purely hypothetical, and that other suppositions have an equal right to
consideration.
For example, is it not possible that, at the prodigious temperature
which would seem to exist at 100 miles below the surface, all the
metallic bases may behave as mercury does at a red heat, when it refuses
to combine with oxygen; while, nearer the surface, and therefore at a
lower temperature, they may enter into combination (as mercury does with
oxygen a few degrees below its boiling-point) and so give rise to a
heat totally distinct from that which they possess as cooling bodies?
And has it not also been proved by recent researches that the quality of
the atmosphere may immensely affect its permeability to heat; and,
consequently, profoundly modify the rate of cooling the globe as a
whole?
I do not think it can be denied that such conditions may exist, and may
so greatly affect the supply, and the loss, of terrestrial heat as to
destroy the value of any calculations which leave them out of sight.
My functions as your advocate are at an end. I speak with more than the
sincerity of a mere advocate when I express the belief that the case
against us has entirely broken down. The cry for reform which has been
raised without, is superfluous, inasmuch as we have long been reforming
from within, with all needful speed. And the critical examination of the
grounds upon which the very grave charge of opposition to the principles
of Natural Philosophy has been brought against us, rather shows that we
have exercised a wise discrimination in declining, for the present, to
meddle with our foundations.
FOOTNOTES:
[39] On Geological Time. By Sir W. Thomson, LL.D. Transactions of the
Geological Society of Glasgow, vol. iii.
[40] The Theory of the Earth, vol. i. p. 173, note.
[41] Ibid. p. 281.
[42] Ibid. p. 371.
[43] The Theory of the Earth, vol. i. p. 200.
[44] The Theory of the Earth, vol. i. pp. 16, 17.
[45] The Theory of the Earth, vol. i. p. 223.
[46] Principles of Geology, vol. ii. p. 211.
[47] Principles of Geology, vol. ii. p. 613.
[48] "Man darf es sich also nicht befremden lassen, wenn ich mich
unterstehe zu sagen, dass eher die Bildung aller Himmelskörper, die
Ursache ihrer Bewegungen, kurz der Ursprung der ganzen gegenwärtigen
Verfassung des Weltbaues werden können eingesehen werden, ehe die
Erzeugung eines einzigen Krautes oder einer Raupe aus mechanischen
Gründen, deutlich und vollständig kund werden wird."--KANT'S _Sämmtliche
Werke_, Bd. I. p. 220.
[49] Grant ("History of Physical Astronomy," p. 574) makes but the
briefest reference to Kant.
[50] "Allgemeine Naturgeschichte und Theorie des Himmels; oder Versuch
von der Verfassung und dem mechanischen Ursprunge des ganzen
Weltgebäudes nach Newton'schen Grundsatzen abgehandelt."--KANT'S
_Sämmtliche Werke_, Bd. i. p. 207.
[51] Système du Monde, tome ii. chap. 6
[52] Kant's "Sämmtliche Werke," Bd. viii. p. 145.
[53] Sir William Thomson implies (loc. cit. p. 16), that the precise
time is of no consequence: "the principle is the same;" but, as the
principle is admitted, the whole discussion turns on its practical
results.
[54] "Untersuchung der Frage ob die Erde in ihrer Umdrehung um die
Achse, wodurch sie die Abwechselung des Tages und der Nacht
hervorbringt, einige Veränderung seit den ersten Zeiten ihres Ursprunges
erlitten habe, &c."--KANT'S _Sämmtliche Werke_, Bd. i. p. 178.
[55] Sir W. Thomson, loc. cit., p. 14.
[56] Loc. cit., p. 27
[57] Ibid.
[58] It will be understood that I do not wish to deny that the earth's
rotation _may be_ undergoing retardation.
[59] Loc. cit., p. 20.
[60] Loc. cit., p. 24.
XII.
THE ORIGIN OF SPECIES.
