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Africa, parasites, intelligence


To understand intelligence in the tropics, e.g. among dark-skinned Africans, you need to understand the importance of parasites—both as an environmental factor that exerts a negative effect on mental development and a positive effect on selection for biological diversity of all sorts, including intelligence.

1.  Taking first the well-known negative effect of parasite load on individual intelligence—in the US the parallel factor is toxins and also indoor parasites, as in tenements—the US is now more segregated by race than it was in 1965 and so that many studies show that there is a strong tendency for whites to live in healthy environments and blacks inferior habitats.

For Africa, the environmental factor is parasites—disease—known to exert a strong negative effect on intelligence.

They also exert a very strong positive effect for genetic diversity in their hosts that may in turn select for some groups excelling in intelligence, even if the mean is lower—variance is higher.

2--Hominids have always emerged from Africa, erectus, sapiens, sapiens neanderthalensis and sapiens sapiens, but with trivial exceptions never in the reverse direction--why? Because Africa is the most genetically variable part of the world, especially the smaller the organism, hence parasites. African human populations are invariably more genetically variable than more temperate hominids, including today.

The same rule applies more generally, that is, to almost all species—migration is always tropics to temperate to arctic, rarely the other way around (e.g. salamanders are the exception: temperate to tropics)—it is Mexicans and people further south who are coming into the US, not Canadians and Eskimos. So Trump is erecting a barrier against Darlington’s Rule—migration is always tropics outward.  Africa is the center of the tropics in the entire globe. Before that it was part of Gondwanaland (Africa, South America, Antarctic) but it was the center of that super-continent, and therefore most tropical section, so Darlington’s rule held back then, as we know from fossils.




BTW it is striking that there is strong evidence that selection from parasites has been increasing over the past 40,000 years with an acceleration of positive selection to a striking degree—before agriculture and animal husbandry which added further acceleration associated with orders of magnitude (5 0r 6) increases in density. There are “signatures” that genes show of recent strong positive selection, basically comparing neutral sites (change in DNA has no effect on structure of associated protein) with non-neutral sites and seeing if the latter evolve while the former show a random walk.

And what are the chief “selected variants”?  Parasite-resistant genes.

Now these are automatically selected when density increases because parasites LOVE density--consider people packed in a room breathing on each other, or water-born parasites traveling quickly to others, or vector-borne parasites, e.g. malaria--if one in ten humans are sick but widely dispersed a mosquito biting the sick person rarely passes on the Plasmodium but if dense, every tenth person gives it to the mosquito who quickly passes it on

Likewise parasites like mobility--which increases density of contacts--so Haitians acquired HIV-1 because their middle class served as the middle class of emerging French-speaking African nations with high HIV, and they brought back the disease with them when they returned (though of course not whatever HIV-resistant genes may have been selected among the Africans).

Divergent human populations often show very similar patterns of strong selection for genes though different in time--thus Europe and Yoruba-land showed similar peaks in parasite resistant selection, though 10,000 years ago in the former and 8500 in the latter

Incidentally very striking that cases of strong outbreeding, e.g between sapiens and neanderthalensis resulted in us acquiring ~3% of our genome from them, half were local-environment genes—fair skin, less hair on back, blue eyes and red hair on head—and half PARASITE-RESISTANT GENES (MHC genes).

Likewise interbreeding between 'us' and Denisovens in Tibet helped us acquire alleles uniquely suited for high altitude and, once again, resistance to local parasites.

Logic is obvious--if you are moving into Europe for the first time you are adapted to the parasites from which you came (malaria, yellow fever, dengue fever, this that and the third African disease) but not those in the area you are invading (smallpox, the plague)

3--Human genetic diversity declines as people move from Africa outwards--why? Serial founder effect.  It is always a sub-group of the larger group that decides to go over the next mountain and colonize the valley. They can rapidly reconstitute numbers but not lost genetic diversity—repeated over and over you see a steady decline in genetic diversity from Africa to mid-East Europe Asia (Russia) and finally into arctic America and right down to southern America within ~1000 generations

Hence Amerindians highly vulnerable to invasion of Europeans + Africans, bringing in small-pox, the plague, malaria, dengue fever to which they were highly vulnerable. Ever see pictures of adult Indians with their entire outer skin peeling off as they died hideous deaths from smallpox? Did you know that part of the genocide was to pass out ‘smallpox blankets’ from infected English children to Indian mothers? It is estimated that ½ of all Indians were slaughtered and the other ½ killed by parasites.

And let us go back in time. Did the burst in cave art (40,000 years ago) have anything to do with sexual selection related to increase in density and parasites—or is art unrelated to music? BTW recent analysis based on 2nd/4th digit ratio suggests the possibility that the artists were females!  Indeed for that matter what is the relationship between song, dance and intelligence? Especially in social interactions.

4.  And what is special about Jewish intelligence? Surely it is that it emerged in a mercantile settings, natural home of numbers, logic and mathematics—itself the “gateway to knowledge”, so huge disproportion of Nobel Prizes to go those of Jewish ancestry—half-Jews specially Bill Hamilton said to me in 1979 and I always regretted not saying to him “So where are the Jewish genes in you?”

BTW Ernst Mayr argued that the Jewish religion promoted intellectual reproduction, by encouraging the Rabbi to have the biggest family, while of course the Catholics emasculated their clergy