influence of a previous sire on progeny--which calls for comment. He sets
down what he supposes Weismann will say in response to my argument. "First,
he may question the fact." Well, after the additional evidence given above,
I think he is not likely to do that; unless, indeed, it be that along with
readiness to base conclusions on things "it is easy to imagine" there goes
reluctance to accept testimony which it is difficult to doubt. Second, he
is supposed to reply that "the Germ-plasm of the first sire has in some way
or another become partly commingled with that of the immature ova"; and Dr.
Romanes goes on to describe how there may be millions of spermatozoa and
"thousands of millions" of their contained "ids" around the ovaries, to
which these secondary effects are due. But, on the one hand, he does not
explain why in such cases each subsequent ovum, as it becomes matured, is
not fertilized by the sperm-cells present, or their contained germ-plasm,
rendering all subsequent fecundations needless; and, on the other hand, he
does not explain why, if this does not happen, the potency of this
remaining germ-plasm is nevertheless such as to affect not only the next
succeeding offspring, but all subsequent offspring. The irreconcilability
of these two implications would, I think, sufficiently dispose of the
supposition, even had we not daily multitudinous proofs that the surface of
a mammalian ovarium is not a spermatheca. The third reply Dr. Romanes
urges, is the inconceivability of the process by which the germ-plasm of a
preceding male parent affects the constitution of the female and her
subsequent offspring. In response, I have to ask why he piles up a mountain
of difficulties based on the assumption that Mr. Darwin's explanation of
heredity by "Pangenesis" is the only available explanation preceding that
of Weismann? and why he presents these difficulties to me, more especially;
deliberately ignoring my own hypothesis of physiological units? It cannot
be that he is ignorant of this hypothesis, since the work in which it is
variously set forth (_Principles of Biology_, §§ 66-97) is one with which
he is well acquainted: witness his _Scientific Evidences of Organic
Evolution_; and he has had recent reminders of it in Weismann's
_Germ-plasm_, where it is repeatedly referred to. Why, then, does he assume
that I abandon my own hypothesis and adopt that of Darwin; thereby
entangling myself in difficulties which my own hypothesis avoids? If, as I
have argued, the germ-plasm consists of substantially similar units (having
only those minute differences expressive of individual and ancestral
differences of structure), none of the complicated requirements which Dr.
Romanes emphasizes exist; and the alleged inconceivability disappears.
Here I must end: not intending to say more, unless for some very urgent
reason; and leaving others to carry on the discussion. I have, indeed, been
led to suspend for a short time my proper work, only by consciousness of
the transcendent importance of the question at issue. As I have before
contended, a right answer to the question whether acquired characters are
or are not inherited, underlies right beliefs, not only in Biology and
Psychology, but also in Education, Ethics, and Politics.
III.
As a species of literature, controversy is characterised by a terrible
fertility. Each proposition becomes the parent of half a dozen; so that a
few replies and rejoinders produce an unmanageable population of issues,
old and new, which end in being a nuisance to everybody. Remembering this,
I shall refrain from dealing with all the points of Professor Weismann's
answer. I must limit myself to a part; and that there may be no suspicion
of a selection convenient to myself, I will take those contained in his
first article.
Before dealing with his special arguments, let me say something about the
general mode of argument which Professor Weismann adopts.
The title of his article is "The All-Sufficiency of Natural
Selection."[117] Very soon, however, as on p. 322, we come to the
admission, which he has himself italicised, "that _it is really very
difficult to imagine this process of natural selection in its details_; and
to this day it is impossible to demonstrate it in any one point."
Elsewhere, as on pp. 327 and 336 _à propos_ of other cases, there are like
admissions. But now if the sufficiency of an assigned cause cannot in any
case be demonstrated, and if it is "really very difficult to imagine" in
what way it has produced its alleged effects, what becomes of the
"all-sufficiency" of the cause? How can its all-sufficiency be alleged when
its action can neither be demonstrated nor easily imagined? Evidently to
fit Professor Weismann's argument the title of the article should have been
"The Doubtful Sufficiency of Natural Selection."
Observe, again, how entirely opposite are the ways in which he treats his
own interpretation and the antagonist interpretation. He takes the problem
presented by certain beautifully adapted structures on the anterior legs of
"very many insects," which they use for cleansing their antennæ. These, he
argues, cannot have resulted from the inheritance of acquired characters;
since any supposed changes produced by function would be changes in the
chitinous exo-skeleton, which, being a dead substance, cannot have had its
changes transmitted. He then proceeds, very candidly, to point out the
extreme difficulties which lie in the way of supposing these structures to
have resulted from natural selection: admitting that an opponent might "say
that it was absurd" to assume that the successive small variations implied
were severally life-saving in their effects. Nevertheless, he holds it
unquestionable that natural selection has been the cause. See then the
difference. The supposition that the apparatus has been produced by the
inheritance of acquired characters is rejected _because_ it presents
insuperable difficulties. But the supposition that the apparatus has been
produced by natural selection is accepted, _though_ it presents insuperable
difficulties. If this mode of reasoning is allowable, no fair comparison
between diverse hypotheses can be made.
With these remarks on Professor Weismann's method at large, let me now pass
to the particular arguments he uses, taking them _seriatim_.
* * * * *
The first case he deals with is that of the progressive degradation of the
human little toe. This he considers a good test case; and he proceeds to
discuss an assigned cause--the inherited and accumulated effects of
boot-pressure. Without much difficulty he shows that this interpretation is
inadequate; since fusion of the phalanges, which constitutes in part the
progressive degradation, is found among peoples who go barefoot, and has
been found also in Egyptian mummies. Having thus disposed of Mr. Buckman's
interpretation, Professor Weismann forthwith concludes that the ascription
of this anatomical change to the inheritance of acquired characters is
disposed of, and assumes, as the only other possible interpretation, a
dwindling "through panmixia": "the hereditary degeneration of the little
toe is thus quite simply explained from my standpoint."
It is surprising that Professor Weismann should not have seen that there is
an explanation against which his criticism does not tell. If we go back to
the genesis of the human type from some lower type of _primates_, we see
that while the little toe has ceased to be of any use for climbing
purposes, it has not come into any considerable use for walking and
running. A glance at the feet of the sub-human _primates_ in general, shows
that the inner digits are, as compared with those of men, quite small, have
no such relative length and massiveness as the human great toes. Leaving
out the question of cause, it is manifest that the great toes have been
immensely developed, since there took place the change from arboreal habits
to terrestrial habits. A study of the mechanics of walking shows why this
has happened. Stability requires that the "line of direction" (the vertical
line let fall from the centre of gravity) shall fall within the base, and,
in walking, shall be brought at each step within the area of support, or so
near it that any tendency to fall may be checked at the next step. A
necessary result is that if, at each step, the chief stress of support is
thrown on the outer side of the foot, the body must be swayed so that the
"line of direction" may fall within the outer side of the foot, or close to
it; and when the next step is taken it must be similarly swayed in an
opposite way, so that the outer side of the other foot may bear the weight.
That is to say, the body must oscillate from side to side, or waddle. The
movements of a duck when walking or running show what happens when the
points of support are wide apart. Clearly this kind of movement conflicts
with efficient locomotion. There is a waste of muscular energy in making
these lateral movements, and they are at variance with the forward
movement. We may infer, then, that the developing man profited by throwing
the stress as much as possible on the inner sides of the feet; and was
especially led to do this when going fast, which enabled him to abridge the
oscillations: as indeed we now see in a drunken man. Thus there was thrown
a continually increasing stress upon the inner digits as they progressively
developed from the effects of use; until now that the inner digits, so
large compared with the others, bear the greater part of the weight, and
being relatively near one another, render needless any marked swayings from
side to side. But what has meanwhile happened to the outer digits?
Evidently as fast as the great toes have come more and more into play and
developed, the little toes have gone more and more out of play and have
been dwindling for--how long shall we say?--perhaps a hundred thousand
years.
So far, then, am I from feeling that Professor Weismann has here raised a
difficulty in the way of the doctrine I hold, that I feel indebted to him
for having drawn attention to a very strong evidence in its support. This
modification in the form of the foot, which has occurred since arboreal
habits have given place to terrestrial habits, shows the effects of use and
disuse simultaneously. The inner digits have increased by use while the
outer digits have decreased by disuse.
* * * * *
Saying that he will not "pause to refute other apparent proofs of the
transmission of acquired characters," Professor Weismann proceeds to deal
with the argument which, with various illustrations, I have several times
urged--the argument that the natural selection of fortuitously-arising
variations cannot account for the adjustment of co-operative parts. Very
clearly and very fairly he summarises this argument as used in _The
Principles of Biology_ in 1864. Admitting that in this case there are
"enormous difficulties" in the way of any other interpretation than the
inheritance of acquired characters, Professor Weismann before proceeding to
assault this "last bulwark of the Lamarckian principle," premises that the
inheritance of acquired characters cannot be a cause of change because
inactive as well as active parts degenerate when they cease to be of use:
instancing the "skin and skin-armature of crabs and insects." On this I may
remark in the first place that an argument derived from degeneracy of
passive structures scarcely meets the case of development of active
structures; and I may remark in the second place that I have never dreamt
of denying the efficiency of natural selection as a cause of degeneracy in
passive structures when the degeneracy is such as aids the prosperity of
the stirp.
Making this parenthetical reply to his parenthetical criticism I pass to
his discussion of this particular argument which he undertakes to dispose
of.
His _cheval de bataille_ is furnished him by the social insects--not a
fresh one, however, as might be supposed from the way in which he mounts
it. From time to time it has carried other riders, who have couched their
lances with fatal effects as they supposed. But I hope to show that no one
of them has unhorsed an antagonist, and that Professor Weismann fails to do
this just as completely as his predecessors. I am, indeed, not sorry that
he has afforded me the opportunity of criticising the general discussion
concerning the peculiarities of these interesting creatures, which it has
often seemed to me sets out with illegitimate assumptions. The supposition
always is that the specialities of structures and instincts in the unlike
classes of their communities, have arisen during the period in which the
communities have existed in something like their present forms. This cannot
be. It is doubtless true that association without differentiations of
classes may pre-exist for co-operative purposes, as among wolves, and as
among various insects which swarm under certain circumstances. Hence we may
suppose that there arise in some cases permanent swarms--that survival of
the fittest will establish these constant swarms where they are
advantageous. But admitting this, we have also to admit a gradual rise of
the associated state out of the solitary state. Wasps and bees present us
with gradations. If, then, we are to understand how the organized societies
have arisen, either out of the solitary state or out of undifferentiated
swarms, we must assume that the differences of structure and instinct among
the members of them arose little by little, as the social organization
arose little by little. Fortunately we are able to trace the greater part
of the process in the annually-formed communities of the common wasp; and
we shall recognize in it an all-important factor (ignored by Professor
Weismann) to which the phenomena, or at any rate the greater part of them,
are due.
But before describing the wasp's annual history, let me set down certain
observations made when, as a boy, I was given to angling, and, in July or
August, sometimes used for bait "wasp-grubs," as they were called. After
having had two or three days the combs or "cakes" of these, full of unfed
larvæ in all stages of growth, I often saw some of them devouring the edges
of their cells to satisfy their appetites; and saw others, probably the
most advanced in growth, which were spinning the little covering caps to
their cells, in preparation for assuming the pupa state. It is to be
inferred that if, after a certain stage of growth has been reached, the
food-supply becomes inadequate or is stopped altogether, the larva
undergoes its transformation prematurely; and, as we shall presently see,
this premature transformation has several natural sequences.
