Two forms of lethal selection were distinguished, one depending on
starvation and the other on causes not connected with the food supply.
Direct starvation is not a factor of importance in the survival of most
races during most of the time at the present day so far as the civilized
portion of the world is concerned. But disease and the other lethal
factors not connected with the food-supply, through which natural
selection acts, are still of great importance. From a half to two-thirds
of all deaths are of a selective character, even under favorable
conditions.
It is also to be noted, however, that with the progress of medicine, and
the diminution of unfit material, this kind of natural selection will
tend to become less and less widespread. For a long time, natural
selection in man has probably done little to cause marked change in his
physical or mental characteristics. Man's interference has prevented. In
recent centuries natural selection has probably done no more on the
whole than keep the race where it was: it is to be feared 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.
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