a year of 5 to 7 in each; while the Bat produces only one at a time.

Whether the Bat repeats its one more frequently than the Mouse repeats

its 7 is not stated; but it is quite certain that even if it does so

(an absurd supposition), the more frequent repetition cannot be such

as to raise its fertility to anything like that of the Mouse. And this

relatively-low rate of multiplication we may fairly ascribe to its

relatively-high rate of expenditure.

Here let us note, in passing, an interesting example of the

way in which a species which has no specially-great power of

self-preservation, while its power of multiplication is extremely

small, nevertheless avoids extinction because it has to meet an

unusually-small total of race-destroying forces. Leaving out parasites,

the only enemy of the Bat is the Owl; and the Owl is sparingly

distributed.

§ 351. These general evidences may be enforced by some special

evidences. We have few opportunities of observing how, within the

same species, variations of expenditure are related to variations of

fertility. But a fact or two showing the connexion may be named.

Doctor Duncan quotes a statement to the point respecting the breeding

of dogs. Already in §341 I have extracted a part of this statement,

to the effect that before her growth is complete, a bitch bears at a

birth fewer puppies than when she becomes full-grown. An accompanying

allegation is, that her declining vigour is shown by a decrease in the

number of puppies contained in a litter, “ending in one or two.” And

then it is further alleged that, “as regards the amount of work a dog

has to perform, so will the decline be rapid or gradual; and hence, if

a bitch is worked hard year after year, she will fail rapidly, and the

diminution of her puppies will be accordingly; but if worked moderately

and well kept, she will fail gradually, and the diminution will be less

rapid.”

In this place, more fitly than elsewhere, may be added a fact of like

implication, though of a different order. Of course whether excessive

expenditure be in the continual repairs of nervo-muscular tissues or in

replacing other tissues, the reactive effects, if not quite the same,

will be similar--there will be a decrease of the surplus available for

genesis. If, then, in any animals there from time to time occur unusual

outlays for self-maintenance, we may expect the periods of such outlays

to be periods of diminished or arrested reproduction. That they are so

the moulting of birds shows us. When hens begin to moult they cease to

lay. While they are expending so much in producing new clothing, they

have nothing to expend for producing eggs.

CHAPTER IX.

COINCIDENCE BETWEEN HIGH NUTRITION AND GENESIS.

§ 352. Under this head may be grouped various facts which, in another

way, tell the same tale as those contained in the last chapter. The

evidence there put together went to show that increased cost of

self-maintenance entailed decreased power of propagation. The evidence

to be set down here, will go to show that power of propagation is

augmented by making self-maintenance unusually easy. For into this may

be translated the effect of abundant food.

To put the proposition more specifically--we have seen that after

individual growth, development, and daily consumption, have

been provided for, the surplus nutriment measures the rate of

multiplication. This surplus may be raised in amount by such changes in

the environment as bring a larger supply of the materials or forces on

which both parental life and the lives of offspring depend. Be there,

or be there not, any expenditure, a higher nutrition will make possible

a greater propagation. We may expect this to hold both of agamogenesis

and of gamogenesis; and we shall find that it does so.

§ 353. On multiaxial plants, the primary effect of surplus nutriment

is a production of large and numerous leaf-shoots. How this asexual

multiplication results from excessive nutrition, is well shown when the

leading axis, or a chief branch, is broken off towards its extremity.

The axillary buds below the breakage quickly swell and burst into

lateral shoots, which often put forth secondary shoots: two generations

of agamic individuals arise where there probably would have been none

but for the local abundance of sap, no longer drawn off. In like manner

the abnormal agamogenesis which we have in proliferous flowers, is

habitually accompanied by a general luxuriance, implying an unusual

plethora.

No less conclusive is the evidence furnished by agamogenesis in

animals. Sir John Dalyell, speaking of _Hydra tuba_, and of the period

before strobilization commences, says--“It is singular how much

propagation is promoted by abundant sustenance.” This Polype goes on

budding out young polypes from its sides, with a rapidity proportionate

to the supply of materials. So, too, is it with the agamic reproduction

of the _Aphis_. As cited by Professor Huxley, Kyber “states that he

raised viviparous broods of both this species (_Aphis Dianthi_) and

_A. Rosæ_ for four consecutive years, without any intervention of

males or oviparous females, and that the energy of the power of agamic

reproduction was at the end of that period undiminished. The rapidity

of the agamic proliferation throughout the whole period was directly

proportional to the amount of warmth and food supplied.”

In these cases the relation is not appreciably complicated by

expenditure. The parent having reached its limit of growth, the

absorbed food goes to asexual multiplication: scarcely any being

deducted for the maintenance of parental life.

