The Origin of Species | Page 7

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 Reaumur, in his 'Art de faire eclore 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 movable 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
phenomena; 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.

Varieties then arise we know not why; and it is more than probable that
the majority of varieties have arisen in this "spontaneous" manner,
though we are, of course, far from denying that