Genetic diversity predisposes some individuals to gain fat more easily than others.

“again back to the normal distribution curve right that applies to every aspect of human physiology it also it it applies to our propensity to fat as our our friend Gary taubs would say some people fat much easier than other people and that that's not well you know in modern society that's considered uniformly bad but when you look at the the entirety of our 300 000 years as homo sapien sapien for the vast majority 99 of the time your ability to fatten that was a very very good thing”