Re: Brain body size evolution

On 16/07/2024 13:40, RonO wrote:

https://www.sciencedaily.com/releases/2024/07/240708101004.htm
 https://www.nature.com/articles/s41559-024-02451-3
 The Nature article is open access.
 The authors claim that they have developed a model for the relationship between brain and body weight for mammals and the evolutionary trajectory for different lineages.  With this model they can identify lineages that do not conform to the usual brain size evolution relationship to body weight.  As pretty much every other study has indicated humans have evolved bigger brains for their body weight and primates have a higher rate of brain size increase.  Some lineages have lower brain size to body weight than expected.  As you might expect these are the largest mammals.  They speculate that brains take a lot of energy to maintain, and that there is likely selection against larger brains at some point in body size increase.  Population sizes for large mammals have to be smaller because it takes more food to maintain individuals.  The estimate that I have seen is that it takes 80% of our energy production to run our brains.  If you have smaller brains you could maintain larger populations.  Hunter gatherer populations were probably restricted by our brain's energy needs.  With the poorer agricultural diet our brains actually decreased in size as our population increased.  We could maintain much larger populations on the same amount of territory, but it wasn't a diet amenable to supporting large brains.

The number floating around the web is that the brain (2% of body mass) consumes 20% of resting energy usage (and presumably a lower proportion when performing hard physical labour).
Elsewhere I find it said that the heart and kidneys use more energy per gram than the brain, and the liver and spleen combined use more energy that the brain does.

 Ron Okimoto
 

--
alias Ernest Major