Let us return now to the wasp's family history. In the spring, a queen-wasp
or mother-wasp which has survived the winter, begins to make a small nest
containing four or more cells in which she lays eggs, and as fast as she
builds additional cells, she lays an egg in each. Presently, to these
activities, is added the feeding of the larvæ: one result being that the
multiplication of larvæ involves a restriction of the food that can be
given to each. If we suppose that the mother-wasp rears no more larvæ than
she can fully feed, there will result queens or mothers like herself,
relatively few in number. But if we suppose that, laying more numerous eggs
she produces more larvæ than she can fully feed, the result will be that
when these have reached a certain stage of growth, inadequate supply of
food will be followed by premature retirement and transformation into pupæ.
What will be the characters of the developed insects? The first effect of
arrested nutrition will be smaller size. This we find. A second effect will
be defective development of parts that are latest formed and least
important for the survival of the individual. Hence we may look for
arrested development of the reproductive organs--non-essential to
individual life. And this expectation is in accord with what we see in
animal development at large; for (passing over entirely sexless
individuals) we see that though the reproductive organs may be marked out
early in the course of development, they are not made fit for action until
after the structures for carrying on individual life are nearly complete.
The implication is, then, that an inadequately-fed and small larva will
become a sterile imago. Having noted this, let us pass to a remarkable
concomitant. In the course of development, organs are formed not alone in
the order of their original succession, but partly in the order of
importance and the share they have to take in adult activities--a change of
order called by Haeckel "heterochrony." Hence the fact that we often see
the maternal instinct precede the sexual instinct. Every little girl with
her doll shows us that the one may become alive while the other remains
dormant. In the case of wasps, then, premature arrest of development may
result in incompleteness of the sexual traits, along with completeness of
the maternal traits. What happens? Leave out the laying of eggs, and the
energies of the mother-wasp are spent wholly in building cells and feeding
larvæ, and the worker-wasp forthwith begins to spend its life in building
cells and feeding larvæ. Thus interpreting the facts, we have no occasion
to assume any constitutional difference between the eggs of worker-wasps
and the eggs of queens; and that, their eggs are not different we see,
first, in the fact that occasionally the worker-wasp is fertile and lays
drone-producing eggs, and we see secondly that (if in this respect they are
like the bees, of which, however, we have no proof) the larva of a
worker-wasp can be changed into the larva of a queen-wasp by special
feeding. But be this as it may, we have good evidence that the feeding
determines everything. Says Dr. Ormerod, in his _British Social Wasps_:--
"When the swarm is strong and food plentiful ... the well fed larvæ
develop into females, full, large, and overflowing with fat. There are
all gradations of size, from the large fat female to the smallest
worker.... The larger the wasp, the larger and better developed, as the
rule, are the female organs, in all their details. In the largest wasps,
which are to be the queens of another year, the ovaries differ to all
appearances in nothing but their size from those of the larger worker
wasps.... Small feeble swarms produce few or no perfect females; but in
large strong swarms they are found by the score." (pp. 248-9)
To this evidence add the further evidence that queens and workers pass
through certain parallel stages in respect of their maternal activities. At
first the queen, besides laying eggs, builds cells and feeds larvæ, but
after a time ceases to build cells, and feeds larvæ only, and eventually
doing neither one nor the other, only lays eggs, and is supplied with food
by the workers. So it is in part with the workers. While the members of
each successive brood, when in full vigour, build cells and feed larvæ,
by-and-by they cease to build cells, and only feed larvæ: the maternal
activities and instincts undergo analogous changes. In this case, then, we
are not obliged to assume that only by a process of natural selection can
the differences of structure and instinct between queens and workers be
produced. The only way in which natural selection here comes into play is
in the better survival of the families of those queens which made as many
cells, and laid as many eggs, as resulted in the best number of half-fed
larvæ, producing workers; since by a rapid multiplication of workers the
family is advantaged, and the ultimate production of more queens surviving
into the next year insured.
The differentiation of classes does not go far among the wasps, because the
cycle of processes is limited to a year, or rather to the few months of the
summer. It goes further among the hive-bees, which, by storing food,
survive from one year into the next. Unlike the queen-wasp, the queen-bee
neither builds cells nor gathers food, but is fed by the workers: egg
laying has become her sole business. On the other hand the workers,
occupied exclusively in building and nursing, have the reproductive organs
more dwarfed than they are in wasps. Still we see that the worker-bee
occasionally lays drone-producing eggs, and that, by giving extra nutriment
and the required extra space, a worker-larva can be developed into a
queen-larva. In respect to the leading traits, therefore, the same
interpretation holds. Doubtless there are subsidiary instincts which are
apparently not thus interpretable. But before it can be assumed that an
interpretation of another kind is necessary, it must be shown that these
instincts cannot be traced back to those pre-social types and semi-social
types which must have preceded the social types we now see. For
unquestionably existing bees must have brought with them from the
pre-social state an extensive endowment of instincts, and, acquiring other
instincts during the unorganized social state, must have brought these into
the present organized social state. It is clear, for instance, that the
cell-building instinct in all its elaboration was mainly developed in the
pre-social stage; for the transition from species building solitary cells
to those building combs is traceable. We are similarly enabled to account
for swarming as being an inheritance from remote ancestral types. For just
in the same way that, with under-feeding of larvæ, there result individuals
with imperfectly developed reproductive systems, so there will result
individuals with imperfect sexual instincts; and just as the imperfect
reproductive system partially operates upon occasion, so will the imperfect
sexual instinct. Whence it will result that on the event which causes a
queen to undertake a nuptial flight which is effectual, the workers may
take abortive nuptial flights: so causing a swarm.
And here, before going further, let us note an instructive class of facts
related to the class of facts above set forth. Summing up, in a chapter on
"The Determination of Sex," an induction from many cases, Professor Geddes
and Mr. Thompson remark that "such conditions as deficient or abnormal
food," and others causing "preponderance of waste over repair ... tend to
result in production of males;" while "abundant and rich nutrition" and
other conditions which "favour constructive processes ... result in the
production of females."[118] Among such evidences of this as immediately
concern us, are these:--J. H. Fabre found that in the nests of _Osmia
tricornis_, eggs at the bottom, first laid, and accompanied by much food,
produced females, while those at the top, last laid, and accompanied by
one-half or one-third the quantity of food, produced males,[119] Huber's
observations on egg-laying by the honey-bee, show that in the normal course
of things, the queen lays eggs of workers for eleven months, and only then
lays eggs of drones: that is, when declining nutrition or exhaustion has
set in. Further, we have the above-named fact, shown by wasps and bees,
that when workers lay eggs these produce drones only.[120] Special
evidence, harmonizing with general evidence, thus proves that among the
social insects the sex is determined by degree of nutrition while the egg
is being formed. See then how congruous this evidence is with the
conclusion above drawn; for it is proved that after an egg, predetermined
as a female, has been laid, the character of the produced insect as a
perfect female or imperfect female is determined by the nutrition of the
larva. _That is, one set of differences in structures and instincts is
determined by nutrition before the egg is laid, and a further set of
differences in structures and instincts is determined by nutrition after
the egg is laid._
We come now to the extreme case--that of the ants. Is it not probable that
the process of differentiation has been similar? There are sundry reasons
for thinking so. With ants as with wasps and bees--the workers occasionally
lay eggs; and an ant-community can, like a bee-community, when need be,
produce queens out of worker-larvæ: presumably in the same manner by extra
feeding. But here we have to add special evidence of great significance.
For observe that the very facts concerning ants, which Professor Weismann
names as exemplifying the formation of the worker type by selection, serve,
as in the case of wasps, to exemplify its formation by arrested nutrition.
He says that in several species the egg-tubes in the ovaries show
progressive decrease in number; and this, like the different degrees of
arrest in the ovaries of the worker-wasps, indicates arrest of
larva-feeding at different stages. He gives cases showing that, in
different degrees, the eyes of workers are less developed in the number of
their facets than those of the perfect insects; and he also refers to the
wings of workers as not being developed: remarking, however, that the
rudiments of their wings show that the ancestral forms had wings. Are not
these traits also results of arrested nutrition? Generally among insects
the larvæ are either blind or have but rudimentary eyes; that is to say,
visual organs are among the latest organs to arise in the genesis of the
perfect organism. Hence early arrest of nutrition will stop formation of
these, while various more ancient structures have become tolerably
complete. Similarly with wings. Wings are late organs in insect phylogeny,
and therefore will be among those most likely to abort where development is
prematurely arrested. And both these traits will, for the same reason,
naturally go along with arrested development of the reproductive system.
Even more significant, however, is some evidence assigned by Mr. Darwin
respecting the caste-gradations among the driver ants of West Africa. He
says:--
"But the most important fact for us is, that, though the workers can be
grouped into castes of different sizes, yet they graduate insensibly into
each other, as does the widely-different structure of their jaws."[121]
"Graduate insensibly," he says; implying that there are very numerous
intermediate forms. This is exactly what is to be expected if arrest of
nutrition be the cause; for unless the ants have definite measures,
enabling them to stop feeding at just the same stages, it must happen that
the stoppage of feeding will be indefinite; and that, therefore, there will
be all gradations between the extreme forms--"insensible gradations," both
in size and in jaw-structure.
In contrast with this interpretation, consider now that of Professor
Weismann. From whichever of the two possible suppositions he sets out, the
result is equally fatal. If he is consistent, he must say that each of
these intermediate forms of workers must have its special set of
"determinants," causing its special set of modifications of organs; for he
cannot assume that while perfect females and the extreme types of workers
have their different sets of determinants, the intermediate types of
workers have not. Hence we are introduced to the strange conclusion that
besides the markedly-distinguished sets of determinants there must be, to
produce these intermediate forms, many other sets slightly distinguished
from one another--a score or more kinds of germ-plasm in addition to the
four chief kinds. Next comes an introduction to the still stranger
conclusion, that these numerous kinds of germ-plasm, producing these
numerous intermediate forms, are not simply needless but injurious--produce
forms not well fitted for either of the functions discharged by the extreme
forms: the implication being that natural selection has originated these
disadvantageous forms! If to escape from this necessity for suicide,
Professor Weismann accepts the inference that the differences among these
numerous intermediate forms are caused by arrested feeding of the larvæ at
different stages, then he is bound to admit that the differences between
the extreme forms, and between these and perfect females, are similarly
caused. But if he does this, what becomes of his hypothesis that the
several castes are constitutionally distinct, and result from the operation
of natural selection? Observe, too, that his theory does not even allow him
to make this choice; for we have clear proof that unlikenesses among the
forms of the same species cannot be determined this way or that way by
differences of nutrition. English greyhounds and Scotch greyhounds do not
differ from one another so much as do the Amazon-workers from the inferior
workers, or the workers from the queens. But no matter how a pregnant
Scotch greyhound is fed, or her pups after they are born, they cannot be
changed into English greyhounds: the different germ-plasms assert
themselves spite of all treatment. But in these social insects the
different structures of queens and workers _are_ determinable by
differences of feeling. Therefore the production of their various castes
does not result from the natural selection of varying germ-plasm.
