08/04/2010 12:30 pm ET | Updated Nov 17, 2011

Maybe Levi's Just One of Several Fathers?

The latest twist in the Levi/Bristol saga--while possibly untrue and certainly unimportant in the larger scheme of things--offers an opportunity to ponder how our ancestors may have understood the process of getting pregnant. The rumor is that Levi's ex had sex with three different guys the week she probably conceived.

Although most of us assume everyone has always understood that just one roll in the hay can result in a baby, that's far from the case. Anthropologists describe societies where pregnancy is thought to result from ancestral spirits implanting a seed, or a woman stepping over a smoking fire, or in the case of medieval Europe, being ravished by an incubus while sleeping. Even Darwin himself didn't know that a single sperm cell was sufficient to result in pregnancy.

In ancestral societies where almost everyone was having a lot of sex, and most women were either pregnant or breastfeeding (when it was unlikely they'd get pregnant), there was really no reason to link sex with pregnancy.

In our newly-released book, "Sex at Dawn," * we describe the notion of "partible paternity," still common in various pre-agricultural societies in different parts of the world.

In the Amazon, for example, the birds and the bees are different. There, a woman not only can be a little pregnant, most are. Several societies have a novel conception of conception: they believe that a fetus is literally made of accumulated semen.

Anthropologists Stephen Beckerman and Paul Valentine explain, "Pregnancy is viewed as a matter of degree, not clearly distinguished from gestation ... all sexually active women are a little pregnant. Over time ... semen accumulates in the womb, a fetus is formed, further acts of intercourse follow, and additional semen causes the fetus to grow more." Were a woman to stop having sex when her periods stopped, people in these cultures believe the fetus would stop developing.

This understanding of how semen forms a child leads to some mighty interesting conclusions regarding "responsible" sexual behavior. Like mothers everywhere, a woman from these societies is eager to give her child every possible advantage in life. To this end, she'll typically seek out sex with an assortment of men. She'll solicit "contributions" from the best hunters, the best storytellers, the funniest, the kindest, the best-looking, the strongest and so on--in the hopes her child will literally absorb the essence of each.

Then, when the child is born, he or she may have several "fathers" who all believe they contributed some of their essence to the formation of this baby. So maybe Levi is the father of his ex's baby. Or maybe he's just one of several fathers.

* Already a New York Times bestseller, we're thrilled to report.