EQ is NOT the whole story. As I just noted above in another comment, there is amazing work on brain architecture coming out of the lab of Dr. Suzana Herculano-Houzel, a scientist studying neural structure across the vertebrates. I recommend her book, “The Human Advantage” and all the papers to have come out of her lab recently.
Three important things:
1 - Neural scaling laws differ from clade to clade. In a generic mammal, a brain 10x as large has only 4x as many neurons so there is diminishing returns to brain mass probably due to the need to maintain long connecting fibers. Primates break this relationship—all primate brains are roughly equally densely packed, and indeed are as densely packed as a generic mammal brain from a very small mammal. Something changed in primate embryonic development upwards of 50 megayears ago predisposing large primates to have much larger numbers of neurons (Practical example: turns out the cerebrum of an elephant is roughly equivalent to that of a chimp and the largest whales probably correspond to early homo erectus).
2 - Humans are actually incredibly generic primates. All of the pieces of our brains fall right on the primate trend lines in terms of size and cell number—our cerebrum is not oversized, its just that the cerebrum grows faster than other parts with increasing brain size across all the primates. We just happen to have the largest neuron number. And also, humans fall right on the body size to encephalization quotient trendline of all the primates, with only 3 primates falling off the trendline—chimps, gorillas, and orangutans are below the trendline with brains much smaller than you’d expect for their body sizes. She hypothesizes, for very sound reasons explored in their papers and her book, that this was due to energy constraints because brain tissue is energetically expensive, and that humans were able to get back onto the generic primate trendline and have brains as big as you’d expect for a primate of our body mass once we started cooking and could support the energy requirements of brain tissue.
3 - Birds are another clade that breaks the usual brain scaling laws. Their neurons do not get bigger with increasing brain size, much like primates, except that their neurons are ~6x as small as primate neurons. Thus, it turns out that corvids and parrots are packing brains equivalent to many monkeys that their EQ would never suggest.
EQ is NOT the whole story. As I just noted above in another comment, there is amazing work on brain architecture coming out of the lab of Dr. Suzana Herculano-Houzel, a scientist studying neural structure across the vertebrates. I recommend her book, “The Human Advantage” and all the papers to have come out of her lab recently.
Three important things:
1 - Neural scaling laws differ from clade to clade. In a generic mammal, a brain 10x as large has only 4x as many neurons so there is diminishing returns to brain mass probably due to the need to maintain long connecting fibers. Primates break this relationship—all primate brains are roughly equally densely packed, and indeed are as densely packed as a generic mammal brain from a very small mammal. Something changed in primate embryonic development upwards of 50 megayears ago predisposing large primates to have much larger numbers of neurons (Practical example: turns out the cerebrum of an elephant is roughly equivalent to that of a chimp and the largest whales probably correspond to early homo erectus).
2 - Humans are actually incredibly generic primates. All of the pieces of our brains fall right on the primate trend lines in terms of size and cell number—our cerebrum is not oversized, its just that the cerebrum grows faster than other parts with increasing brain size across all the primates. We just happen to have the largest neuron number. And also, humans fall right on the body size to encephalization quotient trendline of all the primates, with only 3 primates falling off the trendline—chimps, gorillas, and orangutans are below the trendline with brains much smaller than you’d expect for their body sizes. She hypothesizes, for very sound reasons explored in their papers and her book, that this was due to energy constraints because brain tissue is energetically expensive, and that humans were able to get back onto the generic primate trendline and have brains as big as you’d expect for a primate of our body mass once we started cooking and could support the energy requirements of brain tissue.
3 - Birds are another clade that breaks the usual brain scaling laws. Their neurons do not get bigger with increasing brain size, much like primates, except that their neurons are ~6x as small as primate neurons. Thus, it turns out that corvids and parrots are packing brains equivalent to many monkeys that their EQ would never suggest.