Before dealing with Professor Weismann's crucial case--that co-adaptation
of parts, which, in the soldier-ants, has, he thinks, arisen without
inheritance of acquired characters--let me deal with an ancillary case
which he puts forward as explicable by "panmixia alone." This is the
"degeneration, in the warlike Amazon-ants, of the instinct to search for
food."[122] Let us first ask what have been the probable antecedents of
these Amazon-ants; for, as I have above said, it is absurd to speculate
about the structures and instincts the species possesses in its existing
organized social state without asking what structures and instincts it
brought with it from its original solitary state and its unorganized social
state. From the outset these ants were predatory. Some variety of them led
to swarm--probably at the sexual season--did not again disperse so soon as
other varieties. Those which thus kept together derived advantages from
making simultaneous attacks on prey, and prospered accordingly. Of
descendants the varieties which carried on longest the associated state
prospered most; until, at length, the associated state became permanent.
All which social progress took place while there existed only perfect males
and females. What was the next step? Ants utilize other insects, and, among
other ways of doing this, sometimes make their nests where there are useful
insects ready to be utilized. Giving an account of certain New Zealand
species of _Tetramorium_, Mr. W. W. Smith says they seek out underground
places where there are "root-feeding aphides and coccids," which they begin
to treat as domestic animals; and further he says that when, after the
pairing season, new nests are being formed, there are "a few ants of both
sexes ... from two up to eight or ten."[123] Carrying with us this fact as
a key, let us ask what habits will be fallen into by the conquering species
of ants. They, too, will seek places where there are creatures to be
utilized; and, finding it profitable, will invade the habitations not of
defenceless creatures only, but of creatures whose powers of defence are
inadequate--weaker species of their own order. A very small modification
will affiliate their habits on habits of their prototypes. Instead of being
supplied with sweet substance excreted by the aphides they are supplied
with sweet substance by the ants among which they parasitically settle
themselves. How easily the subjugated ants may fall into the habit of
feeding them, we shall see on remembering that already they feed not only
larvæ but adults--individuals bigger than themselves. And that attentions
kindred to these paid to parasitic ants may be established without
difficulty, is shown us by the small birds which continue to feed a young
cuckoo in their nest when it has outgrown them. This advanced form of
parasitism grew up while there were yet only perfect males and females, as
happens in the initial stage with these New Zealand ants. What further
modifications of habits were probably then acquired? From the practice of
settling themselves where there already exist colonies of aphides, which
they carry about to suitable places in the nest, like _Tetramorium_, other
ants pass to the practice of making excursions to get aphides, and putting
them in better feeding places where they become more productive of
saccharine matter. By a parallel step these soldier-ants pass from the
stage of settling themselves among other ants which feed them, to the stage
of fetching the pupæ of such ants to the nest: a transition like that which
occurs among slave-making human beings. Thus by processes analogous to
those we see going on, these communities of slave-making ants may be
formed. And since the transition from an unorganized social state to a
social state characterized by castes, must have been gradual, there must
have been a long interval during which the perfect males and females of
these conquering ants could acquire habits and transmit them to progeny. A
small modification accounts for that seemingly-strange habit which
Professor Weismann signalizes. For if, as is observed, those ants which
keep aphides solicit them to excrete a supply of ant-food by stroking them
with the antennæ, they come very near to doing that which Professor
Weismann says the soldier-ants do towards a worker--"they come to it and
beg for food:" the food being put into their mouths in this last case as
almost or quite in the first. And evidently this habit of passively
receiving food, continued through many generations of perfect males and
females, may result in such disuse of the power of self-feeding that this
is eventually lost. The behaviour of young birds, during, and after, their
nest-life, gives us the clue. For a week or more after they are full-grown
and fly about with their parents, they may be seen begging for food and
making no efforts to recognize and pick up food for themselves. If,
generation after generation, feeding of them in full measure continued,
they would not learn to feed themselves: the perceptions and instincts
implied in self-feeding would be later and later developed, until, with
entire disuse of them, they would disappear altogether by inheritance. Thus
self-feeding may readily have ceased among these soldier-ants before the
caste-organization arose among them.
With this interpretation compare the interpretation of Professor Weismann.
I have before protested against arguing in abstracts without descending to
concretes. Here let us ask what are the particular changes which the
alleged explanation by survival of the fittest involves. Suppose we make
the very liberal supposition that an ant's central ganglion bears to its
body the same ratio as the human brain bears to the human body--say,
one-fortieth of its weight. Assuming this, what shall we assume to be the
weight of those ganglion-cells and fibres in which are localized the
perceptions of food and the suggestion to take it? Shall we say that these
amount to one-tenth of the central ganglion? This is a high estimate
considering all the impressions which this ganglion has to receive, and all
the operations which it has to direct. Still we will say one-tenth. Then it
follows that this portion of nervous substance is one-400th of the weight
of its body. By what series of variations shall we say that it is reduced
from full power to entire incapacity? Shall we say five? This is a small
number to assume. Nevertheless we will assume it. What results? That the
economy of nerve-substance achieved by each of these five variations will
amount to one-2000th of the entire mass. Making these highly favourable
assumptions, what follows:--The queen-ant lays eggs that give origin to
individuals in each of which there is achieved an economy in
nerve-substance of one-2000th of its weight; and the implication of the
hypothesis is that such an economy will so advantage this ant-community
that in the competition with other ant-communities it will conquer. For
here let me recall the truth before insisted upon, that natural selection
can operate only on those variations which appreciably benefit the stirp.
Bearing in mind this requirement, is any one now prepared to say that
survival of the fittest can cause this decline of the self-feeding
faculty?[124]
Not limiting himself to the Darwinian interpretation, however, Professor
Weismann says that this degradation may be accounted for by "panmixia
alone." Here I will not discuss the adequacy of this supposed cause, but
will leave it to be dealt with by implication a few pages in advance, where
the general hypothesis of panmixia will be reconsidered.
And now, at length, we are prepared for dealing with Professor Weismann's
crucial case--with his alleged disproof that co-adaptation of co-operative
parts results from inheritance of acquired characters, because in the case
of the Amazon-ants, it has arisen where the inheritance of acquired
characters is impossible. For after what has been said, it will be manifest
that the whole question is begged when it is assumed that this
co-adaptation has arisen since there existed among these ants an organized
social state. Unquestionably this organized social state pre-supposes a
series of modifications through which it has been reached. It follows,
then, that there can be no rational interpretation without a preceding
inquiry concerning that earlier state in which there were no castes, but
only males and females. What kinds of individuals were the ancestral
ants--at first solitary, and then semi-social? They must have had marked
powers of offence and defence. Of predacious creatures, it is the more
powerful which form societies, not the weaker. Instance human races.
Nations originate from the relatively warlike tribes, not from the
relatively peaceful tribes. Among the several types of individuals forming
the existing ant community, to which, then, did the ancestral ants bear the
greatest resemblance? They could not have been like the queens, for these,
now devoted to egg-laying, are unfitted for conquest. They could not have
been like the inferior class of workers, for these, too, are inadequately
armed and lack strength. Hence they must have been most like these
Amazon-ants or soldier-ants, which now make predatory excursions--which now
do, in fact, what their remote ancestors did. What follows? Their
co-adapted parts have not been produced by the selection of variations
within the ant-community, such as we now see it. They have been inherited
from the pre-social and early social types of ants, in which the
co-adaptation of parts had been effected by inheritance of acquired
characters. It is not that the soldier-ants have gained these traits; it is
that the other castes have lost them. Early arrest of development causes
absence of them in the inferior workers; and from the queens they have
slowly disappeared by inheritance of the effects of disuse. For, in
conformity with ordinary facts of development, we may conclude that in a
larva which is being so fed as that the development of the reproductive
organs is becoming pronounced, there will simultaneously commence arrest in
the development of those organs which are not to be used. There are
abundant proofs that along with rapid growth of some organs others abort.
And if these inferences are true, then Professor Weismann's argument falls
to the ground. Nay, it falls to the ground even if conclusions so definite
as these be not insisted upon; for before he can get a basis for his
argument he must give good reasons for concluding that these traits of the
Amazon-ants have _not_ been inherited from remote ancestors.
One more step remains. Let us grant him his basis, and let us pass from the
above negative criticism to a positive criticism. As before, I decline to
follow the practice of talking in abstracts instead of in concretes, and
contend that, difficult as it may be to see how natural selection has in
all cases operated, we ought, at any rate, to trace out its operation
whenever we can, and see where the hypothesis lands us. According to
Professor Weismann's admission, for production of the Amazon-ant by natural
selection, "_many parts must have varied simultaneously and in harmony with
one another_;"[125] and he names as such, larger jaws, muscles to move
them, larger head, and thicker chitin for it, bigger nerves for the
muscles, bigger motor centres in the brain, and, for the support of the big
head, strengthening of the thorax, limbs, and skeleton generally. As he
admits, all these parts must have varied simultaneously in due proportion
to one another. What must have been the proximate causes of their
variations? They must have been variations in what he calls the
"determinants." He says:--
"We have, however, to deal with the transmission of parts which are
_variable_ and this necessitates the assumption that just as many
independent and variable parts exist in the germ-plasm as are present in
the fully formed organism."[126]
Consequently to produce simultaneously these many variations of parts,
adjusted in their sizes and shapes, there must have simultaneously arisen a
set of corresponding variations in the "determinants" composing the
germ-plasm. What made them simultaneously vary in the requisite ways?
Professor Weismann will not say that there was somewhere a foregone
intention. This would imply supernatural agency. He makes no attempt to
assign a physical cause for these simultaneous appropriate variations in
the determinants: an adequate physical cause being inconceivable. What,
then, remains as the only possible interpretation? Nothing but _a
fortuitous concourse of variations_; reminding us of the old "fortuitous
concourse of atoms." Nay, indeed, it is the very same thing. For each of
the "determinants," made up of "biophors," and these again of
protein-molecules, and these again of simpler chemical molecules, must have
had its molecular constitution changed in the required way; and the
molecular constitutions of all the "determinants," severally modified
differently, but in adjustment to one another, must have been thus modified
by "a fortuitous concourse of atoms." Now if this is an allowable
supposition in respect of the "determinants," and the varying organs
arising from them, why is it not an allowable supposition in respect of the
organism as a whole? Why not assume "a fortuitous concourse of atoms" in
its broad, simple form? Nay, indeed, would not this be much the easier? For
observe, this co-adaptation of numerous co-operative parts is not achieved
by one set of variations, but is achieved gradually by a series of such
sets. That is to say, the "fortuitous concourse of atoms" must have
occurred time after time in appropriate ways. We have not one miracle, but
a series of miracles!
