Behavioral Ecology Blog

The great human monogamy debate continues to be one of my favorite subjects to write about- which is good, as there is always new stuff coming out to support my hypothesis.

For those of you new to it: the issue is human monogamy. Now the church, your high school sex ed. teacher, and various other “righty” groups would like you to believe that human sexual behavior falls within the realm of monogamy. Let’s just get this straight- it does not. Human sexual behavior typically falls near polygyny on the continuum of possible sexual strategies. Of course, there are monogamous people, but this is not the rule, and is certainly not the biologically driven outcome- but instead is highly influenced by culture. To get around this issue of human culture, indigenous populations are sometimes studies. But before I get into the current study, a review of the evidence is in order.

1. In a 2006 study in Europe, human EPC’s are estimated to be between <1%-30%>
2. EPC to be greater than 20% in Great Britain. (Mid 1990’s study)
3. The teenager promiscuity study.
4. Anecdotal evidence. How many of us:

a. Have never had a friend who cheated?

b. Cheated ourselves?

c. Know somebody who was actually cuckolded?

I know that I have friends that have cheated, and been cheated on. Is my experience unique? I think not. We all know people that have been cheated on, or have cheated. This mass of cheaters adds up to something….

5. Evidence from Adaptation and physiology

a. Sperm competition

b. Adaptive sperm allocation

Now without getting into a Spandrels type problem, the fact that sperm competition theory predicts human sexual behavior and morphology so well strongly suggests that sperm competition has been, and continues to be relevant in human behavior.

OK, so the new study was published online at the Proceeding of the Royal Society B on April 24^th, and details work from the Tsimane form Bolivia. Their goals were to test 2 different hypotheses of why human marriage exists, the provisioning model vs. the mating effort model.

Definitions:

> Provisioning model- males marry and stay because the aid they provide in provisioning enhances reproductive success. If this model is the winner, then males might have EPC’s when the marginal value of parental investment is low- or when there aren’t many offspring to invest in…

> The mating effort model suggests that males marry to monopolize female reproduction. If this is the relevant model, men should stray when fecundity loss is at its lowest- say during pregnancy or directly after childbirth.

So here is the money graph.. It basically shows that infidelity is at it’s highest early on in the relationship- when there are few children to invest in AND late on- when the woman is old and therefore has little residual fecundity. Sorry ladies, that’s just how it is..

So to recap- yet another example of Human non-monogamy. Seems like the consensus (and exactly what is expected), it that makes are more likey to cheat when their partners are infertile, and/or when parental investment is not important.

On an aside, I hope I’m not threatened with legal action as was Shelly Batts by Wiley Publishing. I believe fair use covers us here. Anyway- for some intersting discussion:

Wiley Publishing sucks, fair use, Wiley Publishing sucks, fair use, Wiley Publishing sucks, fair use, Wiley Publishing sucks, fair use.