Jay Hanson writes:
>
>   A few million years ago, our ancestor Homo Habilis developed
>a hierarchical social life based on hunting and gathering.
>Habilis males and females shared meat and produce, dividing
>jobs by gender:  child care and gathering to females,
>fighting and hunting to males.  Habilis originated the
>hunter-gatherer lifestyle that was to last for millions
>of years until the invention of settled agriculture.

I don't know why you say their social life hierarchical. In fact, I've heard
anthropologists argue that hunter-gatherer societies were not hierarchical.
Division of labor by gender or age or anything else does not necessitate
hierarchy.