* * * * *
Of the two remaining points in Professor Weismann's first article which
demand notice, one concerns his reply to my argument drawn from the
distribution of tactual discriminativeness. In what way does he treat this
argument? He meets it by an argument derived from hypothetical
evidence--not actual evidence. Taking the case of the tongue-tip, I have
carefully inquired whether its extreme power of tactual discrimination can
give any life-saving advantage in moving about the food during mastication,
in detecting foreign bodies in it, or for purposes of speech; and have, I
think, shown that the ability to distinguish between points one
twenty-fourth of an inch apart is useless for such purposes. Professor
Weismann thinks he disposes of this by observing that among the apes the
tongue is used as an organ of touch. But surely a counter-argument
equivalent in weight to mine should have given a case in which power to
discriminate between points one twenty-fourth of an inch apart instead of
one-twentieth of an inch apart (a variation of one-sixth) had a life-saving
efficacy; or, at any rate, should have suggested such a case. Nothing of
the kind is done or even attempted. But now note that his reply, accepted
even as it stands, is suicidal. For what has the trusted process of
panmixia been doing ever since the human being began to evolve from the
ape? Why during thousands of generations has not the nervous structure
giving this extreme discriminativeness dwindled away? Even supposing it had
been proved of life-saving efficacy to our simian ancestors, it ought,
according to Professor Weismann's own hypothesis, to have disappeared in
us. Either there was none of the assumed special capacity in the ape's
tongue, in which case his reply fails, or panmixia has not operated, in
which case his theory of degeneracy fails.
All this, however, is but preface to the chief answer. The argument drawn
from the case of the tongue-tip, with which alone Professor Weismann deals,
is but a small part of my argument, the remainder of which he does not
attempt to touch--does not even mention. Had I never referred to the
tongue-tip at all, the various contrasts in discriminativeness which I have
named, between the one extreme of the forefinger-tip and the other extreme
of the middle of the back, would have abundantly sufficed to establish my
case--would have sufficed to show the inadequacy of natural selection as a
key and the adequacy of the inheritance of acquired characters.
It seems to me, then, that judgment must go against him by default.
Practically he leaves the matter standing just where it did.[127]
The other remaining point concerns the vexed question of panmixia.
Confirming the statement of Dr. Romanes, Professor Weismann says that I
have misunderstood him. Already (_Contemporary Review_, May, 1893, p. 758,
and Reprint, p. 66) I have quoted passages which appeared to justify my
interpretation, arrived at after much seeking.[128] Already, too, in this
review (July, 1893, p. 54) I have said why I did not hit upon the
interpretation now said to be the true one: I never supposed that any one
would assume, without assigned cause, that (apart from the excluded
influence of disuse) the _minus_ variations of a disused organ are greater
than the _plus_ variations. This was a tacit challenge to produce reasons
for the assumption. Professor Weismann does not accept the challenge, but
simply says:--"In my opinion all organs are maintained at the height of
their development only through uninterrupted selection" (p. 332): in the
absence of which they decline. Now it is doubtless true that as a
naturalist he may claim for his "opinion" a relatively great weight. Still,
in pursuance of the methods of science, it seems to me that something more
than an opinion is required as the basis of a far-reaching theory.[129]
Though the counter-opinion of one who is not a naturalist (as Professor
Weismann points out) may be of relatively small value, yet I must here
again give it, along with a final reason for it. And this reason shall be
exhibited, not in a qualitative form, but in a quantitative form. Let us
quantify the terms of the hypothesis by weights; and let us take as our
test case the rudimentary hind-limbs of the whale. Zoologists are agreed
that the whale has been evolved from a mammal which took to aquatic habits,
and that its disused hind-limbs have gradually disappeared. When they
ceased to be used in swimming, natural selection played a part--probably an
important part--in decreasing them; since, being then impediments to
movement through the water, they diminished the attainable speed. It may
be, too, that for a period after disappearance of the limbs beneath the
skin, survival of the fittest had still some effect. But during the latter
stages of the process it had no effect; since the rudiments caused no
inconvenience and entailed no appreciable cost. Here, therefore, the cause,
if Professor Weismann is right, must have been panmixia. Dr. Struthers,
Professor of Anatomy at Aberdeen, whose various publications show him to be
a high, if not the highest, authority on the anatomy of these great
cetaceans, has kindly taken much trouble in furnishing me with the needful
data, based upon direct weighing and measuring and estimation of specific
gravity. In the Black Whale (_Balænoptera borealis_) there are no rudiments
of hind-limbs whatever: rudiments of the pelvic bones only remain. A sample
of the Greenland Right Whale, estimated to weigh 44,800 lbs., had femurs
weighing together 3½ ozs.; while a sample of the Razor-back Whale
(_Balænoptera musculus_), 50 feet long, and estimated to weigh 56,000 lbs.,
had rudimentary femurs weighing together one ounce; so that these vanishing
remnants of hind-limbs weighed but one-896,000th part of the animal. Now in
considering the alleged degeneration by panmixia, we have first to ask why
these femurs must be supposed to have varied in the direction of decrease
rather than in the direction of increase. During its evolution from the
original land-mammal, the whale has grown enormously, implying habitual
excess of nutrition. Alike in the embryo and in the growing animal, there
must have been a chronic plethora. Why, then, should we suppose these
rudiments to have become smaller? Why should they not have enlarged by
deposit in them of superfluous materials? But let us grant the unwarranted
assumption of predominant _minus_ variations. Let us say that the last
variation was a reduction of one-half--that in some individuals the joint
weight of the femurs was suddenly reduced from two ounces to one ounce--a
reduction of one-900,000th of the creature's weight. By inter-crossing with
those inheriting the variation, the reduction, or a part of the reduction,
was made a trait of the species. Now, in the first place, a necessary
implication is that this _minus_ variation was maintained in posterity. So
far from having reason to suppose this, we have reason to suppose the
contrary. As before quoted, Mr. Darwin says that "unless carefully
preserved by man," "any particular variation would generally be lost by
crossing, reversion, and the accidental destruction of the varying
individuals."[130] And Mr. Galton, in his essay on "Regression towards
Mediocrity,"[131] contends that not only do deviations of the whole
organism from the mean size tend to thus disappear, but that deviations in
its components do so. Hence the chances are against such _minus_ variation
being so preserved as to affect the species by panmixia. In the second
place, supposing it to be preserved, may we reasonably assume that, by
inter-crossing, this decrease, amounting to about a millionth part of the
creature's weight, will gradually affect the constitutions of all
Razor-back Whales distributed over the Arctic seas and the North Atlantic
Ocean, from Greenland to the Equator? Is this a credible conclusion? For
three reasons, then, the hypothesis must be rejected.
Thus, the only reasonable interpretation is the inheritance of acquired
characters. If the effects of use and disuse, which are known causes of
change in each individual, influence succeeding individuals--if
functionally-produced modifications of structure are transmissible, as well
as modifications of structure otherwise arising--then this reduction of the
whale's hind limbs to minute rudiments is accounted for. The cause has been
unceasingly operative on all individuals of the species ever since the
transformation began.
In one case see all. If this cause has thus operated on the limbs of the
whale, it has thus operated in all creatures on all parts having active
functions.
* * * * *
At the outset I intimated that I must limit my replies to those arguments
of Professor Weismann which are contained in his first article. That those
contained in his second might be dealt with no less effectually, did time
and space permit, is manifest to me; but about the probability of this the
reader must form his own judgment. My replies thus far may be summed up as
follows:--
Professor Weismann says he has disproved the conclusion that degeneration
of the little toe has resulted from inheritance of acquired characters. But
his reasoning fails against an interpretation he overlooks. A profound
modification of the hind limbs and their appendages must have taken place
during the transition from arboreal habits to terrestrial habits; and
dwindling of the little toe is an obvious consequence of disuse, at the
same time that enlargement of the great toe is an obvious consequence of
increased use.
The entire argument based on the unlike forms and instincts presented by
castes of social insects is invalidated by an omission. Until probable
conclusions are reached respecting the characters which such insects
brought with them into the organized social state, no valid inferences can
be drawn respecting characters developed during that state.
A further large error of interpretation is involved in the assumption that
the different caste-characters are transmitted to them in the eggs laid by
the mother insect. While we have evidence that the unlike structures of the
sexes are determined by nutrition of the germ before egg-laying, we have
evidence that the unlike structures of classes are caused by unlikenesses
of nutrition of the larvæ. That these varieties of forms do not result from
varieties of germ-plasms, is demonstrated by the fact that where there are
varieties of germ-plasms, as in varieties of the same species of mammal, no
deviations in feeding prevent display of their structural results.
For such caste-modifications as those of the Amazon-ants, which are unable
to feed themselves, there is a feasible explanation other than Professor
Weismann's. The relation of common ants to their domestic animals--aphides
and coccids--which yield them food on solicitation, does not differ widely
from this relation between these Amazon-ants and their domestic
animals--the slave-ants. And the habit of being fed, contracted during the
first stages of their parasitic life, when there were perfect males and
females, may, during that stage, have become established by inheritance.
Meanwhile the opposed interpretation--that this incapacity has resulted
from the selection of those ant-communities the queens of which laid eggs
that had so varied as to entail this incapacity--implies that a scarcely
appreciable economy of nerve-matter advantaged the stirp so greatly as to
cause it to spread more than other stirps: an incredible supposition.
As the outcome of these alternative interpretations we saw that the
argument respecting the co-adaptation of co-operative parts, which
Professor Weismann thinks is furnished to him by the Amazon-ants,
disappears. The ancestral ants were conquering ants. These founded the
communities; and hence those members of the present communities which are
most like them are the Amazon-ants. If so, the co-adaptation of the
co-operative parts was effected by inheritance during the solitary and
semi-social stages. Even were there no such solution, the opposed solution
will be unacceptable. These simultaneous appropriate variations of the
co-operative parts in sizes, shapes, and proportions, are supposed to be
effected by simultaneous variations in the "determinants" of the
germ-plasms; and in the absence of an assigned physical cause, this implies
a fortuitous concourse of appropriate variations, which carries us back to
a "fortuitous concourse of atoms." This may just as well be extended to the
entire organism. The old hypothesis of special creations is more consistent
and comprehensible.
To rebut my inference drawn from the distribution of discriminativeness,
Professor Weismann uses not an argument but the blank form of an argument.
The ability to discriminate one twenty-fourth of an inch by the tongue-tip
_may_ have been useful to the ape: no conceivable use being even suggested.
And then the great body of my argument derived from the distribution of
discriminativeness over the skin, which amply suffices, is wholly ignored.
The tacit challenge I gave to name some facts in support of the hypothesis
of panmixia--or even a solitary fact--is passed by. It remains a pure
speculation having no basis but Professor Weismann's "opinion." When from
the abstract statement of it we pass to a concrete test, in the case of the
whale, we find that it necessitates an unproved and improbable assumption
respecting _plus_ and _minus_ variations; that it ignores the unceasing
tendency to reversion; and that it implies an effect out of all proportion
to the cause.
It is curious what entirely opposite conclusions men may draw from the same
evidence. Professor Weismann thinks he has shown that the "last bulwark of
the Lamarckian principle is untenable." Most readers will hold with me that
he is, to use the mildest word, premature in so thinking. Contrariwise my
impression is that he has not shown either this bulwark or any other
bulwark to be untenable; but rather that while his assault has failed it
has furnished opportunity for strengthening sundry of the bulwarks.
IV.
Among those who follow a controversy to its close, not one in a hundred
turns back to its beginning to see whether its chief theses have been dealt
with. Very often the leading arguments of one disputant, seen by the other
to be unanswerable, are quietly ignored, and attention is concentrated on
subordinate arguments to which replies, actually or seemingly valid, can be
made. The original issue is thus commonly lost sight of.
More than once I have pointed out that, as influencing men's views about
Education, Ethics, Sociology, and Politics, the question whether acquired
characters are inherited is the most important question before the
scientific world. Hence I cannot allow the discussion with Professor
Weismann to end in so futile a way as it will do if no summary of results
is made. Here, therefore, I propose to recapitulate the whole case in
brief. Primarily my purpose is to recall certain leading propositions
which, having been passed by unnoticed, remain outstanding. I will turn, in
the second place, to such propositions as have been dealt with; hoping to
show that the replies given are invalid, and consequently that these
propositions also remain outstanding.