§ 354. The sexual multiplication of organisms under changed conditions,

undergoes variations conforming to a parallel law. Cultivated plants

and domesticated animals yield us proof of this.

Facts showing that in cultivated plants sexual genesis increases with

nutrition, are obscured by facts showing that a less rapid asexual

genesis, and an incipient sexual genesis, accompany the fall from a

high to a moderate nutrition. The confounding of these two relations

has led to mistaken inferences. When treating of Genesis inductively,

we reached the generalization that “the products of a fertilized germ

go on accumulating by simple growth, so long as the forces whence

growth results are greatly in excess of the antagonist forces; but

that when diminution of the one set of forces, or increase of the

other, causes a considerable decline in this excess, and an approach

towards equilibrium, fertilized germs are again produced.” (§ 78.)

It was pointed out that this holds of organisms which multiply by

heterogenesis, as well as those which multiply by homogenesis.

And plants were referred to as illustrating, both generally and

locally, the decline of agamic multiplication and commencement of

gamic multiplication, along with a lessening rate of nutrition.

Now the many cases which are given of fruitfulness caused in trees

by depletion, are really cases of this change from agamogenesis

to gamogenesis; and simply go to prove that what would naturally

arise when decreased peripheral growth had followed increased size,

may be brought about artificially by diminishing the supply of

materials for growth. Cramping its roots in a pot, or cutting them,

or ringing its branches, will make a tree bear very early: bringing

about a premature establishment of that relative innutrition which

would have spontaneously arisen in course of time. Such facts by

no means show that in plants sexual genesis increases as nutrition

diminishes. When it has once set in, sexual genesis is scanty or

imperfect unless nutrition is good. Though the starved plant may

blossom, yet many of its blossoms will fail; and such seeds as it

produces will be ill-furnished with those enveloping structures and

that store of albumen, &c., needed to give good chances of successful

germination--the number of surviving offspring will be diminished. Were

it otherwise, the manuring of fields which are to bear seed-crops,

would be not simply useless but injurious. Were it otherwise, dunging

the roots of a fruit-tree would in all cases be impolitic; instead

of being impolitic only where the growth of sexless axes is still

luxuriant. Were it otherwise, a tree which has borne a heavy crop

should, by the consequent depletion, be led to bear a still heavier

crop next year; whereas it is apt to be wholly or partially barren next

year--has to recover a state of tolerably-high nutrition before its

sexual genesis again becomes large.

But the best illustrations are yielded by animals--those animals at

least in which we have, besides an increased supply of nutriment, a

diminished expenditure. Two classes of comparisons, alike in their

implications, may be made--comparisons between tame and wild animals of

the same species or genus, and comparisons between tame animals of the

same species differently treated.

To begin with Birds, let us first contrast the farm-yard _Gallinaceæ_

with their kindred of the fields and woods. Notwithstanding their

greater size, which, other things equal, should be accompanied by

smaller fertility, the domesticated kinds have more numerous offspring

than the wild kinds. A Turkey has a dozen in a brood, while a Pheasant

has from 6 to 10. Twice or thrice in a season, a Hen rears as many

chickens as a Partridge rears once in a season. Anserine birds show us

parallel differences. The Tame Goose sits on 13 to 18 eggs and often

sits a second time; but the Wild Goose sits on 5, 6, or 7, and these

are noted as considerably smaller. It is the same with Ducks. The

domesticated variety lays and hatches twice as many eggs as the wild

variety. And the like holds of Pigeons. After remarking of the _Columba

livia_ that “in spring when they have plenty of corn to pick from

the newly-sown fields, they begin to get fat and pair; and again in

harvest, when the corn is cut down,” Macgillivray goes on to say that

“the same pair when tamed generally breed four times” in the year. That

between different poultry-yards inequalities of fertility are caused by

inequalities in the supplies of food, is a familiar truth. High feeding

shows its effects not only in the continuous laying, but also in the

sizes of the eggs. Among directions given for obtaining eggs from

pullets late in the year, it is especially insisted on that they shall

have a generous diet. Respecting Pigeons Macgillivray writes:--“that

their breeding depends much on their having plenty of food to fatten

them, seems, I think, evident from the circumstance that, when tamed,

which they easily are, they are observed to breed in every month of

the year. I do not mean that the same pair will breed every month; but

some in the flock, if well fed, will breed at any season.” There may

be added a fact of like meaning which partially-domesticated birds

yield. The Sparrow is one of the Finch tribe that has taken to the

neighbourhood of houses; and by its boldness secures food not available

to its congeners. The result is that it has several broods in a season,

while its field-haunting kindred have none of them more than two

broods, and some have only one.