Mr. Darwin's long-standing and well-earned scientific eminence probably
renders him indifferent to that social notoriety which passes by the
name of success; but if the calm spirit of the philosopher have not yet
wholly superseded the ambition and the vanity of the carnal man within
him, he must be well satisfied with the results of his venture in
publishing the "Origin of Species." Overflowing the narrow bounds of
purely scientific circles, the "species question" divides with Italy and
the Volunteers the attention of general society. Everybody has read Mr.
Darwin's book, or, at least, has given an opinion upon its merits or
demerits; pietists, whether lay or ecclesiastic, decry it with the mild
railing which sounds so charitable; bigots denounce it with ignorant
invective; old ladies, of both sexes, consider it a decidedly dangerous
book, and even savans, who have no better mud to throw, quote antiquated
writers to show that its author is no better than an ape himself; while
every philosophical thinker hails it as a veritable Whitworth gun in the
armory of liberalism; and all competent naturalists and physiologists,
whatever their opinions as to the ultimate fate of the doctrines put
forth, acknowledge that the work in which they are embodied is a solid
contribution to knowledge and inaugurates a new epoch in natural
history.
Nor has the discussion of the subject been restrained within the limits
of conversation. When the public is eager and interested, reviewers must
minister to its wants; and the genuine _littérateur_ is too much in the
habit of acquiring his knowledge from the book he judges--as the
Abyssinian is said to provide himself with steaks from the ox which
carries him--to be withheld from criticism of a profound scientific work
by the mere want of the requisite preliminary scientific acquirement;
while, on the other hand, the men of science who wish well to the new
views, no less than those who dispute their validity, have naturally
sought opportunities of expressing their opinions. Hence it is not
surprising that almost all the critical journals have noticed Mr.
Darwin's work at greater or less length; and so many disquisitions, of
every degree of excellence, from the poor product of ignorance, too
often stimulated by prejudice, to the fair and thoughtful essay of the
candid student of Nature, have appeared, that it seems an almost
hopeless task to attempt to say anything new upon the question.
But it may be doubted if the knowledge and acumen of prejudged
scientific opponents, or the subtlety of orthodox special pleaders, have
yet exerted their full force in mystifying the real issues of the great
controversy which has been set afoot, and whose end is hardly likely to
be seen by this generation; so that, at this eleventh hour, and even
failing anything new, it may be useful to state afresh that which is
true, and to put the fundamental positions advocated by Mr. Darwin in
such a form that they may be grasped by those whose special studies lie
in other directions. And the adoption of this course may be the more
advisable, because notwithstanding its great deserts, and indeed partly
on account of them, the "Origin of Species" is by no means an easy book
to read--if by reading is implied the full comprehension of an author's
meaning.
We do not speak jestingly in saying that it is Mr. Darwin's misfortune
to know more about the question he has taken up than any man living.
Personally and practically exercised in zoology, in minute anatomy, in
geology; a student of geographical distribution, not on maps and in
museums only, but by long voyages and laborious collection; having
largely advanced each of these branches of science, and having spent
many years in gathering and sifting materials for his present work, the
store of accurately registered facts upon which the author of the
"Origin of Species" is able to draw at will is prodigious.
But this very superabundance of matter must have been embarrassing to a
writer who, for the present, can only put forward an abstract of his
views; and thence it arises, perhaps, that notwithstanding the clearness
of the style, those who attempt fairly to digest the book find much of
it a sort of intellectual pemmican--a mass of facts crushed and pounded
into shape, rather than held together by the ordinary medium of an
obvious logical bond: due attention will, without doubt, discover this
bond, but it is often hard to find.
Again, from sheer want of room, much has to be taken for granted which
might readily enough be proved; and hence, while the adept, who can
supply the missing links in the evidence from his own knowledge,
discovers fresh proof of the singular thoroughness with which all
difficulties have been considered and all unjustifiable suppositions
avoided, at every reperusal of Mr. Darwin's pregnant paragraphs, the
novice in biology is apt to complain of the frequency of what he fancies
is gratuitous assumption.