But something beyond a summing-up is intended. A few pages at the close
will be devoted to setting forth new evidence which has come to light since
the controversy commenced--evidence which many will think sufficient in
itself to warrant a positive conclusion.
* * * * *
The fact that the tip of the fore finger has thirty times the power of
discrimination possessed by the middle of the back, and that various
intermediate degrees of discriminative power are possessed by various parts
of the skin, was set down as a datum for my first argument. The causes
which might be assigned for these remarkable contrasts were carefully
examined under all their aspects. I showed in detail that the contrasts
could not in any way be accounted for by natural selection. I further
showed that no interpretation of them is afforded by the alleged process of
panmixia: this has no _locus standi_ in the case. Having proved
experimentally, that ability of the fingers to discriminate is increased by
practice, and having pointed out that gradations of discriminativeness in
different parts correspond with gradations in the activities of the parts
as used for tactual exploration, I argued that these contrasts have arisen
from the organized and inherited effects of tactual converse with
surrounding things, varying in its degrees according to the positions of
the parts--in other words, that they are due to the inheritance of acquired
characters. As a crowning proof I instanced the case of the tongue-tip,
which has twice the discriminativeness of the forefinger-tip: pointing out
that consciously, or semi-consciously, or unconsciously, the tongue-tip is
perpetually exploring the inner surfaces of the teeth.
Singling out this last case, Professor Weismann made, or rather adopted
from Dr. Romanes, what professed to be a reply but was nothing more than
the blank form of a reply. It was said that though this extreme
discriminativeness of the tongue-tip is of no use to mankind, it may have
been of use to certain ancestral _primates_. No evidence of any such use
was given; no imaginable use was assigned. It was simply suggested that
there perhaps was a use.
In my rejoinder, after indicating the illusory nature of this proceeding
(which is much like offering a cheque on a bank where no assets have been
deposited to meet it), I pointed out that had the evidence furnished by the
tongue tip never been mentioned, the evidence otherwise furnished amply
sufficed. I then drew attention to the fact that this evidence had been
passed over, and tacitly inquired why.
No reply.[132]
* * * * *
In his essay on "The All-Sufficiency of Natural Selection," Professor
Weismann set out, not by answering one of the arguments I had used, but by
importing into the discussion an argument used by another writer, which it
was easy to meet. It had been contended that the smallness and deformity of
the little toe are consequent upon the effects of boot-pressure, inherited
from generation to generation. To this Professor Weismann made the
sufficient reply that the fusion of the phalanges and otherwise degraded
structure of the little toe, exist among peoples who go barefoot.
In my "Rejoinder" I said that though the inheritance of acquired characters
does not explain this degradation in the way alleged, it explains it in a
way which Professor Weismann overlooks. The cause is one which has been
operating ever since the earliest anthropoid creatures began to decrease
their life in trees and increase their life on the earth's surface. The
mechanics of walking and running, in so far as they concern the question at
issue, were analyzed; and it was shown that effort is economized and
efficiency increased in proportion as the stress is thrown more and more on
the inner digits of the foot and less and less on the outer digits. So that
thus the foot furnishes us simultaneously with an instance of increase from
use and of decrease from disuse; a further disproof being yielded of the
allegation that co-operative parts vary together, since we have here
co-operative parts of which one grows while the other dwindles.
I ended by pointing out that, so far from strengthening his own case,
Professor Weismann had, by bringing into the controversy this changed
structure of the foot, given occasion for strengthening the opposite case.
No reply.
* * * * *
We come now to Professor Weismann's endeavour to disprove my second
thesis--that it is impossible to explain by natural selection alone the
co-adaptation of co-operative parts. It is thirty years since this was set
forth in _The Principles of Biology_. In § 166 I instanced the enormous
horns of the extinct Irish elk, and contended that in this, and in kindred
cases, where for the efficient use of some one enlarged part many other
parts have to be simultaneously enlarged, it is out of the question to
suppose that they can have all spontaneously varied in the required
proportions. In "The Factors of Organic Evolution," by way of enforcing
this argument, which had, so far as I know, never been met, I dwelt upon
the aberrant structure of the giraffe. And then, in the essay which
initiated this controversy, I brought forward yet a third case--that of an
animal which, previously accustomed only to walking, acquires the power of
leaping.
In the first of his articles in the _Contemporary Review_ (September,
1893), Professor Weismann made no direct reply, but he made an indirect
reply. He did not attempt to show how there could have taken place in the
stag the "harmonious variation of the different parts that co-operate to
produce one physiological result" (p. 311); but he contended that such
harmonious variation _must_ have taken place, because the like has taken
place in "the neuters of state-forming insects"--"animal forms which do not
reproduce themselves, but are always propagated anew by parents which are
unlike them" (p. 313), and which therefore cannot have transmitted acquired
characters. Singling out those soldier-neuters which exist among certain
kinds of ants, he described (p. 318) the many co-ordinated parts required
to make their fighting organs efficient. He then argued that the required
simultaneous changes can "only have arisen by a selection of the
parent-ants dependent on the fact that those parents which produced the
best workers had always the best prospect of the persistence of their
colony. No other explanation is conceivable; _and it is just because no
other explanation is conceivable, that it is necessary for us to accept the
principle of natural selection_" (pp. 318-9).
[This passage initiated a collateral controversy, which, as continually
happens, has greatly obscured the primary controversy. It became a question
whether these forms of neuter insects have arisen as Professor Weismann
assumes, or whether they have arisen from arrested development consequent
upon innutrition. To avoid entanglements I must for the present pass over
this collateral controversy, intending to resume it presently, when the
original issues have been dealt with.]
No one will suspect me of thinking that the inconceivability of the
negation is not a valid criterion, since, in "The Universal Postulate,"
published in the _Westminster Review_ in 1852 and afterwards in _The
Principles of Psychology_, I contended that it is the ultimate test of
truth. But then in every case there has to be determined the question--Is
the negation inconceivable; and in assuming that it is so in the case
named, lies the fallacy of the above-quoted passage. The three separate
ways in which I dealt with this position of Professor Weismann are as
follows:--
If we admit the assumption that the form of the soldier-ant has been
developed since the establishment of the organized ant-community in which
it exists, Professor Weismann's assertion that no other process than that
which he alleges is conceivable, is true. But I pointed out that this
assumption is inadmissible; and that no valid conclusion respecting the
genesis of the soldier-ant can be drawn without postulating either the
ascertained, or the probable, structure of those pre-social, or
semi-social, ants from which the organized social ants have descended. I
went on to contend that the pre-social type must have been a conquering
type, and that therefore in all probability the soldier-ants represent most
nearly the structures of those ancestral ants which existed when the
society had perfect males and females and could transmit acquired
characters, while the other members of the existing communities are
degraded forms of the type.
No reply.
A further argument I used was that where there exist different castes among
the neuter-ants, as those seen in the soldiers and workers of the Driver
ants of West Africa, "they graduate insensibly into each other" alike in
their sizes and in their structures; and that Professor Weismann's
hypothesis implies a special set of "determinants" for each intermediate
form. Or if he should say that the intermediate forms result from mixtures
of the determinants of the two extreme forms, there still remains the
further difficulty that natural selection has maintained, for innumerable
generations, these intermediate forms which are injurious deviations from
the useful extreme forms.
No reply.
One further reason--fatal it seems to me--was urged in bar of his
interpretation. No physical cause has been, or can be, assigned, why in the
germ-plasm of any particular queen-ant, the "determinants" initiating these
various co-operative organs, all simultaneously vary in fitting ways and
degrees, and still less why there occur such co-ordinated variations
generation after generation, until by their accumulated results these
efficient co-operative structures have been evolved. I pointed out that in
the absence of any assigned or assignable physical cause, it is necessary
to assume a fortuitous concurrence of favourable variations, which means "a
fortuitous concourse of atoms;" and that it would be just as rational, and
much more consistent, to assume that the structure of the entire organism
thus resulted.
No reply.
* * * * *
It is reasonable to suspect that Professor Weismann recognized these
difficulties as insuperable, for, in his Romanes Lecture on "The Effect of
External Influences upon Development," instead of his previous indirect
reply, he makes a direct reply. Reverting to the stag and its enlarging
horns, he alleges a process by which, as he thinks, we may understand how,
by variation and selection, all the bones and muscles of the neck, of the
thorax, and of the fore-legs, are step by step adjusted in their sizes to
the increasing sizes of the horns. He ascribes this harmonization to the
internal struggle for nutriment, and that survival of the fittest which
takes place among the parts of an organism: a process which he calls
"_intra-individual_-selection, or more briefly--_intra-selection_" (p. 12).
"Wilhelm Roux has given an explanation of the cause of these wonderfully
fine adaptations by applying the principle of selection to the parts of
the organism. Just as there is a struggle for survival among the
individuals of a species, and the fittest are victorious, so also do even
the smallest living particles contend with one another, and those that
succeed best in securing food and place grow and multiply rapidly, and so
displace those that are less suitably equipped" (p. 12).[133]
That I do not explain as he does the co-adaptation of co-operative parts,
Professor Weismann ascribes to my having overlooked this "principle of
intra-selection"--an unlucky supposition, as we see. But I do not think
that when recognizing it a generation ago, I should have seen its relevancy
to the question at issue, had that issue then been raised, and I certainly
do not see it now. Full reproduction of Professor Weismann's explanation is
impracticable, for it occupies several pages, but here are the essential
sentences from it:--
"The great significance of intra-selection appears to me not to depend on
its producing structures that are directly transmissible,--it cannot do
that,--but rather consists in its causing a development of the
germ-structure, acquired by the selection of individuals, which will be
suitable to varying conditions.... We may therefore say that
intra-selection effects the adaptation of the individual to its chance
developmental conditions,--the suiting of the hereditary primary
constituents to fresh circumstances" (p. 16).... "But as the primary
variations in the phyletic metamorphosis occurred little by little, the
secondary adaptations would probably as a rule be able to keep pace with
them. Time would thus be gained till, in the course of generations, by
constant selection of those germs the primary constituents of which are
best suited to one another, the greatest possible degree of harmony may
be reached, and consequently a definitive metamorphosis of the species
involving all the parts of the individual may occur" (p. 19).
The connecting sentences, along with those which precede and succeed, would
not, if quoted, give to the reader clearer conceptions than these by
themselves give. But when disentangled from Professor Weismann's involved
statements, the essential issues are, I think, clear enough. In the case of
the stag, that daily working together of the numerous nerves, muscles, and
bones concerned, by which they are adjusted to the carrying and using of
somewhat heavier horns, produces on them effects which, as I hold, are
inheritable, but which, as Professor Weismann holds, are not inheritable.
