Man In The Modern World

MAN IN THE MODERN WORLD
perties of man. These are, for the most part, obvious and well known,
and I propose to leave them aside until I have dealt with some less
familiar human characteristics. For the human species, considered
as a species, is unique in certain purely biological attributes; and
these have not received the attention they deserve, either from the
zoological or the sociological standpoint.
In the first place, man is by far the most variable wild species
known. Domesticated species like dog, horse, or fowl may rival or
exceed him in this particular, but their variability has obvious reasons,
and is irrelevant to our inquiry.
In correlation with his wide variability, man has a far wider range
than any other animal species, with the possible exception of some of
his parasites. Man is also unique as a dominant type. All other
dominant types have evolved into many hundreds or thousands of
separate species, grouped in numerous genera, families, and larger
classificatory groups. The human type has maintained its dominance
without splitting: man's variety has been achieved within the limits
of a single species.
Finally, man is unique among higher animals in the method of his
evolution. Whereas, in general, animal evolution is divergent, human
evolution is reticulate. By this is meant that in animals, evolution
occurs by the isolation of groups which then become progressively
more different in their genetic characteristics, so that the course of
evolution can be represented as a divergent radiation of separate lines,
some of which become extinct, others continue unbranched, and still
others divergently branch again. Whereas in man, after incipient
divergence, the branches have come together again, and have gener-
ated new diversity from their Mendelian recombinations, this process
being repeated until the course of human descent is like a network.
All these biological peculiarities are interconnected. They depend
on man's migratory propensities, which themselves arise from his
fundamental peculiarities, of speech, social life, and relative independ-
ence of environment. They depend again on his capacity, when
choosing mates, for neglecting large differences of colour and appear-
ance which would almost certainly be more than enough to deter
more instinctive and less plastic animals. Thus divergence, though it
appears to have gone quite a long way in early human evolution,
generating the very distinct white, black, and yellow subspecies and
perhaps others, was never permitted to attain its normal culmination*
Mutually infertile groups were never produced: man remained a
single species. Furthermore, crossing between distinct types, which is
a rare and extraordinary phenomenon in other animals, in him