makes it
clear that whole groups of races now easily distinguishable from each
other, were originally one race,--that the diffusion of one race into
different climates and conditions of existence, has produced many
modified forms of it.

Similarly with domestic animals. Though in some cases--as that of
dogs--community of origin will perhaps be disputed, yet in other
cases--as that of the sheep or the cattle of our own country--it will
not be questioned that local differences of climate, food, and
treatment, have transformed one original breed into numerous breeds now
become so far distinct as to produce unstable hybrids. Moreover, through
the complications of effects flowing from single causes, we here find,
what we before inferred, not only an increase of general heterogeneity,
but also of special heterogeneity. While of the divergent divisions and
subdivisions of the human race, many have undergone changes not
constituting an advance; while in some the type may have degraded; in
others it has become decidedly more heterogeneous. The civilised
European departs more widely from the vertebrate archetype than does the
savage. Thus, both the law and the cause of progress, which, from lack
of evidence, can be but hypothetically substantiated in respect of the
earlier forms of life on our globe, can be actually substantiated in
respect of the latest forms.

If the advance of Man towards greater heterogeneity is traceable to the
production of many effects by one cause, still more clearly may the
advance of Society towards greater heterogeneity be so explained.
Consider the growth of an industrial organisation. When, as must
occasionally happen, some individual of a tribe displays unusual
aptitude for making an article of general use--a weapon, for
instance--which was before made by each man for himself, there arises a
tendency towards the differentiation of that individual into a maker of
such weapon. His companions--warriors and hunters all of
them,--severally feel the importance of having the best weapons that can
be made; and are therefore certain to offer strong inducements to this
skilled individual to make weapons for them. He, on the other hand,
having not only an unusual faculty, but an unusual liking, for making
such weapons (the talent and the desire for any occupation being
commonly associated), is predisposed to fulfil these commissions on the
offer of an adequate reward: especially as his love of distinction i