If they are not inheritable, what must happen? A fawn of the next
generation is born with no such adjustment of nerves, muscles and bones as
had been produced by greater exercise in the parent, and with no tendency
to such adjustment. Consequently if, in successive generations, the horns
go on enlarging, all these nerves, muscles, and bones, remaining of the
original sizes, become utterly inadequate. The result is loss of life: the
process of adaptation fails. "No," says Professor Weismann, "we must
conclude that the germ-plasm has varied in the needful manner." How so? The
process of "intra-individual selection," as he calls it, can have had no
effect, since the cells of the soma cannot influence the reproductive
cells. In what way, then, has the germ-plasm gained the characters required
for producing simultaneously all these modified co-operative parts. Well,
Professor Weismann tells us merely that we must suppose that the germ-plasm
acquires a certain sensitiveness such as gives it a proclivity to
development in the requisite ways. How is such proclivity obtainable? Only
by having a multitude of its "determinants" simultaneously changed in fit
modes. Emphasizing the fact that even a small failure in any one of the
co-operative parts may be fatal, as the sprain of an over-taxed muscle
shows us, I alleged that the chances are infinity to one against the
needful variations taking place at the same time. Divested of its
elaboration, its abstract words and technical phrases, the outcome of
Professor Weismann's explanation is that he accepts this, and asserts that
the infinitely improbable thing takes place!
Either his argument is a disguised admission of the inheritableness of
acquired characters (the effects of "intra-selection") or else it is, as
before, the assumption of a fortuitous concourse of favourable variations
in the determinants--"a fortuitous concourse of atoms."
* * * * *
Leaving here this main issue, I return now to that collateral issue named
on a preceding page as being postponed--whether the neuters among social
insects result from specially modified germ-plasms or whether they result
from the treatment received during their larval stages.
For the substantiation of his doctrine Professor Weismann is obliged to
adopt the first of these alternatives; and in his Romanes Lecture he found
it needful to deal with the evidence I brought in support of the second
alternative. He says that "poor feeding is not the _causa efficiens_ of
sterility among bees, but is merely the stimulus which _not only results in
the formation of rudimentary ovaries, but at the same time calls forth all
the other distinctive characters of the workers_" (pp. 29-30); and he says
this although he has in preceding lines admitted that it is "true of all
animals that they reproduce only feebly or not at all when badly and
insufficiently nourished:" a known cause being thus displaced by a supposed
cause. But Professor Weismann proceeds to justify his interpretation by
experimentally-obtained evidence.
He "reared large numbers of the eggs of a female blow-fly"; the larvæ of
some he fed abundantly, but the larvæ of others sparingly; and eventually
he obtained, from the one set flies of full size, and from the other small
flies. Nevertheless the small flies were fertile, as well as the others.
Here, then, was proof that innutrition had not produced infertility; and he
contends that therefore among the neuter social insects, infertility has
not resulted from innutrition. The argument seems strong, and to many will
appear conclusive; but there are two differences which entirely vitiate the
comparison Professor Weismann institutes.
One of them has been pointed out by Mr. Cunningham. In the case of the
blow-fly the food supplied to the larvæ though different in quantity was
the same in quality; in the case of the social insects the food supplied,
whether or not different in quantity, differs in quality. Among bees,
wasps, ants, &c., the larvæ of the reproductive forms are fed upon a more
nitrogenous food than are the larvæ of the workers; whereas the two sets of
larvæ of the blow-fly, as fed by Professor Weismann, were alike supplied
with highly nitrogenous food. Hence there did not exist the same cause for
non-development of the reproductive organs. Here, then, is one vitiation of
the supposed parallel. There is a second.
While the development of an embryo follows in a rude way the phyletic
metamorphoses passed through by its ancestry, the order of development of
organs is often gradually modified by the needs of particular species: the
structures being developed in such order as conduces to self-sustentation
and the welfare of offspring. Among other results there arise differences
in the relative dates of maturity of the reproductive system and of the
other systems. It is clear, _à priori_, that it must be fatal to a species
if offspring are habitually produced before the conditions requisite for
their survival are fulfilled. And hence, if the life is a complex one, and
the care taken of offspring is great, reproduction must be much longer
delayed than where the life is simple and the care of offspring absent or
easy. The contrast between men and oxen sufficiently illustrates this
truth. Now the subordination of the order of development of parts to the
needs of the species, is conspicuously shown in the contrast between these
two kinds of insects which Professor Weismann compares as though their
requirements were similar. What happens with the blow fly? If it is able to
suck up some nutriment, to fly tolerably, and to scent out dead flesh,
various of its minor organs may be more or less imperfect without
appreciable detriment to the species: the eggs can be laid in a fit place,
and that is all that is wanted. Hence it profits the species to have the
reproductive system developed comparatively early--in advance, even, of
various less essential parts. Quite otherwise is it with social insects,
which take such remarkable care of their young; or rather to make the case
parallel--quite otherwise is it with those types from which the social
insects have descended, bringing into the social state their inherited
instincts and constitutions. Consider the doings of the mason-wasp, or
mason-bee, or those of the carpenter-bee. What, in these cases, must the
female do that she may rear members of the next generation? There is a fit
place for building or burrowing to be chosen; there is the collecting
together of grains of sand and cementing them into a strong and water-proof
cell, or there is the burrowing into wood and there building several cells;
there is the collecting of food to place along with the eggs deposited in
these cells, solitary or associated, including that intelligent choice of
small caterpillars which, discovered and carried home, are carefully packed
away and hypnotized by a sting, so that they may live until the growing
larva has need of them. For all these proceedings there have to be provided
the fit external organs--cutting instruments, &c., and the fit internal
organs--complicated nerve-centres in which are located these various
remarkable instincts, and ganglia by which these delicate operations have
to be guided. And these special structures have, some if not all of them,
to be made perfect and brought into efficient action before egg-laying
takes place. Ask what would happen if the reproductive system were active
in advance of these ancillary appliances. The eggs would have to be laid
without protection or food, and the species would forthwith disappear. And
if that full development of the reproductive organs which is marked by
their activity, is not needful until these ancillary organs have come into
play, the implication, in conformity with the general law above indicated,
is that the perfect development of the reproductive organs will take place
later than that of these ancillary organs, and that if innutrition checks
the general development, the reproductive organs will be those which
chiefly suffer. Hence, in the social types which have descended from these
solitary types, this order of evolution of parts will be inherited, and
will entail the results I have inferred.
If only deductively reached, this conclusion would, I think, be fully
justified. But now observe that it is more than deductively reached. It is
established by observation. Professor Riley, Ph.D., late Government
Entomologist of the United States, in his annual address as President of
the Biological Society of Washington,[134] on January 29, 1894, said:--
"Among the more curious facts connected with these Termites, because of
their exceptional nature, is the late development of the internal sexual
organs in the reproductive forms." (p. 34.)
Though what has been shown of the Termites has not been shown of the other
social insects, which belong to a different order, yet, considering the
analogies between their social states and between their constitutional
requirements, it is a fair inference that what holds in the one case holds
partially, if not fully, in the other. Should it be said that the larval
forms do not pass into the pupa state in the one case as they do in the
other, the answer is that this does not affect the principle. The larva
carries into the pupa state a fixed quantity of tissue-forming material for
the production of the imago. If the material is sufficient, then a complete
imago is formed. If it is not sufficient, then, while the earlier formed
organs are not affected by the deficiency, the deficiency is felt when the
latest formed organs come to be developed, and they are consequently
imperfect.
Even if left without reply, Professor Weismann's interpretation commits him
to some insuperable difficulties, which I must now point out.
Unquestionably he has "the courage of his opinions;" and it is shown
throughout this collateral discussion as elsewhere. He is compelled by
accumulated evidence to admit "that there is only _one_ kind of egg from
which queens and workers as well as males arise."[135] But if the
production of one or other form from the same germ does not result from
speciality of feeding, what does it result from? Here is his reply:--
"We must rather suppose that the primary constituents of two distinct
reproductive systems--_e. g._ those of the queen and worker--are
contained in the germ-plasm of the egg."[136]
"The courage of his opinions," which Professor Weismann shows in this
assumption, is, however, quite insufficient. For since he himself has just
admitted that there is only one kind of egg for queens, workers, and males,
he must at any rate assume three sets of "determinants." (I find that on a
subsequent page he does so.) But this is not enough, for there are, in many
cases, two if not more kinds of workers, which implies that four sets of
determinants must co-exist in the same egg. Even now we have not got to the
extent of the assumption required. In the address above referred to on
"Social Insects from Psychical and Evolutional Points of View," Professor
Riley gives us (p. 33) the--
_Forms in a Termes Colony under Normal Conditions._
1. Youngest larvæ.
/ \
/ \
/ \
2. Larvæ [of those] unfit 3. Larvæ [that will be] fit
for reproduction. for reproduction.
/ \ / \
/ \ / \
4. Larvæ of 5. Larvæ of 8. Nymphs of 9. Nymphs of 2nd
workers. soldiers. 1st form. form.
| | |
6. Workers. 7. Soldiers. 10. Winged forms.
|
11. True royal pairs.
Hence as, in this family tree, the royal pair includes male and female, it
results that there are _five_ different adult forms (Grassi says there are
two others) arising from like eggs or larvæ; and Professor Weismann's
hypothesis becomes proportionately complicated. Let us observe what the
complications are.
It often happens in controversy--metaphysical controversy more than any
other--that propositions are accepted without their terms having been
mentally represented. In public proceedings documents are often "taken as
read," sometimes with mischievous results; and in discussions propositions
are often taken as thought when they have not been thought and cannot be
thought. It sufficiently taxes imagination to assume, as Professor Weismann
does, that two sets of "ids" or of "determinants" in the same egg are,
throughout all the cell-divisions which end in the formation of the
_morula_, kept separate, so that they may subsequently energize
independently; or that if they are not thus kept separate, they have the
power of segregating in the required ways. But what are we to say when
three, four, and even five sets of "ids" or bundles of "determinants" are
present? How is dichotomous division to keep these sets distinct; or if
they are not kept distinct, what shall we say to the chaos which must arise
after many fissions, when each set in conflict with the others strives to
produce its particular structure? And how are the conquering determinants
to find they ways out of the _mêlée_ to the places where they are to fulfil
their organizing functions? Even were they all intelligent beings and each
had a map by which to guide his movements, the problem would be
sufficiently puzzling. Can we assume it to be solved by unconscious units?
Thus even had Professor Weismann shown that the special structures of the
different individuals in an insect-community are not due to differences in
the nurtures they receive, which he has failed to do, he would still be met
by this difficulty in the way of his own view, in addition to the three
other insuperable difficulties grouped together in a preceding section.
* * * * *
The collateral issue, which has occupied the largest space in the
controversy, has, as commonly happens, begotten a second generation of
collateral issues. Some of these are embodied in the form of questions put
to me, which I must here answer, lest it should be supposed that they are
unanswerable and my view therefore untenable.
In the notes he appends to his Romanes Lecture, Professor Weismann
writes:--
"One of the questions put to Spencer by Ball is quite sufficient to show
the utter weakness of the position of Lamarckism:--if their
characteristics did not arise among the workers themselves, but were
transmitted from the pre-social time, how does it happen that the queens
and drones of every generation can give anew to the workers the
characteristics which they themselves have long ago lost?" (p. 68).
