We can only make speculative assumptions concerning the structure of human societies long ago. Evidence seems to suggest that gender roles were more firmly established in hunter-gatherer societies than they are presently. We are social predators similar to lions, wolves, and killer whales that hunt in cooperative packs. In other social predators, the females play a leading role in the hunting and killing. In humans, hunting is left primarily to the males because crying babies cannot be brought along.
Human offspring require more care from their mothers than the offspring of any other life form.
Despite the considerable differences in the principal labors of each sex, there was a tacit recognition of the importance of one to the other. An economic and emotional interdependence fostered a greater level of equality than would exist in many more advanced empires that came later. Prehistoric artists painted outlines of their left hands in eighty percent of examples studied, suggesting that the same percentage were right-handed. Some factor changed in culture to skew these ratios. I believe it was literacy.