Equally clear proof that abundant nutriment raises the rate of

multiplication, occurs among Mammals. Compare the litters of the Dog

with the litters of the Wolf and the Fox. Whereas those of the one

range in number from 6 to 14, those of the others contain respectively

5 or 6 or occasionally 7, and 4 or 5 or rarely 6. Again, the Wild Cat

has 4 or 5 kittens; but the tame Cat has 5 or 6 kittens 2 or 3 times

a-year. So, too, is it with the Weasel tribe. The Stoat has 5 young

ones once a-year. The Ferret has 2 litters yearly, each containing

from 6 to 9; and this notwithstanding that it is the larger of the

two. Perhaps the most striking contrast is that between the wild and

tame varieties of the Pig. While the one produces, according to its

age, from 4 to 8 or 10 young ones once a year, the other produces

sometimes as many as 17 in a litter; or, in other cases, will bring

up 5 litters of 10 each in two years--a rate of reproduction which is

unparalleled in animals of as large a size.[61] And let us not omit to

note that this excessive fertility occurs where there is the greatest

inactivity--where there is plenty to eat and nothing to do. There is no

less distinct evidence that among domesticated Mammals themselves, the

well-fed individuals are more prolific than the ill-fed individuals. On

the high and comparatively-infertile Cotswolds, it is unusual for ewes

to have twins; but they very commonly have twins in the adjacent rich

valley of the Severn. Similarly, among the barren hills of the west of

Scotland, two lambs will be borne by about one ewe in twenty; whereas

in England, something like one ewe in three will bear two lambs. Nay,

in rich pastures, twins are more frequent than single births; and it

occasionally happens that, after a genial autumn and consequent good

grazing, a flock of ewes will next spring yield double their number of

lambs--the triplets balancing the uniparæ. So direct is this relation,

that I have heard a farmer assert his ability to foretell, from the

high, medium, or low, condition of an ewe in the autumn, whether she

will next spring bear two, or one, or none.

§ 355. An objection must here be met. Many facts may be brought to

prove that fatness is not accompanied by fertility but by barrenness;

and the inference drawn is that high feeding is unfavourable to

genesis. The premiss may be admitted while the conclusion is denied.

There is a distinction between what may be called normal plethora,

and an abnormal plethora, liable to be confounded with it. The one

is a mark of constitutional wealth; but the other is a mark of

constitutional poverty. Normal plethora is a superfluity of materials

both for the building up of tissue and the evolution of force; and

this is the plethora which we have found to be associated with unusual

fecundity. Abnormal plethora which, as truly alleged, is accompanied by

infecundity, is a superfluity of force-evolving materials joined with

either a positive or a relative deficiency of tissue-forming materials:

the increased bulk indicating this state, being really the bulk of so

much inert or dead matter. Note, first, a few of the facts which show

us that obesity implies physiological impoverishment.

Neither in brutes nor men does it ordinarily occur either in youth or

in that early maturity during which the vigour is the greatest and the

digestion the best: it does not habitually accompany the highest power

of taking up nutritive materials. When fatness arises in the prime of

life, whether from peculiarity of food or other circumstance, it is

not the sign of an increased total vitality. On the contrary, if great

muscular action has to be gone through, the fat must be got rid of;

either, as in a man, by training, or as in a horse that has grown bulky

while out at grass, by putting him on such more nutritive diet as oats.

The frequency of senile fatness, both in domesticated creatures and in

ourselves, has a similar implication. Whether we consider the smaller

ability of those who display it to withstand large demands on their

powers, or whether we consider the comparatively-inferior digestion

common among them, we see that the increased size indicates, not an

abundance of materials which the organism requires, but an abundance of

materials which it does not require. Of like meaning is the fact that

women who have had several children, and animals after they have gone

on bearing young for some time, frequently become fat; and lose their

fecundity as they do this. In such cases the fatness is not to be taken

as the cause of the infecundity; but the constitutional exhaustion

which the previous production of offspring has left, shows itself at

once in the failing fecundity and the commencing fatness. There is yet

another kind of evidence. Obesity not uncommonly sets in after the

system has been subject to debilitating influences. Often a serious

illness is followed by a corpulence to which there was previously no

tendency. And the prolonged administration of mercury, constitutionally

injurious as it is, sometimes produces a like effect.

Closer inquiry verifies the conclusion to which these facts point.