Thus while it may be doubted if, for some years, any one is likely to be
competent to pronounce judgment on all the issues raised by Mr. Darwin,
there is assuredly abundant room for him, who, assuming the humbler,
though perhaps as useful, office of an interpreter between the "Origin
of Species" and the public, contents himself with endeavouring to point
out the nature of the problems which it discusses; to distinguish
between the ascertained facts and the theoretical views which it
contains; and finally, to show the extent to which the explanation it
offers satisfies the requirements of scientific logic. At any rate, it
is this office which we propose to undertake in the following pages.
It may be safely assumed that our readers have a general conception of
the nature of the objects to which the word "species" is applied; but it
has, perhaps, occurred to few, even of those who are naturalists _ex
professo_, to reflect, that, as commonly employed, the term has a double
sense and denotes two very different orders of relations. When we call a
group of animals, or of plants, a species, we may imply thereby either,
that all these animals or plants have some common peculiarity of form
or structure; or, we may mean that they possess some common functional
character. That part of biological science which deals with form and
structure is called Morphology--that which concerns itself with
function, Physiology--so that we may conveniently speak of these two
senses, or aspects, of "species"--the one as morphological, the other as
physiological. Regarded from the former point of view, a species is
nothing more than a kind of animal or plant, which is distinctly
definable from all others, by certain constant, and not merely sexual,
morphological peculiarities. Thus horses form a species, because the
group of animals to which that name is applied is distinguished from all
others in the world by the following constantly associated characters.
They have 1. A vertebral column; 2. Mammæ; 3. A placental embryo; 4.
Four legs; 5. A single well-developed toe in each foot provided with a
hoof; 6. A bushy tail; and 7. Callosities on the inner sides of both the
fore and the hind legs. The asses, again, form a distinct species,
because, with the same characters, as far as the fifth in the above
list, all asses have tufted tails, and have callosities only on the
inner side of the fore legs. If animals were discovered having the
general characters of the horse, but sometimes with callosities only on
the fore legs, and more or less tufted tails; or animals having the
general characters of the ass, but with more or less bushy tails, and
sometimes with callosities on both pairs of legs, besides being
intermediate in other respects--the two species would have to be merged
into one. They could no longer be regarded as morphologically distinct
species, for they would not be distinctly definable one from the other.
However bare and simple this definition of species may appear to be, we
confidently appeal to all practical naturalists, whether zoologists,
botanists, or palæontologists, to say if, in the vast majority of cases,
they know, or mean to affirm, anything more of the group of animals or
plants they so denominate than what has just been stated. Even the most
decided advocates of the received doctrines respecting species admit
this.
"I apprehend," says Professor Owen,[61] "that few naturalists
now-a-days, in describing and proposing a name for what they call
'a new _species_,' use that term to signify what was meant by it
twenty or thirty years ago; that is, an originally distinct
creation, maintaining its primitive distinction by obstructive
generative peculiarities. The proposer of the new species now
intends to state no more than he actually knows; as, for example,
that the differences on which he founds the specific character are
constant in individuals of both sexes, so far as observation has
reached; and that they are not due to domestication or to
artificially superinduced external circumstances, or to any outward
influence within his cognizance; that the species is wild, or is
such as it appears by Nature."
If we consider, in fact, that by far the largest proportion of recorded
existing species are known only by the study of their skins, or bones,
or other lifeless exuvia; that we are acquainted with none, or next to
none, of their physiological peculiarities, beyond those which can be
deduced from their structure, or are open to cursory observation; and
that we cannot hope to learn more of any of those extinct forms of life
which now constitute no inconsiderable proportion of the known Flora and
Fauna of the world: it is obvious that the definitions of these species
can be only of a purely structural or morphological character. It is
probable that naturalists would have avoided much confusion of ideas if
they had more frequently borne these necessary limitations of our
knowledge in mind. But while it may safely be admitted that we are
acquainted with only the morphological characters of the vast majority
of species--the functional, or physiological, peculiarities of a few
have been carefully investigated, and the result of that study forms a
large and most interesting portion of the physiology of reproduction.
