A couple of interesting articles just came out in MBE on how natural selection has affected human populations that ran into problems with trace elements, either too much or too little. One talked about adaptation to selenium shortages (which I’ve mentioned): this is a problem in parts of China, among other places. It seems that there has been a shift in the frequencies of variants of several genes involved in selenium metabolism – polygenic selection . The other paper discussed adaptation to high arsenic levels among people in the northern Argentinian Andes: this involved a partial selective sweep on a variant of a single gene (AS3MT) that appears to be the major gene for arsenic metabolism.
Probably there have been adaptive changes in response to iodine shortages, which are fairly widespread. In principle, shortage or oversupply could be a problem for any essential trace element; but it looks as if, in most cases, the trace element is fairly abundant in the environment (compared to the amount we need) while humans can tolerate a fair amount more than the minimum. Selenium is something of an exception: shortages and toxicity both occur.
Vitamin shortages and surpluses we know something about. I’m sure that most of my readers have learned their lesson and no longer gobble polar bear liver. It looks as if you can suffer from an ergothioneine shortage from a wheat diet, and a more-active form of the ergothioneine transporter has undergone a partial sweep in southern Europe (EEF). Interesting that dietary scientists aren’t sure what problems are caused by ergothioneine shortages: but the existence of a specific ergothioneine transporter, and that partial sweep, sh0w it does indeed do something useful. That’s a a useful approach to showing that something is useful or essential in humans, easier than putting a platitude of sophomores on a special diet and seeing if their hair falls out or they develop ED – show that there is specific molecular machinery for importing it.
I think there’s a fair chance that some populations – I’m thinking of maize and Amerindians – have adapted to poor amino acid quality: having too many of some essential amino acids and too few of others (like lysine): like Scrabble with more ‘Q’s than ‘U’s.
There might be adaptation to a cassava diet: cyanide tolerance. In South America, of course, not Africa.
There are lot of examples in which any sensible person (of which there are about five) knows that some between-population trait difference almost certainly has a genetic cause (because we always see it in every sample of that pop, in different environments) but we don’t know the genetic details, or have only a limited knowledge. For example, some populations have a lot more trouble handling alcohol than others – which, pace Robin Hanson , is genetic. We know something about the basis of this among East Asians, but I don’t think we know the genetic architecture in other populations.
What other factors that haven’t been considered at may have selected for various things in humans ? Please say something that we haven’t heard a million times before.