Intelligence tests indicate that average population intelligence might have increased over the last century.
These tests are very flawed and should not be taken as scientific evidence, but it might be good enough for trend observations. The assumed explanation for this rise is better nutrition and more intellectually stimulating environments.
Intelligence is not self defeating from an evolutionary perspective. Stephen Hawkins for example, was a very intelligent physicist, but he couldn't have survived in any other period of history, because it took a lot of technology to keep him going, proving that intelligent people create a world that benefits the survival of intelligent people.
Capitalism is probably trying to commodify the general intellect, (humanities collective knowledge and technical know how) and that could fracture the knowledge base and cause a decline in the technological level. There might be a counteracting force, if capitalist governments become too tyrannical with persecuting bogus thought crimes like "intellectual property" they will undermine their power and influence by hampering their technical base that is the foundation of projecting influence. So that free and open knowledge system always win over closed ones.
About the biological factors, there are statistical factors at play. If you have a large population size, your chances of having a lot of intelligent people rises as well. Increasing the population size is a more effective way of increasing the absolute number of intelligent people than any kind of eugenics program, where you kill off or sterilize un-inteligent people. What counts for technological progress is the absolute number of intelligent people working towards advancing the means of production , not the ratio of intelligent people in the population.
Eugenics is a dumb idea because, if you propose weeding out the "low quality people" it's in the interest of everybody to kill you off preemptively, because you are telling everybody that you are a potential risk to their survival or evolutionary success. Nobody will believe any test scores you come up with and instead attribute a bad result to malicious intentions or incompetence on your part. Most people will agree to kill off the guy who might be questioning their right to live or have kids. Don't be that guy.
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