Why would we assume a universal selection pressure across a continent spanning dozens of biomes, pretty much none of which are unique to it, and with large geographic distribution such as to produce dozens if not hundreds of distinct population groups?
A universal selection pressure doesn’t produce dozens of distinct population groups, it would homogenize them. What would help produce distinct population groups—in addition to the genetic drift and inherent random walk behavior of all partially or wholly separated population groups with non-panmictic mating behavior which would produce large differences anyway—is different selection pressures for different things in different places, potentially varying over time due to environmental and social changes. (Such as, to name one possibility, greater disease burden making intelligence less fit compared to diverting those metabolic resources into faster maturation or more robust immune systems.) Since the Arctic is not Asia is not Africa, there is no surprise that there might be different selection pressures, and the real question is why one would expect selection pressures to be universally identical such that evolution would stop at the neck.
Since the Arctic is not Asia is not Africa, there is no surprise that there might be different selection pressures, and the real question is why one would expect selection pressures to be universally identical such that evolution would stop at the neck.
The real question is why you think selection pressures in Africa, which is an extraordinarily diverse continent, would be universally identical such that evolution would stop at the neck. You keep bringing up “disease burden”—okay, I’ll bite. What’s your evidence that disease burden was substantially different in Africa, as a whole, than anywhere else prior to industrialization?
What’s your evidence that disease burden was substantially different in Africa, as a whole, than anywhere else prior to industrialization?
This is not a controversial point. Warmer and tropical climates have always had higher parasite and disease loads than colder ones. If you disagree with basic stuff like this, the burden is on you.
Although in this case the relevant factor is that since humans originally evolved in Africa, it had more diseases that co-evolved with humans. Hence why South America, which has a cilmate similar to Africa had an even lower disease burden than Europe. At least until Europeans brought Africans, some of whom were infected with African diseases there.
Why would you ever assume that selection pressures were absent?
Why would we assume a universal selection pressure across a continent spanning dozens of biomes, pretty much none of which are unique to it, and with large geographic distribution such as to produce dozens if not hundreds of distinct population groups?
A universal selection pressure doesn’t produce dozens of distinct population groups, it would homogenize them. What would help produce distinct population groups—in addition to the genetic drift and inherent random walk behavior of all partially or wholly separated population groups with non-panmictic mating behavior which would produce large differences anyway—is different selection pressures for different things in different places, potentially varying over time due to environmental and social changes. (Such as, to name one possibility, greater disease burden making intelligence less fit compared to diverting those metabolic resources into faster maturation or more robust immune systems.) Since the Arctic is not Asia is not Africa, there is no surprise that there might be different selection pressures, and the real question is why one would expect selection pressures to be universally identical such that evolution would stop at the neck.
The real question is why you think selection pressures in Africa, which is an extraordinarily diverse continent, would be universally identical such that evolution would stop at the neck. You keep bringing up “disease burden”—okay, I’ll bite. What’s your evidence that disease burden was substantially different in Africa, as a whole, than anywhere else prior to industrialization?
This is not a controversial point. Warmer and tropical climates have always had higher parasite and disease loads than colder ones. If you disagree with basic stuff like this, the burden is on you.
Although in this case the relevant factor is that since humans originally evolved in Africa, it had more diseases that co-evolved with humans. Hence why South America, which has a cilmate similar to Africa had an even lower disease burden than Europe. At least until Europeans brought Africans, some of whom were infected with African diseases there.
You might want to look at Africa on a map, because it isn’t all tropical.
You seem to be thinking of Africa as a tiny place with uniform geography and climate and biome—it’s not.