| Both Sexes (Averaged) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Grades for virtues | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Average number of adult children. | 1.66 | 2.86 | 2.99 | 2.41 | 3.44 | 3.49 | 3.05 | 3.03 | 3.93 | 3.83 |
Investigations of Karl Pearson and Alexander Graham Bell21 show that fecundity and longevity are associated. It follows that the mentally and morally superior, who are the most fecund, are also the longest-lived; and as this longevity is largely due to inheritance it follows that, under natural conditions, the standard of the stratum of society under consideration would gradually rise, in respect to longevity, in each generation.
Such is probably one of the methods by which the human race has gradually increased its level of desirable characters in each generation. The desirable characters were associated with each other, and also with fecundity. The desirable characters are still associated with each other, but their association with fecundity is now negative. It is in this change that eugenics finds justification for its existence as a propaganda. Its object is to restore the positive correlation between desirable characters and fecundity, on which the progressive evolution of the race depends.
The bearing of natural selection on the present-day evolution of the human race, particularly in the United States of America, must be reviewed in a few closing paragraphs.
Selection by death may result either from inadequate food supply, or from some other lethal factor. The former type, although something of a bugaboo ever since the time of Malthus, has in reality relatively little effect on the human race at present. Non-sustentative lethal selection in man is operating chiefly through zymotic diseases and the bad hygiene of the mentally inferior.