One thing that I often hear in relation to human brain size is that the upper bound of our brain size is limited by the need for the brain to get through the pelvis during birth.
However, if this were the case, it seems that in equilibrium there should be a number of mutations which increase brain size (and by extension, intelligence), but these variants would be bounded in frequency by their negative effect on maternal survival (and which could provide low hanging fruit for intelligence selection in the modern world since survivability of difficult births is much higher with e.g. blood transfusions and c-sections).
However, as far as I can tell, there aren't genes which have this large effect, and IQ isn't a major predictor of difficult labour (though I haven't searched too much and I've no expertise in the area). Do you know what the error is here?
I find this important because it's part of the question of whether human intelligence rose continuously until we hit a critical point at which civilization exploded into life, or whether we were at some kind of long-term plateau and the core change was just a slow accumulation of physical, intellectual and social technologies until a positive feedback loop could take hold.
I've often heard and read that too, but human brains grow more after birth than brains of other species of primates. The need for the brain to pass through the pelvis at childbirth appears to have reached a tradeoff in pre-human apes causing them to have their babies prematurely; and humans to give birth even more prematurely than chimpanzees.
The fontanelles also significantly reduce the degree to which human brain size, in particular, rather than birth weight of the infant's whole body is correlated with the severity of childbirth. (Unfused fontanelles at birth are another trait humans share with apes, but not other mammals.)
Given that human brains do most of their growth after birth and the radius required for a brain to pass through the birth canal is somewhat decoupled from brain size in humans; I would guess that other factors like calorie availability have had a bigger impact on limiting adult human brain size than birth constraints do. These tradeoffs definitely had an impact on recent evolution, but it appears that the main changes impacting them occurred around the time the apes diverged from the rest of the monkeys, not the time humans diverged from the rest of the chimpanzees.
One thing that I often hear in relation to human brain size is that the upper bound of our brain size is limited by the need for the brain to get through the pelvis during birth.
However, if this were the case, it seems that in equilibrium there should be a number of mutations which increase brain size (and by extension, intelligence), but these variants would be bounded in frequency by their negative effect on maternal survival (and which could provide low hanging fruit for intelligence selection in the modern world since survivability of difficult births is much higher with e.g. blood transfusions and c-sections).
However, as far as I can tell, there aren't genes which have this large effect, and IQ isn't a major predictor of difficult labour (though I haven't searched too much and I've no expertise in the area). Do you know what the error is here?
I find this important because it's part of the question of whether human intelligence rose continuously until we hit a critical point at which civilization exploded into life, or whether we were at some kind of long-term plateau and the core change was just a slow accumulation of physical, intellectual and social technologies until a positive feedback loop could take hold.
I've often heard and read that too, but human brains grow more after birth than brains of other species of primates. The need for the brain to pass through the pelvis at childbirth appears to have reached a tradeoff in pre-human apes causing them to have their babies prematurely; and humans to give birth even more prematurely than chimpanzees.
https://carta.anthropogeny.org/moca/topics/proportion-pre-and-postnatal-brain-growth
The fontanelles also significantly reduce the degree to which human brain size, in particular, rather than birth weight of the infant's whole body is correlated with the severity of childbirth. (Unfused fontanelles at birth are another trait humans share with apes, but not other mammals.)
Given that human brains do most of their growth after birth and the radius required for a brain to pass through the birth canal is somewhat decoupled from brain size in humans; I would guess that other factors like calorie availability have had a bigger impact on limiting adult human brain size than birth constraints do. These tradeoffs definitely had an impact on recent evolution, but it appears that the main changes impacting them occurred around the time the apes diverged from the rest of the monkeys, not the time humans diverged from the rest of the chimpanzees.
Thank you. That's very interesting! - Sidenote: Us being born premature might have been important in selecting for smart moms, I once read - got it: https://www.economist.com/science-and-technology/2016/05/28/of-bairns-and-brains