It is curious to see put forward in so triumphant a manner, by a professed
naturalist, a question so easily disposed of. I answer it by putting
another. How does it happen that among those moths of which the female has
but rudimentary wings, she continues to endow the males of her species with
wings? How does it happen, for example, that among the _Geometridæ_, the
peculiar structures and habits of which show that they have all descended
from a common ancestor, some species have winged females and some wingless
females; and that though they have lost the wings the ancestral females
had, these wingless females convey to the males the normal developments of
wings? Or, still better, how is it that in the _Psychidæ_ there are
apterous worm-like females, which lay eggs that bring forth winged males of
the ordinary imago form? If for males we read workers, the case is parallel
to the cases of those social insects, the queens of which bequeath
characteristics they have themselves lost. The ordinary facts of embryonic
evolution yield us analogies. What is the most common trait in the
development of the sexes? When the sexual organs of either become
pronounced, the incipient ancillary organs belonging to the opposite sex
cease to develop and remain rudiments, while the organs special to the sex,
essential and nonessential, become fully developed. What, then, must happen
with the queen-ant, which, through countless generations, has ceased to use
certain structures and has lost them from disuse? If one of the eggs which
she lays, capable, as Professor Weismann admits, of becoming queen, male,
or worker of one or other kind, does not at a certain stage begin actively
to develop its reproductive system, then those organs of the ancestral or
pre-social type which the queen has lost begin to develop, and a worker
results.
Another difficulty in the way of my view, supposed to be fatal, is that
presented by the Honey-ants--aberrant members of certain ant-colonies which
develop so enormously the pouch into which the food is drawn, that the
abdomen becomes little else than a great bladder out of which the head,
thorax, and legs protrude. This, it is thought, cannot be accounted for
otherwise than as a consequence of specially endowed eggs, which it has
become profitable to the community for the queen to produce. But the
explanation fits in quite easily with the view I have set forth. No one
will deny that the taking in of food is the deepest of vital requirements,
and the correlative instinct a dominant one; nor will any one deny that the
instinct of feeding young is less deeply seated--comes later in order of
time. So, too, every one will admit that the worker-bee or worker-ant
before regurgitating food into the mouth of a larva must first of all take
it in. Hence, alike in order of time and necessity, it is to be assumed
that development of the nervous structures which guide self-nutrition,
precedes development of the nervous structures which guide the feeding of
larvæ. What, then, will in some cases happen, supposing there is an
arrested development consequent on innutrition? It will in some cases
happen that while the nervous centres prompting and regulating deglutition
are fully formed, the formation of those prompting and regulating the
regurgitation of the food into the mouths of larvæ are arrested. What will
be the consequence? The life of the worker is mainly passed in taking in
food and putting it out again. If the putting out is stopped its life will
be mainly passed in taking in food. The receptacle will go on enlarging and
it will eventually assume the monstrous form that we see.[137]
Here, however, to exclude misinterpretations, let me explain. I by no means
deny that variation and selection have produced, in these
insect-communities, certain effects such as Mr. Darwin suggested. Doubtless
ant-queens vary; doubtless there are variations in their eggs; doubtless
differences of structure in the resulting progeny sometimes prove
advantageous to the stirp, and originate slight modifications of the
species. But such changes, legitimately to be assumed, are changes in
single parts--in single organs or portions of organs. Admission of this
does not involve admission that there can take place numerous correlated
variations in different and often remote parts, which must take place
simultaneously or else be useless. Assumption of this is what Professor
Weismann's argument requires, and assumption of this we have seen to be
absurd.
Before leaving the general problem presented by the social insects, let me
remark that the various complexities of action not explained by inheritance
from pre-social or semi-social types, are probably due to accumulated and
transmitted knowledge. I recently read an account of the education of a
butterfly, carried to the extent that it became quite friendly with its
protector and would come to be fed. If a non-social and relatively
unintelligent insect is capable of thus far consciously adjusting its
actions, then it seems a reasonable supposition that in a community of
social insects there has arisen a mass of experience and usage into which
each new individual is initiated; just as happens among ourselves. We have
only to consider the chaos which would result were we suddenly bereft of
language, and if the young were left to grow up without precept and
example, to see that very probably the polity of an insect community is
made possible by the addition of intelligence to instinct, and the
transmission of information through sign-language.
* * * * *
There remains now the question of _panmixia_, which stands exactly where it
did when I published the "Rejoinder to Professor Weismann."
After showing that the interpretation I put upon his view was justified by
certain passages quoted; and after pointing out that one of his adherents
had set forth the view which I combated--if not as his view yet as
supplementary to it; I went on to criticize the view as set forth afresh by
Professor Weismann himself. I showed that as thus set forth the actuality
of the supposed cause of decrease in disused organs, implies that _minus_
variations habitually exceed _plus_ variations--in degree or in number, or
in both. Unless it can be proved that such an excess ordinarily occurs, the
hypothesis of _panmixia_ has no place; and I asked, where is the proof that
it occurs.
No reply.
Not content with this abstract form of the question I put it also in a
concrete form, and granted for the nonce Professor Weismann's assumption:
taking the case of the rudimentary hind limbs of the whale. I said that
though, during those early stages of decrease in which the disused limbs
were external, natural selection probably had a share in decreasing them,
since they were then impediments to locomotion, yet when they became
internal, and especially when they had dwindled to nothing but remnants of
the femurs, it is impossible to suppose that natural selection played any
part: no whale could have survived and initiated a more prosperous stirp in
virtue of the economy achieved by such a decrease. The operation of natural
selection being out of the question, I inquired whether such a decrease,
say of one-half when the femurs weighed a few ounces, occurring in one
individual, could be supposed in the ordinary course of reproduction to
affect the whole of the whale species inhabiting the Arctic Seas and the
North Atlantic Ocean; and so on with successive diminutions until the
rudiments had reached their present minuteness. I asked whether such an
interpretation could be rationally entertained.
No reply.
Now in the absence of replies to these two questions it seems to me that
the verdict must go against Professor Weismann by default. If he has to
surrender the hypothesis of _panmixia_, what results? All that evidence
collected by Mr. Darwin and others, regarded by them as proof of the
inheritance of acquired characters, which was cavalierly set aside on the
strength of this alleged process of panmixia, is reinstated. And this
reinstated evidence, joined with much evidence since furnished, suffices to
establish the repudiated interpretation.
In the printed report of his Romanes Lecture, after fifty pages of
complicated speculations which we are expected to accept as proofs,
Professor Weismann ends by saying, in reference to the case of the neuter
insects:--
"This case is of additional interest, as it may serve to convince those
naturalists who are still inclined to maintain that acquired characters
are inherited, and to support the Lamarckian principle of development,
that their view cannot be the right one. It has not proved tenable in a
single instance" (p. 54).
Most readers of the foregoing pages will think that since Professor
Weismann has left one after another of my chief theses without reply, this
is rather a strong assertion; and they will still further raise their
eyebrows on remembering that, as I have shown, where he has given answers
his answers are invalid.
* * * * *
And now we come to the additions which I indicated at the outset as having
to be made--certain evidences which have come to light since this
controversy commenced.
When, by a remembered observation made in boyhood, joined with the familiar
fact that worker-larvæ can be changed into the larvæ of queens by feeding,
I was led to suggest that probably all the variations of form in the social
insects are consequent on differences of nurture, I was unaware that
observations and experiments were being made which have justified this
suggestion. Professor Grassi has recently published accounts of the
food-habits of two European species of Termites, shewing that the various
forms are due to feeding. He is known to be a most careful observer, and
some of the most curious of his facts are confirmed by the collection of
white ants exhibited by Dr. David Sharp, F.R.S., at the _soirée_ of the
Royal Society in May last. He has favoured me with the following account of
Grassi's results, which I publish with his assent:--
"There is great variety as to the constituents of the community and
economy of the species in White Ants. One of the simplest conditions
known is that studied by Grassi in the case of the European species
Calotermes flavicollis. In this species there is no worker caste; the
adult forms are only of two kinds, viz., soldiers, and the males and
females; the sexes are externally almost indistinguishable, and there are
males and females of soldiers as well as of the winged forms, though the
sexual organs do not undergo their full development in any soldier
whether male or female.
"The soldier is not however a mere instance of simple arrested
development. It is true that there is in it arrested development of the
sexual organs, but this is accompanied by change of form of other
parts--changes so extreme that one would hardly suppose the soldier to
have any connection with either the young or the adult of the winged
forms.
"Now according to Grassi the whole of the individuals when born are
undifferentiated forms (except as to sex), and each one is capable of
going on the natural course of development and thus becoming a winged
insect, or can be deviated from this course and made into a soldier; this
is accomplished by the White Ants by special courses of feeding.
"The evidence given by Grassi is not conclusive as to the young being all
born alike; and it may be that there are some individuals born that could
not be deviated from the natural course and made into soldiers. But there
is one case which seems to show positively that the deviation Grassi
believes to occur is real, and not due to the selection by the ants of an
individual that though appearing to our eyes undifferentiated is not
really so. This is that an individual can be made into a soldier after it
has visibly undergone one half or more of the development into a winged
form. The Termites can in fact operate on an individual that has already
acquired the rudiments of wings and whose head is totally destitute of
any appearance of the shape of the armature peculiar to the soldier, and
can turn it into a soldier; the rudiments of the wings being in such a
case nearly entirely re-absorbed."
Grassi has been for many years engaged in investigating these phenomena,
and there is no reason for rejecting his statement. We can scarcely avoid
accepting it, and if so, Professor Weismann's hypothesis is conclusively
disposed of. Were there different sets of "determinants" for the
soldier-form and for the winged sexual form, those "determinants" which had
gone a long way towards producing the winged sexual form, would inevitably
go on to complete that form, and could not have their proclivity changed by
feeding.
[Yet more evidence to the like effect has since become known. At the
meeting of the Entomological Society, on March 14, 1894 (reported in
_Nature_, March 29):--
"Dr. D. Sharp, F.R.S., exhibited a collection of white ants (_Termites_),
formed by Mr. G. D. Haviland in Singapore, which comprised about twelve
species, of most of which the various forms were obtained. He said that
Prof. Grassi had recently made observations on the European species, and
had brought to light some important particulars; and also that in the
discussion that had recently been carried on between Mr. Herbert Spencer
and Prof. Weismann, the former had stated that in his opinion the
different forms of social insects were produced by nutrition. Prof.
Grassi's observations showed this view to be correct, and the specimens
now exhibited confirmed one of the most important points in his
observations. Dr. Sharp also stated that Mr. Haviland found in one nest
eleven neoteinic queens--that is to say, individuals having the
appearance of the queen in some respects, while in others they are still
immature."
Another similarly conclusive verification I published in _Nature_ for
December 6, 1894, under the title "The Origin of Classes among the
'Parasol' Ants." The letter ran as follows:--
"Mr. J. H. Hart is Superintendent of the Royal Botanic Gardens in
Trinidad. He has sent me a copy of his report presented to the
Legislative Council in March, 1893, and has drawn my attention to certain
facts contained in it concerning the 'Parasol' ants--the leaf-cutting
ants which feed on the fungi developed in masses of the cut leaves
carried to their nests. Both Mr. Bates and Mr. Belt described these ants,
but described, it seems, different, though nearly allied, species, the
habits of which are partially unlike. As they are garden-pests, Mr. Hart
was led to examine into the development and social arrangements of these
ants; establishing, to that end, artificial nests, after the manner
adopted by Sir John Lubbock. Several of the facts set down have an
important bearing on a question now under discussion. The following
extracts, in which they are named, I abridge by omitting passages not
relevant to the issue:--
"'The history of my nests is as follows: Nos. 1 and 2 were both taken
(August 9) on the same day, while destroying nests in the Gardens, and
were portions of separate nests but of the same species. No. 3 was
procured on September 5, and is evidently a different although an allied
species to Nos. 1 and 2.
