It is clear to see that in past 20 000 years, the environment in which humans live has undergone very significant change due to emergence of societies; the new environment may not be pushing us as hard, at least on the individual level.
I’m not an anthropologist, but one plausible explanation I can think of for the brain shrinkage is almost diametrically opposed to this. It’s pretty well established that early agricultural societies placed more nutritional stress on their citizens than the hunter-gatherer lifestyle that preceded them; height and various other nutritional proxies consistently went downhill after the agricultural transition and in most places didn’t make up the difference until the Renaissance or even later. Brains, as you say, are an energy-intensive piece of equipment; and agricultural productivity looks a lot less elastic with regard to intelligence than hunting or foraging. Put that together and you’ve got a pretty strong argument for negative selection pressure w.r.t brain size, at least until industrialization got rid of most nutrient constraints. I wouldn’t even be too surprised if this was responsible for part of the Flynn effect, although there are certainly other factors involved; Flynn’s working too fast for selection pressure alone.
On the other hand, the Neolithic Revolution occurred about 10,000 BP, and the linked articles talk about a timescale twice to three times that long. They’re fairly short on details, unfortunately; I can think of scenarios that’d make that consistent with my theory, but this wouldn’t by itself explain a peak at 30,000 BP.
I believe that in some cases (eyes for cave-dwelling animals? antibiotic resistance in bacteria?) a trait can be turned off rather than lost completely. This means it would be easier to get it back than to evolve it from scratch.
Good point about the higher pressure to conserve the nutrients. Essentially, it’s a matter of relative selection for whatever aspects of intelligence rely on brain size, versus the selection to conserve nutrients.
With regards to being pushed by nutrition… The population can be expected to quickly rise to equilibrium level where the nutrition limits the population. At equilibrium level, the hunters would be bigger and stronger (and perhaps brainier) than farmers, because the farmer that starved this much will survive and the hunter won’t. All while both societies have their population capped by available nutrients.
I’m not an anthropologist, but one plausible explanation I can think of for the brain shrinkage is almost diametrically opposed to this. It’s pretty well established that early agricultural societies placed more nutritional stress on their citizens than the hunter-gatherer lifestyle that preceded them; height and various other nutritional proxies consistently went downhill after the agricultural transition and in most places didn’t make up the difference until the Renaissance or even later. Brains, as you say, are an energy-intensive piece of equipment; and agricultural productivity looks a lot less elastic with regard to intelligence than hunting or foraging. Put that together and you’ve got a pretty strong argument for negative selection pressure w.r.t brain size, at least until industrialization got rid of most nutrient constraints. I wouldn’t even be too surprised if this was responsible for part of the Flynn effect, although there are certainly other factors involved; Flynn’s working too fast for selection pressure alone.
On the other hand, the Neolithic Revolution occurred about 10,000 BP, and the linked articles talk about a timescale twice to three times that long. They’re fairly short on details, unfortunately; I can think of scenarios that’d make that consistent with my theory, but this wouldn’t by itself explain a peak at 30,000 BP.
I believe that in some cases (eyes for cave-dwelling animals? antibiotic resistance in bacteria?) a trait can be turned off rather than lost completely. This means it would be easier to get it back than to evolve it from scratch.
Good point about the higher pressure to conserve the nutrients. Essentially, it’s a matter of relative selection for whatever aspects of intelligence rely on brain size, versus the selection to conserve nutrients.
With regards to being pushed by nutrition… The population can be expected to quickly rise to equilibrium level where the nutrition limits the population. At equilibrium level, the hunters would be bigger and stronger (and perhaps brainier) than farmers, because the farmer that starved this much will survive and the hunter won’t. All while both societies have their population capped by available nutrients.
The transition and preadaptation to agriculture might have taken several thousand years.
Not to mention it happened in several different places, at different times.