The microscope shows that along with the increase of bulk common in

advanced life, there goes on what is called “fatty degeneration:”

oil-globules are deposited where there should be particles of flesh--or

rather, we may say, the hydrocarbonaceous molecules locally produced

by decomposition of the nitrogenous molecules, have not been replaced

by other nitrogenous molecules, as they should have been. This fatty

degeneration is, indeed, a kind of local death. For so regarding it

we have not simply the reason that an active substance has its place

occupied by an inert substance; but we have the further reason that the

flesh of dead bodies, under certain conditions, is transformed into a

fatty matter called adipocere.

The infertility that accompanies fatness in domestic animals has,

however, other causes than that declining constitutional vigour which

the fatness commonly indicates. Being artificially fed, these animals

cannot always obtain what their systems need. That which is given to

them is given expressly because of its fattening quality. And since the

capacity of the digestive apparatus remains the same, the absorption

of fat-producing materials in excess, implies defect in the absorption

of materials from which the tissues are formed, and out of which young

ones are built up. Moreover, this special feeding with a view to rapid

and early fattening, continued as it is through generations, and

accompanied as it is by a selection of individuals and varieties which

fatten most readily, tends to establish a modified constitution, more

fitted for producing fat and correspondingly-less fitted for producing

flesh--a constitution which, from this relatively-deficient absorption

of nitrogenous matters, is likely to become infertile; as, indeed,

these varieties often do become. Hence, no conclusions respecting the

effects of high nutrition, properly so-called, can be drawn from cases

of this kind. The cases are, in truth, of a kind which could not exist

but for human agency. Under natural conditions no animal would diet

itself in the way required to produce such results. And if it did its

race would quickly disappear.[62]

There is yet another mode in which accumulation of fat diminishes

fertility. Even supposing it unaccompanied by a smaller absorption of

nitrogenous materials, it is still a cause of lessening the surplus

of nitrogenous materials. For the repair of the motor tissues becomes

more costly. Fat stored-up is weight to be carried. A creature loaded

with inert matter must, other things equal, consume a greater amount

of tissue-forming substances for keeping its locomotive apparatus

in order; and thus expending more for self-maintenance can expend

less for race-maintenance. Abnormal plethora is thus antagonistic

to reproduction in a double way. It ordinarily implies a smaller

absorption of tissue-forming matters, and an increased demand on

the diminished supply. Hence fertility decreases in a geometrical

progression.

The counter-conclusion drawn from facts of this class is, then, due

to a misconception of their nature--a misconception arising partly

from the circumstance that the increase of bulk produced by fat is

somewhat like the increase of bulk which growth of tissues causes,

and partly from the circumstance that abundance of good food normally

produces a certain quantity of fat, which, within narrow limits, is

a valuable store of force-evolving material. When, however, we limit

the phrase high nutrition to its proper meaning--an abundance of, and

due proportion among, all the substances which the organism needs--we

find that, other things equal, fertility always increases as nutrition

increases. And we see that these apparently-exceptional cases, are

cases which really show us the same thing; since they are cases of

relative innutrition.

* * * * *

[NOTE.--By a strange oversight when writing this chapter

in the first edition--an oversight I was on the eve of repeating in

this present edition--I omitted to bring forward the familiar and

all-important evidence furnished by the variations of genesis which

ordinarily accompany the alternations of the seasons. These variations,

in multitudinous creatures of all types, show unmistakably that

reproduction begins at those times of the year when greater warmth

and larger supplies of food render maintenance of individual life

relatively easy, and when there is therefore a surplus available for

producing new individuals. Conversely, along with the decrease of

heat and the relative deficiency of food which make it comparatively

difficult in winter to maintain individual life, there ceases to be

the power of producing other lives: the reproductive organs become

quiescent and often dwindle. With this general fact is associated

a special fact. Though among wild animals--birds, mammals, and

others--breeding ceases when Nature no longer supplies abundant food

and warmth; in domesticated mammals and birds, artificially supplied

with food and warmth, the breeding season is greatly extended and often

made continuous, as, under the same conditions, it is in Man himself.

Evidence yielded by the vegetal world is less conspicuous, for the

reason that the cold which arrests reproductive activity also arrests

individual activity: growth of the individual and multiplication of

the race vary simultaneously with variations in the seasons. Still

there are some familiar facts showing that the external conditions

which favour nutrition also bring about reproduction. Early in the

year we are supplied with flowers from regions warmer than our own,

and by and by there come to our markets fruits and vegetables from the

south of France, the Channel Islands, and even from the Scilly Isles,

which are much in advance of those furnished by the gardens of our own

colder regions: reproduction commences earlier where the light and

heat furthering nutrition are greater. And then there is a kindred

meaning in the not unfrequent occurrence of a second flowering and even

of a second fruiting in warm, bright and prolonged autumns. Here the

abnormal re-commencement of reproduction is determined by an abnormal

increase of nutrition.]

