I'm of the persuasion that the average intelligence and physical health of a homogenous population is most influenced by epigenetics, developmental nutrition, and environment. Epigenetics definitely being a very strong factor.
I have friends that have 1/8 to 1/4 ancestry from areas of the world that likely were abundant in nutrition, sun, and nature for the last few centuries. They have very robust health despite not thinking about nutrition or exercise at all.
I also have friends that grew up on farms. Daily sun, farm fresh milk, meat, potatoes, exercise, outdoor play in nature every single day of their childhood. One of these friends, who is white, is especially ripped and extremely muscular with very little exercise and just simply eating whatever throughout the day.
Every living human today has common ancestors probably in the last 50,000 years and many within the last 5,000 years. I don't think we are all that different genetically, but epigenetically and environmentally there are some significant differences based on the economics and migrations of the last few hundred years.
Intellectual capacity seems to be largely influenced by how stimulating the early childhood years are. Those who learn several languages before 5 years old have an entirely different mental foundation than those who can barely speak and understand one. In many un-modernized areas of the world it is common for people to have strong ability to think and speak in many languages.