As he ranged farther from his
original home, and became exposed to greater extremes of climate, to
greater changes of food, and had to contend with new enemies, organic
and inorganic, slight useful variations in his constitution would be
selected and rendered permanent, and would, on the principle of
"correlation of growth," be accompanied by corresponding external
physical changes. Thus might have arisen those striking characteristics
and special modifications which still distinguish the chief races of
mankind. The red, black, yellow, or blushing white skin; the straight,
the curly, the woolly hair; the scanty or abundant beard; the straight
or oblique eyes; the various forms of the pelvis, the cranium, and other
parts of the skeleton.

But while these changes had been going on, his mental development had,
from some unknown cause, greatly advanced, and had now reached that
condition in which it began powerfully to influence his whole existence,
and would therefore become subject to the irresistible action of
"natural selection." This action would quickly give the ascendency to
mind: speech would probably now be first developed, leading to a still
further advance of the mental faculties; and from that moment man, as
regards the form and structure of most parts of his body, would remain
almost stationary. The art of making weapons, division of labour,
anticipation of the future, restraint of the appetites, moral, social,
and sympathetic feelings, would now have a preponderating influence on
his well being, and would therefore be that part of his nature on which
"natural selection" would most powerfully act; and we should thus have
explained that wonderful persistence of mere physical characteristics,
which is the stumbling-block of those who advocate the unity of mankind.

We are now, therefore, enabled to harmonise the conflicting views of
anthropologists on this subject. Man may have been, indeed I believe
must have been, once a homogeneous race; but it was at a period of which
we have as yet discovered no remains, at a period so remote in his
history, that he had not yet acquired that wonderfully developed brain,
the organ of the mind, which now, even in his lowest examples, raises
him far above the highest brutes;--at a period when he had the form but
hardly the nature of man, when he neither possessed human speech, nor
those sympathetic and moral feelings which in a greater or less degree
everywhere now distinguish