Latest product of basic evolution program.
A creatures probability of survival is dependent its compatibility to the environment relative to its fellows.
Anyone who survives can breed.
This shows that evolution is an intrinsic property of any system where offspring are different from their parent, and suffer environmental attrition. Life is such a system.
Note that with the population sizes shown, it is more likely that random genetic drift will be stronger than selection. And chimps were not the ancestors of humans et al.