[_Originally published in _The Leader, _for March 20,_ 1852. _Brief
though it is, I place this essay before the rest, partly because
with the exception of a similarly-brief essay on "Use and Beauty",
it came first in order of time, but chiefly because it came first in
order of thought, and struck the keynote of all that was to
follow._]
In a debate upon the development hypothesis, lately narrated to me by a
friend, one of the disputants was described as arguing that as, in all
our experience, we know no such phenomenon as transmutation of species,
it is unphilosophical to assume that transmutation of species ever takes
place. Had I been present I think that, passing over his assertion,
which is open to criticism, I should have replied that, as in all our
experience we have never known a species _created_, it was, by his own
showing, unphilosophical to assume that any species ever had been
created.
Those who cavalierly reject the Theory of Evolution as not being
adequately supported by facts, seem to forget that their own theory is
supported by no facts at all. Like the majority of men who are born to a
given belief, they demand the most rigorous proof of any adverse belief,
but assume that their own needs none. Here we find, scattered over the
globe, vegetable and animal organisms numbering, of the one kind
(according to Humboldt), some 320,000 species, and of the other, some
2,000,000 species (see Carpenter); and if to these we add the numbers of
animal and vegetable species which have become extinct, we may safely
estimate the number of species that have existed, and are existing, on
the Earth, at not less than _ten millions_. Well, which is the most
rational theory about these ten millions of species? Is it most likely
that there have been ten millions of special creations? or is it most
likely that, by continual modifications due to change of circumstances,
ten millions of varieties have been produced, as varieties are being
produced still?
Doubtless many will reply that they can more easily conceive ten
millions of special creations to have taken place, than they can
conceive that ten millions of varieties have arisen by successive
modifications. All such, however, will find, on inquiry, that they are
under an illusion. This is one of the many cases in which men do not
really believe, but rather _believe they believe_. It is not that they
can truly conceive ten millions of special creations to have taken
place, but that they _think they can do so_. Careful introspection will
show them that they have never yet realized to themselves the creation
of even _one_ species. If they have formed a definite conception of the
process, let them tell us how a new species is constructed, and how it
makes its appearance. Is it thrown down from the clouds? or must we hold
to the notion that it struggles up out of the ground? Do its limbs and
viscera rush together from all the points of the compass? or must we
receive the old Hebrew idea, that God takes clay and moulds a new
creature? If they say that a new creature is produced in none of these
modes, which are too absurd to be believed, then they are required to
describe the mode in which a new creature _may_ be produced--a mode
which does _not_ seem absurd; and such a mode they will find that they
neither have conceived nor can conceive.
Should the believers in special creations consider it unfair thus to
call upon them to describe how special creations take place, I reply
that this is far less than they demand from the supporters of the
Development Hypothesis. They are merely asked to point out a
_conceivable_ mode. On the other hand, they ask, not simply for a
_conceivable_ mode, but for the _actual_ mode. They do not say--Show us
how this _may_ take place; but they say--Show us how this _does_ take
place. So far from its being unreasonable to put the above question, it
would be reasonable to ask not only for a _possible_ mode of special
creation, but for an _ascertained_ mode; seeing that this is no greater
a demand than they make upon their opponents.
And here we may perceive how much more defensible the new doctrine is
than the old one. Even could the supporters of the Development
Hypothesis merely show that the origination of species by the process of
modification is conceivable, they would be in a better position than
their opponents. But they can do much more than this. They can show that
the process of modification has effected, and is effecting, decided
changes in all organisms subject to modifying influences. Though, from
the impossibility of getting at a sufficiency of facts, they are unable
to trace the many phases through which any existing species has passed
in arriving at its present form, or to identify the influences which
caused the successive modifications; yet, they can show that any
existing species--animal or vegetable--when placed under conditions
different from its previous ones, _immediately begins to undergo certain
changes fitting it for the new conditions_. They can show that in
successive generations these changes continue; until, ultimately, the
new conditions become the natural ones. They can show that in cultivated
plants, in domesticated animals, and in the several races of men, such
alterations have taken place. They can show that the degrees of
difference so produced are often, as in dogs, greater than those on
which distinctions of species are in other cases founded. They can show
that it is a matter of dispute whether some of these modified forms are
varieties or separate species. They can show, too, that the changes
daily taking place in ourselves--the facility that attends long
practice, and the loss of aptitude that begins when practice ceases--the
strengthening of passions habitually gratified, and the weakening of
those habitually curbed--the development of every faculty, bodily,
moral, or intellectual, according to the use made of it--are all
explicable on this same principle. And thus they can show that
throughout all organic nature there _is_ at work a modifying influence
of the kind they assign as the cause of these specific differences: an
influence which, though slow in its action, does, in time, if the
circumstances demand it, produce marked changes--an influence which, to
all appearance, would produce in the millions of years, and under the
great varieties of condition which geological records imply, any amount
of change.
