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> Evolutionary history points towards brain size being limited by a combination of what is safe for the female hip width and also what amount of energy cost can

• trashtester 2y ago
  > If bigger brains lead to higher intelligence, why do many highly intelligent people have average-sized heads? There IS a correlation between intelligence and brain size (of about 0.3). But the human brain does a lot of things apart from what we measure as "IQ". What shows up in IQ tests tend to be mostly related to variation of the thickness of certain areas of the cortex [1]. The rest of the brain is, however, responsible from a lot of the functions that separates GPT-4 or Tesla's self driving from a human. Those are things we tend to take for granted in healthy humans, or that can show up as talents we don't think of as "intelligence". Also, the variation in the size of human brains is relatively small, so the specifics of how a given brain is organized probably contributes to more of the total variance than absolute size. That being said, a chimp brain is not likely to produce (adult, healthy) human level intelligence. > And do they need to eat much more to fuel their high IQs? That depends on the size of the brain, primarily. Human brains consume significantly more calories than a chimp brains. > If larger brains were always better, wouldn’t female hips have evolved to accommodate them? They did, and significantly so. In particular the part around the birth canal. > I think human IQ might be where it is because extremely high intelligence vs. what we on average have now) often leads to fewer descendants. Less awareness of reality can lead to more "reproductive bliss." I believe this is more of a modern phenomenon, mostly affecting women from the 20th century on. There may have been similar situations at times in the past, too. But generally, over the last several million years, human intelligence has been rising sharply. [1] https://www.sciencedirect.com/science/article/abs/pii/S0306452218304834#:~:text=Stronger%20IQ%20abilities%20are%20associated,beyond%20fronto%2Dparietal%20brain%20regions https://www.sciencedirect.com/science/article/abs/pii/S03064....
  • czl 2y ago
    > There IS a correlation between intelligence and brain size (of about 0.3). Here is a page that shows what such a weak correlation looks like visually: https://resources.nu.edu/statsresources/correlation https://resources.nu.edu/statsresources/correlation It also explains that a correlation of r = 0.3 means only about 9% of the variability in one variable is explained by the other. This makes me wonder: can intelligence really be estimated within 10% accuracy? I doubt it, especially considering how IQ test results can vary even for the same person over time. Kids and teens have smaller brains, but their intelligence increases as they experience more mental stimulation. It’s not brain size that limits them but how their brains develop with use, much like how muscles grow with exercise. > a chimp brain is not likely to produce (adult, healthy) human-level intelligence. > Human brains consume significantly more calories than chimp brains. If brain size and calorie consumption directly drove intelligence, we’d expect whales, with brains five times larger than humans, to be vastly more intelligent. Yet, they aren’t. Whales’ large brains are likely tied to their large bodies, which evolved to cover great distances in water. Brains can large like arms can be large but big arms do not necessarily make you strong -- they may be large due to fat. > But generally, over the last several million years, human intelligence has been rising sharply. Yes, smaller-brained animals are generally less intelligent, but exceptions like whales and crows suggest that intelligence evolves alongside an animal’s ecological niche. Predators often need more intelligence to outsmart their prey, and this arms race likely shaped human intelligence. As humans began living in larger communities, competing and cooperating with each other, intelligence became more important for survival and reproduction. But this has limits. High intelligence can lead to emotional challenges like overthinking, isolation, or an awareness of life’s difficulties. Highly intelligent individuals can also be unpredictable and harder to control, which may not always align with societal or biological goals. As I see it, ecological niche drives intelligence, and factors like brain size follow from that. The relationship is dynamic, with feedback loops as the environment changes.
    • trashtester 2y ago
      > As I see it, ecological niche drives intelligence For this, you're perfectly correct. > It’s not brain size that limits them but how their brains develop with use, much like how muscles grow with exercise. Here, the anser is yes, but like for muscles, biology will create constraints. If you're male, you may be able to bench 200kg, but probably not 500kg unless your biology allows it. > If brain size and calorie consumption directly drove intelligence, we’d expect whales As you wrote later, there are costs to developing large brains. The benefits would not justify the costs, over evolutionary history. > Brains can large like arms can be large but big arms do not necessarily make you strong -- they may be large due to fat. A chimp has large arms. Try wrestling it. > and factors like brain size follow from that Large brains come with a significant metabolic cost. They would only have evolved if they provided a benefit that would outweigh those costs. And in today's world, most mammal tissue is either part of a Homo Sapiens or part of the body of an animal used as livestock by Home Sapens. That's evolutionary "success" for you.