Quanta Discusses Recent Brain Research
Many of you already read Quanta but this is another excellent article that I thought deserved a summary share, How Humans Evolved Supersized Brains. The article delves into the ongoing puzzle as to why and how human brains came to be so big and powerful; why over less than 3 million years they quadrupled in size from 350g to 1,300g, when primates took 60 million years to reach 350g brains in the first place.
Some points of interest:
➤ New techniques to dissolve brains and extract and count cell nuclei give much more accurate cell counts for brains and, for example, show that larger brains do not always have more neurons and neuronal distribution is often different. The human brain has more neurons in the cerebral cortex than any other animal.
➤ While an elephant has a brain 2.5 times as large as a human (2.8kg vs 1.2kg), the cerebral cortex of the human brain has 3 times as many neurons (16.3 billion vs 5.6 billion). This is the first time I’ve come across this fact.
➤ While the human brain as about 86 billion neurons, 69 billion are in the cerebellum and only 16 billion are in the cerebral cortex for high-order intelligence and reasoning. To me this suggests a sort of computational overhang with regard to developing neuromorphic AI: you won’t need hardware that can replicate 86 billion neurons, but only 20% of that – so ~2.5 doublings or ~5 years earlier than expected.
➤ Human brain makes up 2% of body mass but consumes 20% of total energy, whereas a chimpanzee requires only half that.
Analysis of cellular glucose-importing genes in the brain and muscle reveals that such genes are 3.2 times more active in human brains compared to chimp brains, but 1.6 times more active in chimp muscles compared to human muscles, and identically active in the respective livers. Human regulatory sequences for these genes show signs of accelerated evolution. Accounting for size and weight, chimp muscles are about twice as strong as humans.
➤ Key regulatory sequences active in brain development were taken from humans and chimps and introduced into mice: mice with the human version developed brains 12% larger and had cells that divide and multiply in 9 hours instead of 12.
Goldilocks Factors for Human Intelligence
The development of human intelligence appears dependent on a fortuitous confluence of many different factors:
➤ Development of bipedalism to free up hands for tool-making, at the expense of slower movement compared to predators.
➤ Development fire-building and hunting to source easier-to-digest and higher-quality foods due to energy allocation away from gut and muscles.
➤ Development of extreme manual dexterity.
➤ Development of vocal tract capable of complex communication at the expense of choking hazards.
➤ Development of extremely dense and dangerously energy hungry neural cortex at the expense of muscle power.
➤ Development of extreme sociality to facilitate large, stable groups of individuals, requiring a long childhood and retention of play and curiosity with age, at the expense of more than a decade of youthful defenselessness.
➤ I think the general process of neoteny, the retention of juvenile characteristics into adulthood is important here in general to facilitate a great many of these factors.
➤ A complex environment nonetheless conducive to the survival of such a physically weak animal is also important.
When considering the development of intelligence not only on Earth, but also elsewhere in the Universe, these are all important factors that should feed into and influence the Drake Equation and Fermi Paradox. There are a lot of subtle factors that were required to be present in just the right way at just the right time for human intelligence to begin to emerge and develop; a lot of luck seems to have been involved. Primate brains were quite content to remain at 350g for 60 million years, not to mention the dinosaur brains before them that were content to remain smaller for a much longer period of time. I hope as we learn more about these different factors we gain a clearer idea of how astronomically improbable the development of our intelligence was and so a greater degree of confidence that the Great Filter is behind us.
Main article here: https://www.quantamagazine.org/20151110-evolution-of-big-brains/
#brain #intelligence #evolution