CHAPTER X.

SPECIALITIES OF THESE RELATIONS.

§ 356. Tests of the general doctrines set forth in preceding chapters,

are afforded by organisms having modes of life which diverge widely

from ordinary modes. Here, as elsewhere, aberrant cases yield crucial

proofs.

If certain organisms are so circumstanced that highly-nutritive matter

is supplied to them without stint, and they have nothing to do but

absorb it, we may infer that their powers of propagation will be

enormous.

If there are classes of creatures which expend very little for

self-support in comparison with allied creatures, a relatively-extreme

prolificness may be expected of them.

Or if, again, we find species presenting the peculiarity that while

some of their individuals have much to do and little to eat, others of

their individuals have much to eat and little to do, we may look for

great fertility in these last and comparative infertility or barrenness

in the first.

These several anticipations we shall find completely verified.

§ 357. Plants which, like the _Rafflesiaceæ_, carry their parasitism

to the extent of living on the juices they absorb from other plants,

exhibit one of these relations in the vegetal kingdom. In them the

organs for self-support being needless, are rudimentary; and the parts

directly or indirectly concerned in the production and distribution of

germs, constitute the mass of the organism. That small ratio which the

race-preserving structures bear to the self-preserving structures in

ordinary Phænogams, is, in these Phænogams, inverted. A like relation

occurs in the common Dodder.

There may be added a kindred piece of evidence which the _Fungi_

present. Those of them which grow on living plants, repeat the above

connection completely; and those of them which, though not parasitic,

nevertheless subsist on organized materials previously elaborated by

other plants, substantially repeat it. The spore-producing part is

relatively enormous; and the fertility is far greater than that of

Cryptogams of like sizes, which have to form for themselves the organic

compounds of which they and their germs consist.

§ 358. The same lesson is taught us by animal-parasites. Along with the

decreased cost of Individuation, they similarly show us an increased

expenditure for Genesis; and they show us this in the most striking

manner where the deviation from ordinary conditions of life is the

greatest.

Take, among the _Epizoa_, such an instance as _Chondracanthus

gibbosus_. Belonging to the _Entomostraca_, both males and females

of this species are, in their early days, similar to their allies;

and the males, practically parasitic, though they become greatly

degraded, continue throughout life to show by their segmentation and

other external traits their original nature. The female, however,

having fixed herself where she can suck the juices of her host, the

_Lophius_, grows to twelve times the length of the male and probably

a thousand times its bulk, and becomes utterly transformed by loss of

the organs of animal life and enormous development of the organs of

reproduction. “No heart is discoverable, and the nervous system and

organs of sense (if any) are equally undistinguishable. The interspace

between the alimentary canal and the walls of the body is almost wholly

occupied by the ovarium.”[63] And then beyond this there are appended

ovi-sacs twice the length of the body. So that the germ-producing

organs and their contents, eventually acquire a total bulk many times

that of all the other organs put together. Numerous species of this

type and habit, repeat this relation between a life of inaction with

high feeding, and an enormous rate of genesis. Parasites belonging to

another great division of the animal kingdom, the _Platyhelminthes_,

supply an example of an _epizoon_ in which the rate of multiplication

is made great not so much by immense development of the egg-producing

organs as by the rapidity with which generations succeed one another--a

rapidity such that each generation partially develops the next before

it is itself anything like ready for independent life. This is the

_Gyrodactylus elegans_, of which it is said that “its most remarkable

feature is that it is viviparous, and its embryos before they leave the

body of their mother have already developed their embryos inside them;

and the latter may contain their embryos, so that four generations may

be included under the cuticle of the sexually mature animal.”[64]

_Entozoa_ yield us many examples of this causal relation, raised to

a still higher degree. The _Gordius_, or Hair-worm, is a creature

which, finding its way when young into the body of an insect which is

afterwards swallowed by a fish, there grows rapidly, and then emerging

to breed, lays as many as 8,000,000 eggs in less than a day. Similarly

with those larger types infesting the higher animals. It has been

calculated by Dr. Eschricht, as quoted by Professor Owen, that there

are “64,000,000 of ova in the mature female _Ascaris lumbricoides_.”

