> if it were true, we would see all sorts of genetic correlations where one good trait systematically boosts a bad trait. This is almost never true I see it as

> if it were true, we would see all sorts of genetic correlations where one good trait systematically boosts a bad trait. This is almost never true I see it as almost axiomatically true, but I think the difference is you are taking a narrow definition of what constitutes a "bad" trait. Examples: - Immune system: protects us from microbes but contributes to atherosclerosis, autoimmunity, and age-associated chronic inflammation - Mitochondria: Generates ATP but also oxidative stress - Infant brain size: makes humans as smart as we are but increases maternal mortality - Body mass/volume: gives greater protection against predation but increases energy requirements - Intelligence & brain volume: improves on-the-fly adaptability but costs a lot of energy to run In the most general case, any gain-of-function adaptation which adds a new protein/organelle/limb/etc has a built-in bad trait which is that it costs resources to produce, DNA to maintain, and also adds another potential point of failure. The equilibrium point between benefit and costs is where evolution will land. So I would argue that the reason we have X IQ points or Y neurons is exactly the same reason we have Z mitochondria: any more and the costs would have exceeded the benefits in the ancestral environment. The fact that we can seemingly get more benefits than costs from increased intelligence now merely reflects the fact that our environment has changed. Also, JBS Haldane wrote an anti-eugenics book many years ago which used exactly this sort of argument.