Although the article is about human sexuality, there are some interesting points on the benefits of egalitarianism.

http://www.cnn.com/2010/OPINION/07/27/ryan.promiscuity.normal/index.html?iref=NS1

Seismic cultural shifts about 10,000 years ago rendered the true story of human sexuality so subversive and threatening that for centuries, it has been silenced by religious authorities, pathologized by physicians, studiously ignored by scientists and covered up by moralizing therapists.