Why do men talk and women gossip, and which is better for you? Why is monogamy a drain on the brain? And why should you be suspicious of someone who has more than 150 friends on Facebook?

We are the product of our evolutionary history, and this history colors our everyday lives—from why we joke to the depth of our religious beliefs. In How Many Friends Does One Person Need? Robin Dunbaruses groundbreaking experiments that have forever changed the way evolutionary biologists explain how the distant past underpins our current ­behavior.

We know so much more now than Darwin ever did, but the core of modern evolutionary theory lies firmly in Darwin’s elegantly simple idea: organisms behave in ways that enhance the frequency with which genes are passed on to future generations. This idea is at the heart of Dunbar’s book, which seeks to explain why humans behave as they do. Stimulating, provocative, and immensely enjoyable, his book invites you to explore the number of friends you have, whether you have your father’s brain or your mother’s, whether morning sickness might actually be good for you, why Barack Obama’s 2008 victory was a foregone conclusion, what Gaelic has to do with frankincense, and why we laugh. In the process, Dunbar examines the role of religion in human evolution, the fact that most of us have unexpectedly famous ancestors, and why men and women never seem able to see eye to eye on color.