The idea that the human race is breeding itself stupid has received wide enough play to be the subject of science fiction stories, Margaret Sanger's nightmares, and a Mike Judge movie.
A lot of people actually take this worry quite seriously. A post on Gene Expression Classic last week about a mathematical model by I. J. Good -- which shows that (given certain assumptions) differential fertility in regard to a given trait will not necessarily result in an overall drop in the average of the population -- drew out a few commenters who thought that only wide use of genetic engineering/selection would prevent the human race from breeding itself into stupidity.
And at the less cerebral level of society, a number of the commenters on the YouTube link above also seem quite convinced that the morons are on the march.
Several things strike me about this line of thinking.
First off, some people seem to have completely equated intelligence with taking birth control. One person (in making an example about this kind of thinking) summarized the view like this: "intelligent individuals will use the Pill to restrict their births, while stupid individuals who can't obtain a prescription or comply with the instructions will not use the Pill". However, this clearly assumes a static set of cultural success factors.
At this point in time, in modern first world countries, having few or no children in order to assure maximum career flexibility and leisure time enjoyment is widely seen as a proof of "success". However, this is far from always having been the case. (Case in point, look at Charles Darwin himself, who had ten children, seven of whom lived well into adulthood. Quite a few direct descendants of Darwin are around today, many of them active and intellectual and academic life in England.)
While it's not an example of evolution per se, it certainly stands to reason that positive attitudes towards reproduction (or at least views that are not actively in conflict with the fact that humans are a biological species that survives by reproduction, not spontaneous intellectual generation) will always be selected for.
So I tend to see these fears that the "smart" people will refuse to reproduce indefinitely as unfounded. Rather, we have a situation where, at the moment, certain societal pressures and temptations have caused a large number of people with the intelligence and inclination to play the career and leisure game rather than reproducing. However, no population group is monolithic, and there are certainly plenty of highly intelligent people (though quite possibly a minority of the set as a whole) who are interested in having and rearing a decent number of children. Assuming a high degree of intelligence heritability (a whole other argument could be made -- by people with more knowledge about such things than I -- about what percentage of "highly intelligent" people can be expected in a given generation to be born of "highly intelligent" parents) it seems obvious that a much more significant percentage of the next generation or two of highly intelligent people would be the descendants of these non-reproduction-averse people -- and thus would stand a good chance of having learned different attitudes about the intersection of intellectual and family life.
Two other (perhaps somewhat contradictory) points as I wrap up:
1) It's all too easy in a closed culture (such as grad school, perhaps?) to get into thinking of intelligence as one of the highest human virtues, and holding to a pretty rigid set of ideas about how intelligence is expressed and may be identified. However, it seems to me that, given that we are and know we are a species, one must question whether it is really a sign of intelligence to think of "success" in terms that completely exclude reproduction. Knowing ourselves and our nature is supposed to be one of the marks of intelligence, and yet some ideas one hears vented about what constitutes the good life are in pretty clear contradiction to the basic biological facts of what the human species is.
2) At most time, most traits in most species are being selected towards something approaching stasis. Although it's easy to see intelligence as an unmitigated good, it may be that there is a selection factor of sorts that puts a roof on selection for intelligence. If highly intelligent people are significantly more likely to fall prey to the temptation of living strictly mental lives and ignoring the needs (including the need to perpetuate the species) of our basic human nature, that might well apply a selective force to keep average intelligence within a certain spectrum.
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