generalizations which facilitated the understanding of man's
origin. But he did not come at all near to solving the central
problem, nor did he anywhere show clearly why natural selection
might not have gone on forever producing one set of beings after
another distinguishable chiefly by physical differences. But
Darwin's co-discoverer, Alfred Russel Wallace, at an early stage in
his researches, struck out a most brilliant and pregnant
suggestion. In that one respect Wallace went further than ever
Darwin did. It was a point of which, indeed, Darwin admitted the
importance. It was a point of which nobody could fail to
understand the importance, that in the course of the evolution of a
very highly organized animal, if there came a point at which it was
of more advantage to that animal to have variations in his
intelligence seized upon and improved by natural selection than to
have physical changes seized upon, then natural selection would
begin working almost exclusively upon that creature's intelligence,
and he would develop in intelligence to a great extent, while his
physical organism would change but slightly. Now, that of course
applied to the case of man, who is changed physically but very
slightly from the apes, while he has traversed intellectually such
a stupendous chasm.

As soon as this statement was made by Wallace, it seemed to me to
open up an entirely new world of speculation. There was this
enormous antiquity of man, during the greater part of which he did
not know enough to make history. We see man existing here on the
earth, no one can say how long, but surely many hundreds of
thousands of years, yet only during just the last little fringe of
four or five thousand years has he arrived at the point where he
makes history. Before that, something was going on, a great many
things were going on, while his ancestors were slowly growing up to
that point of intelligence where it began to make itself felt in
the recording of events. This agrees with Wallace's suggestion of
a long period of psychical change, accompanied by slight physical
change.

Well, in the spring of 1871, when Darwin's "Descent of Man" came
out, just about the same time I happened to be reading Wallace's
account of his experiences in the Malay Archipelago, and how at one
time he caught a female orang-outang with a new-born baby, and the
mother died, and Wallace brought up the baby orang-outang by hand;
and this baby orang-outang