that it has
not even done that. It is doubtful if there is any race to-day which
attains the physical and mental average of the Athenians of 2,500 years
ago.

Lethal natural selection, then, has been and still is a factor of great
importance in the evolution of the race, but at present it is doing
little or nothing that promises to further the ideal of eugenics--race
betterment.

But lethal natural selection is only half the story. It is obvious that
if the constitution of a race can be altered by excess of deaths in a
certain class, it can equally be altered by excess of births in a
certain class. This is reproductive selection, which may appear in
either one of two forms. If the individual leaves few or no progeny
because of his failure to mate at the proper time, it is called sexual
selection; if, however, he mates, yet leaves few or no progeny (as
compared with other individuals), it is called fecundal selection.

Even in man, the importance of the role of reproductive selection is
insufficiently understood; in the lower animals scientists have tended
still more to undervalue it. As a fact, no species ordinarily multiplies
in such numbers as to exhaust all the food available, despite the
teaching of Malthus and Darwin to the contrary. The rate of reproduction
is the crux of natural selection; each species normally has such a
reproduction rate as will suffice to withstand the premature deaths and
sterility of some individuals, and yet not so large as to press unduly
upon the food supply. The problem of natural selection is a problem of
the adjustment between reproductive rate and death-rate, and the
struggle for subsistence is only one of several factors.

While the reproductive rate must be looked upon as a characteristic
which has its adaptations like other characteristics, it has one
peculiarity--its increase is always opposed by lethal selection. The
chances of life are reduced by reproducing, inasmuch as more danger is
entailed by the extra activities of courtship, and later, in bearing and
caring for the young, since these duties reduce the normal wariness of
individual life. The reproductive rate, therefore, always remains at the
lowest point which will suffice for the reproductive needs of the
species. For this reason alone the non-sustentative form of selection
might be expected to be the predominant kind.

J. T. Gulick and Karl Pearson have pointed out that there is a normal
conflict between natural s