All very true. There's a lot of factors in play for most of biology, so I wouldn't narrow it down to one thing. IQ, height, weight, etc. all are determined by an interaction of many genes, as well as many environmental factors. But I wanted to point why IQ and weight are linked on average, despite exceptions to the trend. Without a doubt, some people have greater genetic propensity to put on weight while eating a modern diet, which today is loaded with sugar or HFCS, preservatives, dyes, etc. as well as lacking nutrients. Also, everyone is sitting much more than we used to, but office work tends to be for the right end of the IQ been curve. Our ability to tolerate these modern poisons is not equally weighted, nor is our exposure to it. But it's still more likely that someone smarter is likely to figure out these dangers and find a solution, all else being equal. As for the rest, R/K reproductive strategies explain a lot. It's linked to IQ, but not perfectly. Someone can be smart but still follow the R strategy, like Genghis Khan. But speaking in broad strokes, races seem to have their own personality that's outside of IQ. Whites are very trusting, cooperative, individualistic but also ideologically driven ("do the right thing" even if it's detrimental). Asians are less trusting, practical, family oriented, non-ideological, and often very technically skilled. According to modern tests the asians have a slight IQ lead, but the majority of scientific and industrial advancements can be attributed to whites. Asia was much richer and more populous than Europe for much of it's history, so something biologically rooted is likely at play that lead to such different outcomes.