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Abbreviated Version

During cold periods and starvation dozens of ape species became extinct because a lack of body fat forced the brain to use muscle as fuel causing weakness after only a few days and death within weeks. One species of upright ape survived this period of starvation during the Plio-Pleistecene due to a dramatic increase in body fat.
Just as critical to survival was preserving muscle and eliminating excess body fat.
"Lean Genes" calibrated these two facets of physiology.


Archive illustration; Source unknown.

Chimpanzee Family Group

Primates all have close, structured families, like humans. But unlike humans, in nature, most primates have little excess body fat.