Working through my reading pile, I finally read this great 1966 article by James Crow - The Quality of People: Human Evolutionary Changes. For those unfamiliar with Crow’s work, it’s worth watching this piece from Wisconsin Public Television (HT: Steve Hsu). The introduction captures some of his achievements.
In the paper, Crow opens by discussing the prediction of future evolutionary trends for humans:
Prediction of future evolutionary trends is difficult because man himself plays such a decisive role. The largest influence in man’s future is man himself - the things that the individual and society do, intentionally or unwittingly. Yet, some trends are clear. Bacterial and protozoon diseases have been drastically reduced in many parts of the world. A few decades ago a gene producing a decreased susceptibility to smallpox would have had a great selective advantage. Now, in much of the world such a gene is of little value. We can expect that throughout the world selection for resistance to infection will become less and less important. …
The greater mobility of contemporary populations will also have genetic consequences. There is certain to be less inbreeding as persons tend to find mates away from their home environs. This should decrease the incidence of rare recessive diseases and cause some increase in general health and vigor - although the latter may not be measurable directly.
A second consequence of mobility may be enhanced degree of assortive marriage. The greater participation in higher education, the stratification of students by aptitude, the growth of communities with similar interests and attainments all can lead to increased correlations between husband and wife. Added to this is the greater range of choice created by affluence and mobility so that any inherent preferences for assortative marriage are more easily realized.
The effect of assortative marriage is to increase the population variability. There is already a high correlation in IQ between husband and wife, and this may well increase. To the extent that this trait is heritable there will be greater variability next generation than would otherwise be the case. This means more geniuses as well as more at the other end of the scale.
After discussing the rate of human evolution (in many dimensions slow) and the potential for selection in human societies as death rates decline (large enough that considerable selection can still occur), Crow moves to the question of eugenics. One of his more interesting points concerns the purpose of eugenics.
An immediate difficulty is to avoid the bias of our own society. What constitutes a good phenotype is not likely to be thought to be the same in Africa, China, and Greenland. …
Crow also foreshadows the challenges that the development of genetic technologies will present in the future.
It is clear that biological and chemical possibilities for influencing human evolution and development are certain to come, probably before we have thought them through. Eugenics could be a far more potent force in the future than previously. In the past it has been tolerated partly because it was not likely to make an appreciable genetic change. The early eugenics was genetically naive and was connected with various dubious and even tragic political movements. I think the time is here when the subject should be reopened and discussed by everyone – not just biologists - with a serious consideration of the consequences of misjudgments as well as the possibilities for good.
Over 40 years later, those possibilities are starting to crystallise (particularly with the rise of positive eugenics). The serious consideration is still to come.