No matter how old and experienced we get, sex and romance never fail to surprise and perplex us. Three new books explore the origins of human sexuality, whether we are capable of monogamy, and why we kiss.

Husband and wife Christopher Ryan and Cacilda Jeth travel back in evolutionary time in Sex at Dawn: The Prehistoric Origins of Modern Sexuality (HarperCollins, 2010) to reveal that modern humans evolved from hunter-gatherers who lived in intimate groups and shared everything—food, chores and even sexual partners. Thus, Ryan, a psychologist, and Jeth, a psychiatrist, argue that we are hardwired to seek multiple partners and that these natural promiscuous urges may explain why half of marriages in the U.S. end in divorce.

Monogamy is not necessarily a natural state for humans, agrees clinical psychologist Marianne Brandon in Monogamy: The Untold Story (Praeger, 2010). Brandon thinks modern society creates unrealistic gender roles—for instance, an ideal man needs to be both sensitive and powerful—and these roles encourage both men and women to repress their sexual instincts. But the key to successful monogamy, Brandon argues, is to use those primal impulses to stoke the flames of desire with your committed partner.

In The Science of Kissing: What Our Lips Are Telling Us (Grand Central Publishing, 2011), biologist and science journalist Sheril Kirshenbaum explores all aspects of a lip lock. For instance, women usually require a kiss to feel intimate with another person, whereas men are more willing to forgo the first kiss and go straight for sex. Although scientists don’t know why we kiss, Kirshenbaum explores several possibilities, such as that kissing rekindles the intimacy we first experienced in infancy when breastfeeding.