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THE UNIQUENESS OF MAN
tionary point of view it represents merely the exaggeration of a
tendency which is operative in other Primates. In any case, it is a
necessary condition for the evolution and proper utilization of rational
thought. If men and women were, like mice, confronted with the
problems of adult life and parenthood after a few weeks, or even, like
whales, after a couple of years, they could never acquire the skills of
body and mind that they now absorb from and contribute to the
social heritage of the species.
This slowing (or "foetalization," as Bolk has called it, since it pro-
longs the foetal characteristics of earlier ancestral forms into postnatal
development and even into adult life) has had other important by-
products for man. Here I will mention but one—his nakedness. The
distribution of hair on man is extremely similar to that on a late foetus
of a chimpanzee, and there can be little doubt that it represents an
extension of this temporary anthropoid phase into permanence.
Hairlessness of body is not a unique biological characteristic of man;
but it is unique among terrestrial mammals, save for a few desert
creatures, and some others which have compensated for loss of hair by
developing a pachydermatous skin. In any case, it has important
biological consequences, since it must have encouraged the com-
paratively defenceless human creatures in their efforts to protect
themselves against animal enemies and the elements, and so has been
a spur to the improvement of intelligence.
Now, foetalization could never have occurred in a mammal pro-
ducing many young at a time, since intra-utcrine competition would
have encouraged the opposing tendency. Thus we may conclude that
conceptual thought could develop only in a mammalian stock which
normally brings forth but one young at a birth. Such a stock is
provided in the Primates—lemurs, monkeys, and apes.
The Primates also have another characteristic which was necessary
for the ancestor of a rational animal—they are arboreal. It may seem
curious that living in trees is a prerequisite of conceptual thought.
But Elliot Smith's analysis has abundaxitly shown that only in an
arboreal mammal could the forelimb become a true hand, and sight
become dominant over smell. Hands obtain an elaborate tactile
pattern of what they handle, eyes an elaborate visual pattern of what
they see. The combination of the two kinds of pattern, with the aid
of binocular vision, in the higher centres of the brain allowed the
Primate to acquire a wholly new richness of knowledge about objects,
a wholly new possibility of manipulating them. Tree life laid the
foundation both for the fuller definition of objects by conceptual
thought and for the fuller control of them by tools and machines.