Very many of the _Entozoa_ belong to the _Platyhelminthes_, and among

them occur examples of fertility caused not only by great numbers of

ova, but by rapid succession of partially-developed individuals and

also examples of fertility caused by production of ova almost exceeding

numeration. Among the first the Liver-fluke may be named. Of the

half-million eggs it produces each yields a free-swimming ciliated

embryo, and any one of these, which finds its way into a water-snail,

becomes a sporocyst--a bag, presently occupied exclusively by masses

of cells: each mass by and by becoming a _Redia_, which makes its way

out. Like all its fellows which develop in succession, this, with

the exception of a small space occupied by the stomach, devotes the

whole of its interior partly to the formation of other _Rediæ_ (which

presently escape and become similarly transformed), and partly to the

development of _Cercariæ_, into which the internal substance of all

the _Rediæ_ is eventually transformed: _Cercariæ_ which, escaping

from the host, become agents for infecting other creatures. So that

each ovum thus gives rise to a number of forms which severally

subserve multiplication in different ways. Of the other division of

_Platyhelminthes_ referred to as carrying on its multiplication by

production of ova only, the commonest of the _Cestoidea_ furnishes the

best example. Immersed as a Tape-worm is in nutritive liquid, which it

absorbs through its integument, it requires no digestive apparatus. The

room which one would occupy, and the materials it would use up, are

therefore available for germ-producing organs, which nearly fill each

segment: each segment, sexually complete in itself, is little else than

an enormous reproductive system, with just enough of other structures

to bind it together. Remembering that the Tape-worm, retaining its

hold, continues to bud out such segments as fast as the fully-developed

ones are cast off, and goes on doing this as long as the infested

individual lives; we see that here, where there is no expenditure,

where the cost of individuation is reduced to the greatest extent while

the nutrition is the highest possible, the degree of fertility reaches

its extreme. These _Entozoa_ yield us further interesting evidence. Of

their various species, most if not all undergo passive migration from

animal to animal before they become mature. Usually, the form assumed

in the body of the first host is devoid of all that part in which the

reproductive structures take their rise; and this part grows and

develops reproductive structures, only in some predatory animal to

which its first host falls a sacrifice. Occasionally, however, the egg

gives origin to the sexual form in the animal that originally swallowed

it, but the development remains incomplete--there is no sexual genesis,

no formation of eggs in the rudimentary segments. That these may

become fertile it is needful, as before, for the containing animal to

be devoured; so that the imperfect Tape-worm may find its way into

the intestine of a higher animal. Thus the _Bothriocephalus solidus_,

found in the abdominal cavity of the Stickleback, is barren while it

remains there; but if the Stickleback be eaten by a Water-fowl, the

reproductive system of the transferred _Bothriocephalus_ (then known

as _B. nodosus_) becomes developed and active. So, too, a kind of

Tape-worm which remains infertile while in the intestine of a Mouse,

becomes fertile in the intestine of a Cat that devours the mouse. May

we not regard these facts as again showing the dependence of fertility

on nutrition? Barrenness here accompanies conditions unfavourable

to the absorption of nutriment; and it gives way to fecundity where

nutriment is large in quantity and superior in quality.

§ 359. Extremely significant are those cases of partial reversion to

primitive forms of genesis, which occur under special conditions in

some of the higher _Annulosa_. I refer to the pseudo-parthenogenesis

and metagenesis in Insects.

Under what conditions do the _Aphides_ exhibit this strange deviation

from the habits of their order? Why among them should imperfect

females produce, agamically, others like themselves, generation after

generation, with great rapidity? There is the obvious explanation that

they get plenty of easily-assimilated food without exertion. Piercing

the tender coats of young shoots, they sit and suck--appropriating

the nitrogenous elements of the sap and ejecting its saccharine

matter as “honey dew.” Along with a sluggishness strongly contrasted

with the activity of most insects--along with a very low rate of

consumption and a correlative degradation of structure; we have here

a retrogression to asexual genesis, and a greatly-increased rate of

multiplication.

The recently discovered instance of internal metagenesis in the

maggots of certain Flies has a like meaning. Incredible as it at first

seemed to naturalists, it is now proved that the _Cecydomia_-larva

develops in its interior a brood of larvæ of like structure with

itself. In this case, as in the last, abundant food is combined

with low expenditure. These larvæ are found in such habitats as the

refuse of beet-root-sugar factories--masses of nitrogenous _débris_

remaining after the extraction of the saccharine matter. Each larva

has a practically-unlimited supply of sustenance imbedding it on all

sides.[65]

It is true that some other maggots, as those of the Flesh-fly,

are similarly, or still better, circumstanced; and, it may be

said, ought therefore to have the same habit. But this does not

necessarily follow. Survival of the fittest will determine whether

such specially-favourable conditions result in aggrandizement of the

individual or in multiplication of the race. And in the case of the

Flesh-fly there is a reason why greater individuation rather than

more rapid genesis will occur. For a decomposing animal body lasts

so short a time, that were Flesh-fly larvae to multiply agamically,

the second generation would die from the disappearance of their food.

