in self-criticism: "The views here advanced, on
the part which sexual selection has played in the history of man, want
scientific precision."[108] I need here only point out that it is
impossible to explain the graduated stages of skin-colour by sexual
selection, since it would have produced races sharply defined by their
colour and not united to other races by transition stages, and this,
it is well known, is not the case. Moreover, the fact established by
me,[109] that in all races the ventral side of the trunk is paler than
the dorsal side, and the inner surface of the extremities paler than
the outer side, cannot be explained by sexual selection in the
Darwinian sense.

With this I conclude my brief survey of the rich contents of Darwin's
book. I may be permitted to conclude by quoting the magnificent final
words of _The Descent of Man_: "We must, however, acknowledge, as it
seems to me, that man, with all his noble qualities, with sympathy
which feels for the most debased, with benevolence which extends not
only to other men but to the humblest living creature, with his
god-like intellect which has penetrated into the movements and
constitution of the solar system--with all these exalted powers--Man
still bears in his bodily frame the indelible stamp of his lowly
origin."[110]

What has been the fate of Darwin's doctrines since his great
achievement? How have they been received and followed up by the
scientific and lay world? And what do the successors of the mighty
hero and genius think now in regard to the origin of the human race?

At the present time we are incomparably more favourably placed than
Darwin was for answering this question of all questions. We have at
our command an incomparably greater wealth of material than he had at
his disposal. And we are more fortunate than he in this respect, that
we now know transition-forms which help to fill up the gap, still
great, between the lowest human races and the highest apes. Let us
consider for a little the more essential additions to our knowledge
since the publication of _The Descent of Man_.

Since that time our knowledge of animal embryos has increased
enormously. While Darwin was obliged to content himself with comparing
a human embryo with that of a dog, there are now available the
youngest embryos of monkeys of all possible groups (Orang, Gibbon,
Semnopithecus, Macacus), thanks to Selenka's most successful tour in
the East Indies in search of such m