"'Finding neither of my nests had a queen, I procured one from another
nest about to be destroyed, and placed it with No. 1 nest. It was
received by the workers, and at once attended by a numerous retinue in
royal style. On August 30 I removed the queen from No. 1 and placed it
with No. 2, when it was again received in a most loyal manner....
"'Ants taken from Nos. 1 and 2 and placed with No. 3 were immediately
destroyed by the latter, and even the soldiers of No. 3, as well as
workers or nurses, were destroyed when placed with Nos. 1 and 2.
"'In nest No. 2, from which I removed the queen on August 30, there are
now in the pupa stage several queens and several males. The forms of ant
in nests Nos. 1 and 2 are as follows: (_a_) queen, (_b_) male (both
winged, but the queen loses its wings after marital flight), (_c_) large
workers, (_d_) small workers, and (_e_) nurses. In nest No. 3 I have not
yet seen the queen or male, but it possesses--(_a_) soldier, (_b_) larger
workers, (_c_) smaller workers, and (_d_) nurses; but these are different
in form to those of nests No. 1 and No. 2. Probably we might add a third
form of worker, as there are several sizes in the nest....
"'It is curious that in No. 1 nest, from which the queen was removed on
August 30, new queens and males are now being developed, while in No. 2
nest, where the queen is at present, nothing but workers have been
brought out, and if a queen larva or pupa is placed there it is at once
destroyed, while worker larvæ or pupæ are amicably received. In No. 3 all
the eggs, larvæ, and pupæ collected with the nest have been hatched, and
no eggs have since made their appearance to date. There is no queen with
this nest.... On November 14 I attempted to prove by experiment how small
a number of "parasol" ants it required to form a new colony. I placed two
dozen of ants (one dozen workers and one dozen nurses) in two separate
nests, No. 4 and No. 5. With No. 4 I placed a few larvæ with a few rose
petals for them to manipulate. With No. 5 I gave a small piece of nest
covered with mycelium. On the 16th these nests were destroyed by small
foraging ants, known as the "sugar" or "meat" ant, and I had to remove
them and replace with a new colony. My notes on these are not
sufficiently lengthy to be of much importance. But I noted four eggs laid
on the 16th, or two days after being placed in their new quarters; no
queen being present. The experiment is being continued. I may mention
that in No. 4 nest, in which no fungus was present, the larvæ of all
sizes appeared to change into the pupæ stage at once for want of food [a
fact corresponding with the fact I have named as observed by myself sixty
years ago in the case of wasp larvæ]. The circumstance tends to show that
the development of the insect is influenced entirely by the feeding it
gets in the larva stage.
"'In nest No. 2 before the introduction of a queen there were no eggs or
larvæ. The first worker was hatched on October 27, or fifty-seven days
afterwards, and a continual succession has since been maintained, but as
yet (November 19) no males or queens have made their appearance.'
"In a letter accompanying the report, Mr. Hart says:--
"'Since these were published, my notes go to prove that ants can
practically manufacture at will, male, female, soldier, worker, or nurse.
Some of the workers are capable of laying eggs, and from these can be
produced all the various forms as well as from a queen's egg.
"'There does not, however, appear to be any difference in the character
of the food; as I cannot find that the larger larvæ are fed with anything
different to that given to the smaller.'
"These results were obtained before the recent discussion of the question
commenced, and joined with the other evidence entirely dispose of those
arguments which Prof. Weismann bases on facts furnished by the social
insects."]
The other piece of additional evidence I have referred to, is furnished by
two papers contributed to _The Journal of Anatomy and Physiology_ for
October 1893 and April 1894, by R. Havelock Charles, M. D., &c. &c.,
Professor of Anatomy in the Medical College, Lahore. These papers set forth
the differences between the leg-bones of Europeans and those of the Punjaub
people--differences caused by their respective habits of sitting in chairs
and squatting on the ground. He enumerates more than twenty such
differences, chiefly in the structures of the knee-joint and ankle-joint.
From the _résumé_ of his second paper I quote the following passages, which
sufficiently show the data and the inferences:--
"7. The habits as to sitting postures of Europeans differ from those of
their prehistoric ancestors, the Cave-dwellers, &c., who probably
squatted on the ground.
"8. The sitting postures of Orientals are the same now as ever. They have
retained the habits of their ancestors. The Europeans have not done so.
"9. Want of use would induce changes in form and size, and so, gradually,
small differences would be integrated till there would be total
disappearance of the markings on the European skeleton, as no advantage
would accrue to him from the possession of facets on his bones fitting
them for postures not practised by him.
"10. The facets seen on the bones of the Panjabi infant or foetus have
been transmitted to it by the accumulation of peculiarities gained by
habit in the evolution of its racial type--in which an acquisition having
become a permanent possession, 'profitable to the individual under its
conditions of life,' is transmitted as a useful inheritance.
"11. These markings are due to the influence of certain positions, which
are brought about by the use of groups of muscles, and they are the
definite results produced by actions of these muscles.
"12. The effects of the use of the muscles mentioned in No. 11 are
transmitted to the offspring, for the markings are present in the
_foetus-in-utero_, in the child at birth, and in the infant.
"13. The markings are instances of the transmission of acquired
characters, which heritage in the individual, function subsequently
develops."
No other conclusion appears to me possible. _Panmixia_, even were it not
invalidated by its unwarranted assumption as above shown, would be out of
court: the case is not a case of either increase or decrease of size but of
numerous changes of form. Simultaneous variation of co-operative parts
cannot be alleged, since these co-operative parts have not changed in one
way but in various ways and degrees. And even were it permissible to
suppose that the required different variations had taken place
simultaneously, natural selection cannot be supposed to have operated. The
assumption would imply that in the struggle for existence, individuals of
the European races who were less capable than others of crouching and
squatting, gained by those minute changes of structure which incapacitated
them, such advantages that their stirps prevailed over other stirps--an
absurd supposition.
And now I must once more point out that a grave responsibility rests on
biologists in respect of the general question; since wrong answers lead,
among other effects, to wrong beliefs about social affairs and to
disastrous social actions. In me this conviction has unceasingly
strengthened. Though _The Origin of Species_ proved to me that the
transmission of acquired characters cannot be the sole factor in organic
evolution, as I had assumed in _Social Statics_ and in _The Principles of
Biology_, published in pre-Darwinian days, yet I have never wavered in the
belief that it is a factor and an all-important factor. And I have felt
more and more that since all the higher sciences are dependent on the
science of life, and must have their conclusions vitiated if a fundamental
datum given to them by the teachers of this science is erroneous, it
behoves these teachers not to let an erroneous datum pass current: they are
called on to settle this vexed question one way or other. The times give
proof. The work of Mr. Benjamin Kidd on _Social Evolution_, which has been
so much lauded, takes Weismannism as one of its data; and if Weismannism be
untrue, the conclusions Mr. Kidd draws must be in large measure erroneous
and may prove mischievous.
POSTSCRIPT.--Since the foregoing pages have been put in type there has
appeared in _Natural Science_ for September, an abstract of certain parts
of a pamphlet by Professor Oscar Hertwig, setting forth facts directly
bearing on Professor Weismann's doctrine respecting the distinction between
reproductive cells and somatic cells. In _The Principles of Biology_, § 77,
I contended that reproductive cells differ from other cells composing the
organism, only in being unspecialized. And in support of the hypothesis
that tissue-cells in general have a reproductive potentiality, I instanced
the cases of the _Begonia phyllomaniaca_ and _Malaxis paludosa_. In the
thirty years which have since elapsed, many facts of like significance have
been brought to light, and various of these are given by Professor Hertwig.
Here are some of them:--
"Galls are produced under the stimulus of the insect almost anywhere on
the surface of a plant. Yet in most cases these galls, in a sense grown
at random on the surface of a plant, when placed in damp earth will give
rise to a young plant. In the hydroid _Tubularia mesembryanthemum_, when
the polyp heads are cut off, new heads arise. But if both head and root
be cut off, and the upper end be inserted in the mud, then from the
original upper end not head-polyps but root filaments will arise, while
from the original lower end not root filaments but head-polyps will
grow.... Driesch, by separating the first two and the first four
segmentation spheres of an _Echinus_ ovum, obtained two or four normal
plutei, respectively one half and a quarter of the normal size.... So,
also, in the case of _Amphioxus_, Wilson obtained a normal, but
proportionately diminished embryo with complete nervous system from a
separated sphere of a two- or four- or eight celled stage.... Chabry
obtained normal embryos in cases where some of the segmentation-spheres
had been artificially destroyed."
These evidences, furnished by independent observers, unite in showing,
firstly, that all the multiplying cells of the developing embryo are alike;
and, secondly, that the soma-cells of the adult severally retain, in a
latent form, all the powers of the original embryo-cell. If these facts do
not disprove absolutely Professor Weismann's hypothesis, we may wonderingly
ask what facts would disprove it?
Since Hertwig holds that all the cells forming an organism of any species
primarily consist of the same components, I at first thought that his
hypothesis was identical with my own hypothesis of "physiological units,"
or, as I would now call them, constitutional units. It seems otherwise,
however; for he thinks that each cell contains "only those material
particles which are bearers of cell-properties," and that organs "are the
functions of cell-complexes." To this it may be replied that the ability to
form the appropriate cell-complexes, itself depends upon the constitutional
units contained in the cells.
APPENDIX C.
THE INHERITANCE OF FUNCTIONALLY-WROUGHT MODIFICATIONS: A SUMMARY.
The assertion that changes of structure caused by changes of function are
transmitted to descendants is continually met by the question--Where is the
evidence? When some facts are assigned in proof, they are pooh-poohed as
insufficient. If after a time the question is raised afresh and other facts
are named, there is a like supercilious treatment of them. Successively
rejected in this way, the evidences do not accumulate in the minds of
opponents; and hence produce little or no effect. When they are brought
together, however, it turns out that they are numerous and weighty. We will
group them into negative and positive.
* * * * *
Negative evidence is furnished by those cases in which traits otherwise
inexplicable are explained if the structural effects of use and disuse are
transmitted. In the foregoing chapters and appendices three have been
given.
(1) Co-adaptation of co-operative parts comes first. This has been
exemplified by the case of enlarged horns in a stag, by the case of an
animal led into the habit of leaping, and in the case of the giraffe (cited
in "The Factors of Organic Evolution"); and it has been shown that the
implied co-adaptations of parts cannot possibly have been effected by
natural selection.
(2) The possession of unlike powers of discrimination by different parts of
the human skin, was named as a problem to be solved on the hypothesis of
natural selection or the hypothesis of panmixia; and it was shown that
neither of these can by any twisting yield a solution. But the facts
harmonize with the hypothesis that the effects of use are inherited.
(3) Then come the cases of those rudimentary organs which, like the hind
limbs of the whale, have nearly disappeared. Dwindling by natural selection
is here out of the question; and dwindling by panmixia, even were its
assumptions valid, would be incredible. But as a sequence of disuse the
change is clearly explained.
Failure to solve any _one_ of these three problems would, I think, alone
prove the Neo-Darwinian doctrines untenable; and the fact that we have
_three_ unsolved problems seems to me fatal.
* * * * *
From this negative evidence, turn now to the positive evidence. This falls
into several groups.