Hence individuals in which the excessive nutrition led to internal

metagenesis, would leave no posterity, and natural selection would

establish the variety in which greater growth resulted. All which the

argument requires is that when such reversion to agamogenesis _does_

take place, it shall be where the food is unusually abundant and the

expenditure unusually small; and this the cases instanced go to show.

§ 360. The physiological lesson taught us by Bees and Ants, not quite

harmonizing with the moral lesson they are supposed to teach, is that

highly-fed idleness is favourable to fertility, and that excessive

industry has barrenness for its concomitant.

The egg of a Bee develops into a small barren female or into a large

fertile female, according to the supply of food given to the larva

hatched from it. We here see that the germ-producing action is an

overflow of the surplus remaining after completion of the individual;

and that the lower feeding which the larva of a working Bee has,

results in a dwarfing of the adult and an arrested development of

the generative organs. Further, we have the fact that the condition

under which the perfect female, or mother-Bee, goes on, unlike insects

in general, laying eggs continuously, is that she has plenty of

food brought to her, is kept warm, and goes through no considerable

exertion. While, contrariwise, it is to be noted that the infertility

of the workers is associated with the ceaseless labour of bringing

materials for the combs and building them, as well as the labour of

feeding the queen, the larvæ, and themselves.

Ants also show us these relations, and they are shown in a greatly

exaggerated form by what are called white ants--insects belonging to

a quite different order. The contrast in bulk between the fecund and

infecund females is here immensely greater. The mother-Ant has the

reproductive system so enormously developed, that the remainder of her

body is relatively insignificant. Entirely incapable of locomotion,

she is unable to deposit her eggs in the places where they are to

be hatched; so that they have to be carried away by the workers as

fast as they are extruded. Her life is thus reduced substantially to

that of a parasite--an absorption of abundant food supplied gratis,

a total absence of expenditure, and a consequent excessive rate of

genesis. “The queen-ant of the African _Termites_ lays 80,000 eggs in

twenty-four hours.”

§ 361. It may be needful to say that these exceptional relations cannot

be ascribed to the assigned causes acting alone. The extreme fertility

which, among parasites and social insects, accompanies extremely high

feeding and an expenditure reduced nearly to zero, presupposes typical

structures and tendencies of suitable kinds; and these are not directly

accounted for. On creatures otherwise organized, unlimited supplies

of food and total inactivity are not followed by such results. There

of course requires a constitution fitted to the special conditions,

and the evolution of this cannot be due simply to plethora joined with

rest. These cases are given as illustrating the conditions under which

extreme exaltations of fertility become possible. Their meanings, thus

limited, are clear, and completely to the point. We see in them that

the devotion of nutriment to race-preservation, is carried furthest

where the cost of self-preservation is reduced to a minimum; and,

conversely, that nothing is devoted directly to race-preservation

by individuals on which falls an excessive expenditure for

self-preservation and preservation of other’s offspring.

* * * * *

[NOTE.--Among specialities of these relations may be fitly added here

a very strange one, for a description of which I am indebted to M.

Charles Julin, Professor of Comparative Anatomy in the University of

Liège. In the _Revue Générale des Sciences_ for 30th August, 1894, in

an account of certain investigations of M. Giard, he describes what

he calls “la castration parasitaire”--a castration not of a literal

kind but one effected by the arrest of development which follows from

the depletion caused by a parasite. The _Sacculina_ is an amazingly

transformed type belonging to the _Cirrhipedia_--a type without

segments or appendages and without mouth and alimentary canal. Fixing

itself, during its early locomotive stage, under the abdomen of a

decapodous crustacean, and leaving behind its exo-skeleton, it makes

its way into the interior, and there becoming a mere bag containing

the reproductive organs, obtains the needful nutriment by developing

what are practically roots and rootlets which run everywhere among the

viscera and absorb nutriment from the surrounding tissues. Here we

are concerned merely with the effect produced upon the host by this

physiological robbery. This effect is to arrest the development not

only of the primary sexual organs devoted to the production of germs,

but also of those secondary sexual organs which characterize the male.

M. Julin writes:--

“Il convient cependant de dire, pour être plus exact, que,

dans les cas des Crabes infesté par des Sacculines, il n’y a

pas, en réalité, apparition de caractères femelles chez le

sexe mâle, mais plutôt absence de développement des caractères

mâles. En fait, l’animal reste à un stade jeune, non différencié

sexuellement, tout en prenant une taille plus considérable. Cela

nous porte à attribuer les modifications dont nous avons parlé à

un simple arrêt de développement, qui est plus sensible chez le

mâle, parce que chez lui les caractères sexuels secondaires sont

à l’état normal plus développés que chez la femelle.

