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Human intelligence has historically been constrained by how big of a head we can push out of human hips, the idea that it's anything like an efficient process has always seemed ludicrous to me.
On the other hand, we know of various mammals with much larger brains that aren't smarter than humans. There are some upper bounds, it seems, on what you can get to in terms of intelligence with the biological substrate humans use.
Its the fact that we have a new substrate with less clear practical limitations that bugs me the most.
We also know of much smaller animals that punch way above their weight class with the tiny brains they have- Birds.
Due to evolutionary pressures after the development of flight, birds have neurons that are significantly smaller and more compact than mammalian ones.
I doubt it's a trivial exercise to just port that over to mammals, but it would suggest that there are superior cognitive architectures in plain sight.
Per this, pigeon brains consume about 18 million glucose molecules per neuron per second.
Human brains consume about 20 watts. Oxidizing 1 mol of glucose yields about 2.8 MJ, so the human brain as a whole consumes about 7.1e-6 mol of glucose per second, which is 4.3e+18 molecules per second. There are 8.6e10 neurons in the human brain, which implies that the human brain consumes about 5 million glucose molecules per neuron per second -- more than 3x more efficient than bird neurons (and more like 10x as efficient as typical mammalian neurons). Which says to me that there was very strong evolutionary pressure for human (and primate in general) neurons to be as small and energy efficient as they could be, and there is probably not a ton of obvious low-hanging fruit in terms of building brains that can compute more within the size, energy, and heat dissipation constraints that human brains operate under.
Of course, GPUs don't operate under the same size, energy and heat dissipation constraints - notably, we can throw orders of magnitude more energy at GPU clusters, nobody needs to pass a GPU cluster through their birth canal, and we can do some pretty crazy and biologically implausible stuff with cooling.
I'm pretty confident you've already read it, but on the off chance that you haven't, Brain Efficiency - Much More Than You Wanted To Know goes into quite a bit more detail.
I have indeed read it, but thank you for the deep dive into the energy expenditures!
It makes sense that mammalian brains are optimizing for low energy expenditure, brains are pound for pound the most expensive tissue to lug around, and space isn't nearly at as much of a premium as in birds.
I think that there's still room for more energy expenditure, the base human brain uses 20 watts, and while I have no firm figures on how much cooling capacity is left in reserve afterwards, I suspect you could ramp it up a significant amount without deleterious effect.
That's just saying that the constraints aren't so tight in the modern environment with abundance of calories, I agree that AIs share very little of said restriction.
5 watts per kg seems to be pretty close to the maximum power output well-trained humans can output for a full hour, so that suggests that a 70 kg human has at least 350 watts of sustained cooling capacity.
Based on sweat production of 2L per hour, that gives an estimate of closer to ~1kW of sustained cooling capacity for an entire human
Bloodflow to the brain is about 45L / h, and brains tolerate temperature ranges of 3-4ºC, so working backwards from that we get that a 160W brain would reach temperatures of about 3ºC higher than arterial blood assuming that arterial bloodflow was the primary heat remover. Probably add in 20-100 watts to account for sweat dissipation on the head. And also the carotid artery is less than a cm in diameter, so bloodflow to the brain could probably be substantially increased if there were evolutionary pressure in that direction.
So yeah, I concur that you could probably squeeze about one more order of magnitude of brain performance out of something roughly human-shaped, if you were not energy constrained (two orders of magnitude would definitely be a stretch for something non-aquatic though).
Thank you for running the numbers again!
I don't think such drastic modification of human cognition will be feasible before an AI singularity shows up, but it's still somewhat reassuring to know that should that not work out, we can still drag our cranial volume kicking and screaming to the power draw of a mid-range GPU haha.
Maybe post your calculations on LessWrong? I don't think anyone has done that particular one before!
Good call
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Ironic that "bird-brained" is considered derogatory.
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