The Conditions of Existence as Affecting the Perpetuation of Living Beings | Page 7

probably find that the modes of attachment and
insertion of the muscles are not exactly the same in both, there being
great peculiarities in the mode in which the muscles are arranged; and it
is very singular, that in some dissections of the human body you will
come upon arrangements of the muscles very similar indeed to the
same parts in the Apes. Is the conclusion in that case to be, that this is
like the black bars in the case of the Pigeon, and that it indicates a
recurrence to the primitive type from which the animals have been
probably developed? Truly, I think that the opponents of modification
and variation had better leave the argument of recurrence alone, or it
may prove altogether too strong for them.
To sum up,--the evidence as far as we have gone is against the
argument as to any limit to divergences, so far as structure is concerned;
and in favour of a physiological limitation. By selective breeding we
can produce structural divergences as great as those of species, but we
cannot produce equal physiological divergences. For the present I leave
the question there.
Now, the next problem that lies before us--and it is an extremely
important one--is this: Does this selective breeding occur in nature?
Because, if there is no proof of it, all that I have been telling you goes
for nothing in accounting for the origin of species. Are natural causes
competent to play the part of selection in perpetuating varieties? Here
we labour under very great difficulties. In the last lecture I had occasion
to point out to you the extreme difficulty of obtaining evidence even of
the first origin of those varieties which we know to have occurred in

domesticated animals. I told you, that almost always the origin of these
varieties is overlooked, so that I could only produce two of three cases,
as that of Gratio Kelleia and of the Ancon sheep. People forget, or do
not take notice of them until they come to have a prominence; and if
that is true of artificial cases, under our own eyes, and in animals in our
own care, how much more difficult it must be to have at first hand good
evidence of the origin of varieties in nature! Indeed, I do not know that
it is possible by direct evidence to prove the origin of a variety in
nature, or to prove selective breeding; but I will tell you what we can
prove--and this comes to the same thing--that varieties exist in nature
within the limits of species, and, what is more, that when a variety has
come into existence in nature, there are natural causes and conditions,
which are amply competent to play the part of a selective breeder; and
although that is not quite the evidence that one would like to
have--though it is not direct testimony--yet it is exceeding good and
exceedingly powerful evidence in its way.
As to the first point, of varieties existing among natural species, I might
appeal to the universal experience of every naturalist, and of any person
who has ever turned any attention at all to the characteristics of plants
and animals in a state of nature; but I may as well take a few definite
cases, and I will begin with Man himself.
I am one of those who believe that, at present, there is no evidence
whatever for saying, that mankind sprang originally from any more
than a single pair; I must say, that I cannot see any good ground
whatever, or even any tenable sort of evidence, for believing that there
is more than one species of Man. Nevertheless, as you know, just as
there are numbers of varieties in animals, so there are remarkable
varieties of men. I speak not merely of those broad and distinct
variations which you see at a glance. Everybody, of course, knows the
difference between a Negro and a white man, and can tell a Chinaman
from an Englishman. They each have peculiar characteristics of colour
and physiognomy; but you must recollect that the characters of these
races go very far deeper--they extend to the bony structure, and to the
characters of that most important of all organs to us--the brain; so that,
among men belonging to different races, or even within the same race,
one man shall have a brain a third, or half, or even seventy per cent.
bigger than another; and if you take the whole range of human brains,

you will find a variation in some cases of a hundred per cent. Apart
from these variations in the size of the brain, the characters of the skull
vary. Thus if I draw the figures of a Mongul and of a Negro head on the
blackboard, in the