D’une manière générale, nous croyons, avec M. Giard, qu’il faut

assimiler les modifications dues à la castration parasitaire à

celles qui sont le résultat de la progenèse ou qui engendrent le

dimorphisme saisonnier.

Il y a _progenèse_ lorsque, chez un animal, la reproduction

sexuée s’opère d’une façon plus ou moins précoce, c’est-à-dire

lorsque les produits sexuels (œufs ou spermatozoïdes) se

forment et mûrissent avant que l’être n’ait atteint son complet

développement. On peut citer comme exemples les Axolotls et

les larves de Tritons qui, les uns normalement, les autres

accidentellement, pondent en ayant encore leurs branchies.

Très souvent la progenèse n’affecte qu’un seul sexe. Tantôt,

c’est le sexe femelle qui mûrit à l’état larvaire comme chez

les pucerons, les _Stylops_, etc.... Tantôt c’est le sexe mâle,

comme chez la Bonellie, les mâles complémentaires de Cirripèdes,

les mâles pygmées des Rotifères, le mâle de l’Anguille, etc.

D’autres fois, enfin, l’animal présente successivement les deux

sexes avec progenèse pour l’un d’entre eux. C’est ainsi qu’il

y a _progenèse protandrique_ chez les Crustacés cymothoadiens,

et, parmi les Vertébrés, chez les Myxines, qui, mâles dans le

jeune âge, deviennent femelles en vieillissant et en achevant

de prendre leur développement. Le cas des vieilles femelles de

Gallinacés à plumage et à instincts masculins semble être, au

contraire, un exemple imparfait de _progenèse protogynique_,

puisque ces femelles ont pondu lorsqu’elles avaient encore

la livrée des jeunes et qu’elles ont continué plus tard leur

développement, et présentent le caractère des mâles sans que,

cependant, l’on ait constaté la production de spermatozoïdes.

Dans les cas extrêmes de progenèse femelle, la reproduction se

fait même sans le concours de l’élément mâle, revenant ainsi

à la forme agamique primordiale. Ces cas sont connus depuis

longtemps sous le nom de _pédogenèse_. On les a observé chez les

larves de _Miastor_, de _Chironomus_ et chez certains pucerons.

Chaque fois qu’il y a progenèse dans un type déterminé, on

constate soit momentanément, soit d’une façon définitive, un

arrêt de croissance et de développement: l’animal progénétique

a, par suite, l’aspect d’une larve sexuée, lorsqu’on le compare

soit à l’autre sexe, soit aux formes voisines, qui ne présentent

pas le phénomène de la progenèse.

Cela est en parfaite harmonie avec le principe, si bien mis en

lumière par Herbert Spencer, de _l’antagonisme entre la genèse

et la croissance et entre la genèse et le développement_.

Cet antagonisme s’explique facilement si l’on songe que les

matériaux employés pour la reproduction ne peuvent servir à

l’accroissement de l’individu. S’il est avantageux pour un

organisme de se reproduire sans acquérir des organes inutiles,

la sélection naturelle déterminera bientôt une progenèse de plus

en plus complète. Les animaux parasites, outre qu’ils tirent de

leur hôte une nourriture abondante, n’ont guère besoin d’une

foule d’organes qui servent à leurs congénères libres dans la

vie de relation. Aussi voyons-nous qu’un très grand nombre

d’animaux parasites sont progénétiques. Les mâles progénétiques

de la Bonellie et des Cirripèdes vivent en parasites dans leurs

femelles. Chez certains types, les pucerons, la progenèse cesse

dès que, la nourriture devenant moins abondante, un déplacement

pourra être nécessaire.

En résumé, l’arrêt de développement dû à la progenèse résulte

d’une dérivation des principes nourriciers au détriment

de l’animal progénétique. Dans les exemples de castration

parasitaire que nous avons examinés, le parasite joue, par

rapport à son hôte, absolument le même rôle que la glande

génitale d’un type progénétique. Il détourne, pour sa propre

subsistance, une partie des principes qui auraient servi au

développement de l’animal. Aussi les effets produits sont-ils

tout à fait de même ordre.”

A phenomenon so anomalous as this, explicable upon the hypothesis set

forth but not otherwise explicable, furnishes striking verification.]

CHAPTER XI.

INTERPRETATION AND QUALIFICATION.