The student of Nature wonders the more and is astonished the less, the
more conversant he becomes with her operations; but of all the perennial
miracles she offers to his inspection, perhaps the most worthy of
admiration is the development of a plant or of an animal from its
embryo. Examine the recently laid egg of some common animal, such as a
salamander or a newt. It is a minute spheroid in which the best
microscope will reveal nothing but a structureless sac, enclosing a
glairy fluid, holding granules in suspension. But strange possibilities
lie dormant in that semi-fluid globule. Let a moderate supply of warmth
reach its watery cradle, and the plastic matter undergoes changes so
rapid and yet so steady and purposelike in their succession, that one
can only compare them to those operated by a skilled modeller upon a
formless lump of clay. As with an invisible trowel, the mass is divided
and subdivided into smaller and smaller portions, until it is reduced to
an aggregation of granules not too large to build withal the finest
fabrics of the nascent organism. And, then, it is as if a delicate
finger traced out the line to be occupied by the spinal column, and
moulded the contour of the body; pinching up the head at one end, the
tail at the other, and fashioning flank and limb into due salamandrine
proportions, in so artistic a way, that, after watching the process hour
by hour, one is almost involuntarily possessed by the notion, that some
more subtle aid to vision than an achromatic, would show the hidden
artist, with his plan before him, striving with skilful manipulation to
perfect his work.
As life advances, and the young amphibian ranges the waters, the terror
of his insect contemporaries, not only are the nutritious particles
supplied by its prey, by the addition of which to its frame growth takes
place, laid down, each in its proper spot, and in such due proportion to
the rest, as to reproduce the form, the colour and the size,
characteristic of the parental stock; but even the wonderful powers of
reproducing lost parts possessed by these animals are controlled by the
same governing tendency. Cut off the legs, the tail, the jaws,
separately or all together, and, as Spallanzani showed long ago, these
parts not only grow again, but the redintegrated limb is formed on the
same type as those which were lost. The new jaw, or leg, is a newt's,
and never by any accident more like that of a frog. What is true of the
newt is true of every animal and of every plant; the acorn tends to
build itself up again into a woodland giant such as that from whose twig
it fell; the spore of the humblest lichen reproduces the green or brown
incrustation which gave it birth; and at the other end of the scale of
life, the child that resembled neither the paternal nor the maternal
side of the house would be regarded as a kind of monster.
So that the one end to which, in all living beings, the formative
impulse is tending--the one scheme which the Archæus of the old
speculators strives to carry out, seems to be to mould the offspring
into the likeness of the parent. It is the first great law of
reproduction, that the offspring tends to resemble its parent or
parents, more closely than anything else.
Science will some day show us how this law is a necessary consequence of
the more general laws which govern matter; but for the present, more can
hardly be said than that it appears to be in harmony with them. We know
that the phænomena of vitality are not something apart from other
physical phænomena, but one with them; and matter and force are the two
names of the one artist who fashions the living as well as the lifeless.
Hence living bodies should obey the same great laws as other
matter--nor, throughout Nature, is there a law of wider application than
this, that a body impelled by two forces takes the direction of their
resultant. But living bodies may be regarded as nothing but extremely
complex bundles of forces held in a mass of matter, as the complex
forces of a magnet are held in the steel by its coercive force; and,
since the differences of sex are comparatively slight, or, in other
words, the sum of the forces in each has a very similar tendency, their
resultant, the offspring, may reasonably be expected to deviate but
little from a course parallel to either, or to both.
Represent the reason of the law to ourselves by what physical metaphor
or analogy we will, however, the great matter is to apprehend its
existence and the importance of the consequences deducible from it. For
things which are like to the same are like to one another, and if, in a
great series of generations, every offspring is like its parent, it
follows that all the offspring and all the parents must be like one
another; and that, given an original parental stock, with the
opportunity of undisturbed multiplication, the law in question
necessitates the production, in course of time, of an indefinitely large
group, the whole of whose members are at once very similar and are blood
relations, having descended from the same parent, or pair of parents.
