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blue pigeon turn up； it will be sure to have the black bars across the
wings； which are characteristic of the original wild stock； the Rock
Pigeon。
Now； this is certainly a very remarkable circumstance； but I do not see
myself how it tells very strongly either one way or the other。 I
think； in fact； that this argument in favour of recurrence to the
primitive type might prove a great deal too much for those who so
constantly bring it forward。 For example； Mr。 Darwin has very forcibly
urged； that nothing is commoner than if you examine a dun horseand I
had an opportunity of verifying this illustration lately； while in the
islands of the West Highlands； where there are a great many dun
horsesto find that horse exhibit a long black stripe down his back；
very often stripes on his shoulder； and very often stripes on his
legs。 I； myself； saw a pony of this description a short time ago； in a
baker's cart； near Rothesay； in Bute： it had the long stripe down the
back； and stripes on the shoulders and legs； just like those of the
Ass； the Quagga； and the Zebra。 Now； if we interpret the theory of
recurrence as applied to this case； might it not be said that here was
a case of a variation exhibiting the characters and conditions of an
animal occupying something like an intermediate position between the
Horse； the Ass； the Quagga； and the Zebra； and from which these had
been developed？ In the same way with regard even to Man。 Every
anatomist will tell you that there is nothing commoner； in dissecting
the human body； than to meet with what are called muscular
variationsthat is； if you dissect two bodies very carefully； you will
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 usand it is an extremely
important oneis 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 proveand this
comes to the same thingthat 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 havethough it
is not direct testimonyyet 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 deeperthey extend to the bony structure； and to the
characters of that most important of all organs to usthe 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 case of the last the breadth would be
about seven…tenths； and in the other it would be nine…tenths of the
total length。 So that you see there is abundant evidence of variation
among men in their natural condition。 And if you turn to other animals
there is just the same thing。 The fox； for example； which has a very
large geographical distribution all over Europe； and parts of Asia； and
on the American Continent； varies greatly。 There are mostly large
foxes in the North； and smaller ones in the South。 In Germany alone；
the foresters reckon some eight different sorts。
Of the tiger； no one supposes that there is more than one species； they
extend from the hottest parts of Bengal； into the dry； cold； bitter
steppes of Siberia； into a latitude of 50 degrees；so that they may
even prey upon the reindeer。 These tigers have exceedingly different
characteristics； but still they all keep their general features； so that
there is no doubt as to their being tigers。 The Siberian tiger has a
thick fur； a small mane； and a longitudinal s