Brain body size evolution

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.
Ron Okimoto