_The Central Fact in the Genesis of Man_
This conclusion, which follows irresistibly from Wallace's theorem, that
in the genesis of Humanity natural selection began to follow a new path,
already throws a light of promise over our whole subject, like the rosy
dawn of a June morning. But the explanation of the genesis of Humanity
is still far from complete. If we compare man with any of the higher
mammals, such as dogs and horses and apes, we are struck with several
points of difference: _first_, the greater progressiveness of man, the
widening of the interval by which one generation may vary from its
predecessor; _secondly_, the definite grouping in societies based on
more or less permanent family relationships, instead of the indefinite
grouping in miscellaneous herds or packs; _thirdly_, the possession of
articulate speech; _fourthly_, the enormous increase in the duration of
infancy, or the period when parental care is needed. Twenty-four years
ago, in a course of lectures given yonder in Holden Chapel, I showed
that the circumstance last named is the fundamental one, and the others
are derivative. It is the prolonged infancy that has caused the
progressiveness and the grouping into definite societies, while the
development of language was a consequence of the increasing intelligence
and sociality thus caused. In the genesis of Humanity the central fact
has been the increased duration of infancy. Now, can we assign for that
increased duration an adequate cause? I think we can. The increase of
intelligence is itself such a cause. A glance at the animal kingdom
shows us no such thing as infancy among the lower orders. It is with
warm-blooded birds and mammals that the phenomena of infancy and the
correlative parental care really begin.
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