Why do we, in the land of the free, have a prohibition of polygyny, a victimless crime? Why does the law restrict people’s freedom needlessly? Why do consenting adults have many legal restrictions to their sexual liberty? Teenage sexuality is full of legal problems (Consult a lawyer before playing doctor. Perverse sex laws traumatize children).  

Why do we feel a compulsion to meddle in other peoples freedom to form whatever form of marriage or sexual relationship they might want to engage in?

Many women would rather be the second (or fifth) wife of an attractive, rich, powerful man like  Tiger Woods or Brad Pitt, then the first  and only wife of boring, fat, jobless, broke alcoholic Joe Bloke in a Detroit ghetto.  Even just being Tiger’s mistress is much more exciting then Joe Bloke. Why does our law restrict the liberty of these women, and of Tiger Woods?

Repression of other people’s sexuality is in the reproductive interest  of older married women, of unattractive men. Even vor the successful alpha male it is advantagous to repress sexuality in others,  while hypocritically pursuing his own promiscuous sexuality (remember Eliot Spitzer?). 

In this post we show that evolutionary theory suggests evolution has created mental modules in our brains to repress sexuality in others,  The gut feelings caused by these modules get rationalized into theories that give rise to repressive legislation.

Polygyny in birds

When good males are scarce, a female bird may prefer to become the second mate of a higher quality male with a bigger territory.

Why Everyone (Else) Is a Hypocrite: Evolution and the Modular Mind by Robert Kurzban $27.95 0691146748 (all quotes are from Kurzban’s book. This book is a must-read to really understand this topic here)

mating pattern of certain bird species illustrates what’s known as the "polygyny threshold model," which has to do with how female birds choose a mate in certain complex environments. [...] Is it better to be the only mate of a poorer male or share a better one? I [a female bird]  can either nest with one of the remaining single – but lower quality- males, or I can nest with a [better high quality] male who is already paired, becoming the second female on his [bigger and better] patch. [...] When the payoff to being the second female on a patch is greater then the payoff to being the only mate of an inferior male, there will be polygyny. (Kurzban, pg. 208)

Morality for the birds?

To better understand how evolution could have formed modules for anti-polygyny morality, Kurzban analyzes a hypothetical bird population where moral rules prohibit polygyny.  He asks

Which birds stand to gain reproductive advantage when polygyny is prohibited?

1. "Clearly, female birds already paired with the best male mates will do better. Their mates won’t be able to acquire secondary females whose offspring would compete for the man’s resources." (Kurzban, p 209). Women married with good males have reasons to be feminists. Hillary Clinton only loses if hubby Bill gets entangled with interns. In contrast, Monica Lewinsky probably would have fared very well as Bill Clinton’s second or even fifth wife.
2. "There’s a natural alliance between monogamously mated females and low quality males because they both gain by enforced monogamy". "low-quality males benefit, since they now might get mates who would otherwise wind up as secondary mates of high-quality males" (Kurzban, p.) In a polygynous animal, primate, or human societies, many low-quality get no wives and no offspring at all. "Low quality males would have a deep, abiding, even crucial interest in rules that force everyone into monogamy" (Kurzban, p 213). Remember, evolution selected for mental modules that gave us reproductive advantage in the EEA, in small groups of hunter-gatherers. It seems that for low quality males, monogamy is the only chance to get a wife, rear  offspring and thus have reproductive success!  Low quality males that successfully prevent the high quality males from monopolizing multiple females would have considerably more offspring then tolerant open minded men who would remain empty handed while the high quality males would get all the females.
3. Almost all males "benefit from all other males being monogamous, even if they themselves are not [monogamous]? [...] "it’s best to constrain others’ sexual behavior. We’re all in favor of moral rule that prevent others from doing things that harm our own interests, but it is to our advantage to not obey our own rule. 
4. High quality alpha males can profit from imposing monogamy  on other males.  Powerful males have a better chance to remain unpunished if they violate these rules (at least in birds with no feminist dominated court system)
5. The losers of polygyny prohibition are un-paired females who have to settle for a lower quality male (‘a loser’)  because they are deprived of the freedom to choose to be wife #2 of a high quality male (with better genes, bigger territory, and more resources). 
6. The other losers  of enforced monogamy are the "cads" the sexy good looking promiscuous players. They are attractive to women for having good genes, but they can’t win the battle over who brings the most worms. "Without promiscuity, sexy males can’t make the most of what they’ve got." (Kurzban, p. 211). 
7. "Dads, however, win if the sexy males can’t be promiscuous. (They also benefit from keeping their females at home, rather than searching for the good-gene cads)"  (p 211) "Dads" are mated male birds that invest in their family and bring home worms for their kids.

We have an "interfere in other people’s private sex life" mental module.

"Humans are extremely social, and our survival and reproduction are determined in large part by how well we navigate the social world. Given this, it’s reasonable to expect that our minds are designed to compete fiercely-if not subtly- for the benefits in the social world: the best mates, the best friends, membership in the best groups, and so on. The outcomes of these competitions would have had massive effects on reproductive success over the course of human evolution."

So birds, mammals, and humans that increase their reproductive success by restricting other people’s sexual access will out-compete the democratic, personal-liberty-respecting tolerant liberal individuals.

We will post more about Kurzban’s theory of the modular mind, and the evolutionary advantages of internal inconsistency, self-deception, hypocrisy to explain this further. But to get a deep understanding one probably needs to read evolutionary literature

• Why Everyone (Else) Is a Hypocrite: Evolution and the Modular Mind by Robert Kurzban $27.95 0691146748 |Amazon paperback or kindle version