Christopher Ryan, Ph.D. & Cacilda Jethá, M.D.
This one gets recommended to pretty much everyone I will ever talk to (maybe not grandma). A very insightful exploration of human sexuality and relationships today, starting with our past. Great look into how we mate today, what causes us to stray, the problems with this rather recent construct of monogamy and many other thought provoking areas. One of the most influential historical and scientific reads on the topic, and it's not too heavy. Promise.
http://www.sexatdawn.com/