The proof that all the members of any given group of animals, or plants,
had thus descended, would be ordinarily considered sufficient to entitle
them to the rank of physiological species, for most physiologists
consider species to be definable as "the offspring of a single primitive
stock."
But though it is quite true that all those groups we call species _may_,
according to the known laws of reproduction, have descended from a
single stock, and though it is very likely they really have done so, yet
this conclusion rests on deduction and can hardly hope to establish
itself upon a basis of observation. And the primitiveness of the
supposed single stock, which, after all, is the essential part of the
matter, is not only a hypothesis, but one which has not a shadow of
foundation, if by "primitive" be meant "independent of any other living
being." A scientific definition, of which an unwarrantable hypothesis
forms an essential part, carries its condemnation within itself; but
even supposing such a definition were, in form, tenable, the
physiologist who should attempt to apply it in Nature would soon find
himself involved in great, if not inextricable difficulties. As we have
said, it is indubitable that offspring _tend_ to resemble the parental
organism, but it is equally true that the similarity attained never
amounts to identity, either in form or in structure. There is always a
certain amount of deviation, not only from the precise characters of a
single parent, but when, as in most animals and many plants, the sexes
are lodged in distinct individuals, from an exact mean between the two
parents. And indeed, on general principles, this slight deviation seems
as intelligible as the general similarity, if we reflect how complex the
co-operating "bundles of forces" are, and how improbable it is that, in
any case, their true resultant shall coincide with any mean between the
more obvious characters of the two parents. Whatever be its cause,
however, the co-existence of this tendency to minor variation with the
tendency to general similarity, is of vast importance in its bearing on
the question of the origin of species.
As a general rule, the extent to which an offspring differs from its
parent is slight enough; but, occasionally, the amount of difference is
much more strongly marked, and then the divergent offspring receives the
name of a Variety. Multitudes, of what there is every reason to believe
are such varieties, are known, but the origin of very few has been
accurately recorded, and of these we will select two as more especially
illustrative of the main features of variation. The first of them is
that of the "Ancon," or "Otter" sheep, of which a careful account is
given by Colonel David Humphreys, F.R.S., in a letter to Sir Joseph
Banks, published in the Philosophical Transactions for 1813. It appears
that one Seth Wright, the proprietor of a farm on the banks of the
Charles River, in Massachusetts, possessed a flock of fifteen ewes and a
ram of the ordinary kind. In the year 1791, one of the ewes presented
her owner with a male lamb, differing, for no assignable reason, from
its parents by a proportionally long body and short bandy legs, whence
it was unable to emulate its relatives in those sportive leaps over the
neighbours' fences, in which they were in the habit of indulging, much
to the good farmer's vexation.
The second case is that detailed by a no less unexceptionable authority
than Réaumur in his "Art de faire éclore les Poulets." A Maltese couple,
named Kelleia, whose hands and feet were constructed upon the ordinary
human model, had born to them a son, Gratio, who possessed six perfectly
moveable fingers on each hand and six toes, not quite so well formed, on
each foot. No cause could be assigned for the appearance of this unusual
variety of the human species.
Two circumstances are well worthy of remark in both these cases. In
each, the variety appears to have arisen in full force, and, as it were,
_per saltum_; a wide and definite difference appearing, at once, between
the Ancon ram and the ordinary sheep; between the six-fingered and
six-toed Gratio Kelleia and ordinary men. In neither case is it possible
to point out any obvious reason for the appearance of the variety.
Doubtless there were determining causes for these as for all other
phænomena; but they do not appear, and we can be tolerably certain that
what are ordinarily understood as changes in physical conditions, as in
climate, in food, or the like, did not take place and had nothing to do
with the matter. It was no case of what is commonly called adaptation to
circumstances; but, to use a conveniently erroneous phrase, the
variations arose spontaneously. The fruitless search after final causes
leads their pursuers a long way; but even those hardy teleologists, who
are ready to break through all the laws of physics in chase of their
favourite will-o'-the-wisp, may be puzzled to discover what purpose
could be attained by the stunted legs of Seth Wright's ram or the
hexadactyle members of Gratio Kelleia.