Which, then, is the most rational hypothesis?--that of special creations
which has neither a fact to support it nor is even definitely
conceivable; or that of modification, which is not only definitely
conceivable, but is countenanced by the habitudes of every existing
organism?
That by any series of changes a protozoon should ever become a mammal,
seems to those who are not familiar with zoology, and who have not seen
how clear becomes the relationship between the simplest and the most
complex forms when intermediate forms are examined, a very grotesque
notion. Habitually looking at things rather in their statical aspect
than in their dynamical aspect, they never realize the fact that, by
small increments of modification, any amount of modification may in time
be generated. That surprise which they feel on finding one whom they
last saw as a boy, grown into a man, becomes incredulity when the degree
of change is greater. Nevertheless, abundant instances are at hand of
the mode in which we may pass to the most diverse forms by insensible
gradations. Arguing the matter some time since with a learned professor,
I illustrated my position thus:--You admit that there is no apparent
relationship between a circle and an hyperbola. The one is a finite
curve; the other is an infinite one. All parts of the one are alike; of
the other no parts are alike [save parts on its opposite sides]. The one
incloses a space; the other will not inclose a space though produced for
ever. Yet opposite as are these curves in all their properties, they may
be connected together by a series of intermediate curves, no one of
which differs from the adjacent ones in any appreciable degree. Thus, if
a cone be cut by a plane at right angles to its axis we get a circle.
If, instead of being perfectly at right angles, the plane subtends with
the axis an angle of 89 deg. 59', we have an ellipse which no human eye,
even when aided by an accurate pair of compasses, can distinguish from a
circle. Decreasing the angle minute by minute, the ellipse becomes first
perceptibly eccentric, then manifestly so, and by and by acquires so
immensely elongated a form, as to bear no recognizable resemblance to a
circle. By continuing this process, the ellipse passes insensibly into a
parabola; and, ultimately, by still further diminishing the angle, into
an hyperbola. Now here we have four different species of curve--circle,
ellipse, parabola, and hyperbola--each having its peculiar properties
and its separate equation, and the first and last of which are quite
opposite in nature, connected together as members of one series, all
producible by a single process of insensible modification.
But the blindness of those who think it absurd to suppose that complex
organic forms may have arisen by successive modifications out of simple
ones, becomes astonishing when we remember that complex organic forms
are daily being thus produced. A tree differs from a seed immeasurably
in every respect--in bulk, in structure, in colour, in form, in chemical
composition: differs so greatly that no visible resemblance of any kind
can be pointed out between them. Yet is the one changed in the course of
a few years into the other: changed so gradually, that at no moment can
it be said--Now the seed ceases to be, and the tree exists. What can be
more widely contrasted than a newly-born child and the small,
semi-transparent spherule constituting the human ovum? The infant is so
complex in structure that a cyclopaedia is needed to describe its
constituent parts. The germinal vesicle is so simple that it may be
defined in a line. Nevertheless a few months suffice to develop the one
out of the other; and that, too, by a series of modifications so small,
that were the embryo examined at successive minutes, even a microscope
would with difficulty disclose any sensible changes. That the uneducated
and the ill-educated should think the hypothesis that all races of
beings, man inclusive, may in process of time have been evolved from the
simplest monad, a ludicrous one, is not to be wondered at. But for the
physiologist, who knows that every individual being _is_ so evolved--who
knows, further, that in their earliest condition the germs of all plants
and animals whatever are so similar, "that there is no appreciable
distinction amongst them, which would enable it to be determined whether
a particular molecule is the germ of a Conferva or of an Oak, of a
Zoophyte or of a Man;"[1]--for him to make a difficulty of the matter is
inexcusable. Surely if a single cell may, when subjected to certain
influences, become a man in the space of twenty years; there is nothing
absurd in the hypothesis that under certain other influences, a cell
may, in the course of millions of years, give origin to the human race.
We have, indeed, in the part taken by many scientific men in this
controversy of "Law _versus_ Miracle," a good illustration of the
tenacious vitality of superstitions. Ask one of our leading geologists
or physiologists whether he believes in the Mosaic account of the
creation, and he will take the question as next to an insult. Either he
rejects the narrative entirely, or understands it in some vague
nonnatural sense. Yet one part of it he unconsciously adopts; and that,
too, literally. For whence has he got this notion of "special
creations," which he thinks so reasonable, and fights for so vigorously?
Evidently he can trace it back to no other source than this myth which
he repudiates. He has not a single fact in nature to cite in proof of
it; nor is he prepared with any chain of reasoning by which it may be
established. Catechize him, and he will be forced to confess that the
notion was put into his mind in childhood as part of a story which he
now thinks absurd. And why, after rejecting all the rest of the story,
he should strenuously defend this last remnant of it, as though he had
received it on valid authority, he would be puzzled to say.