From the Guardian: “Study shows that modern hunter-gatherer tribes operate on egalitarian basis, suggesting inequality was an aberration that came with the advent of agriculture.”
Read more here: http://www.theguardian.com/science/2015/may/14/early-men-women-equal-scientists
Feminist Philosophers 
Several feminist historians such as Gerda Lerner and Riane Eisler have suggested this for many years.
Also, Beauvoir in _The Second Sex_. :-)
Reblogged this on A Feminist ReadMe.
Or if Engels was right, not just agriculture but agriculture plus private property and resource accumulation.