Ashley Madison founder Noel Biderman makes it clear that he's in the "science-shows-monogamy-is-bunk" camp. In an interview with The Washington Post last year, Biderman cited the book Sex at Dawn (which is, to be fair, an interesting read) and claimed that science was on his side.
"You get married, and after a period of time, your sexual attraction to your partner seems to wane," Biderman said. "Monogamy emerged from an economic principle [ownership]... What we really meant was, women need to be monogamous. I don't think men ever had an intent to be monogamous."
It's unnatural, he insists, and that's why his Web site - which provides a discreet (erm, formerly discreet) outlet for extramarital affairs - is a net positive for the world.
It's true that less than 5 per cent of mammals in the world share life-long monogamous bonds. And humans don't have the same stunning track record as some of those animals.
"I don't think we are a monogamous animal," Pepper Schwartz, a professor of sociology at the University of Washington in Seattle, told LiveScience. "A really monogamous animal is a goose - which never mates again even if its mate is killed."
So it's clear that humans - who date, sleep around, form polyamorous relationships and polygamous marriages and so on - can't be defined as a monogamous species in the same way geese can. But should we be striving towards that goose-y standard? Some scientists think so.
"There are probably good arguments that we're evolutionarily designed to steal from other people, that we're evolutionarily designed to get into physical fights with people that threaten us, that we're evolutionarily designed to walk around naked," Scott Haltzman, a psychiatrist at Fatima Hospital, told The Washington Post.
As far as Haltzman (and many in his field) are concerned, the evolutionary history of human sexuality isn't all that important. At some point, we decided to pair up with one another - and it's a pretty smart reproductive strategy.
Human men have less of an opportunity to sow their wild oats without repercussions, so they may end up with fewer offspring. But they're able to identify a child as their own, based on the monogamy contract they've bought into, and they're able to invest resources in that child - and in its mother - to be sure any offspring produced will make good on dad's genetic contribution.
Monogamy "could be how humans were able to push through a ceiling in terms of brain size," Kit Opie of University College London told the New York Times.
There's also evidence that some polygamy might lead to a more tumultuous society. But that really only seems to be the case when men are marrying multiple women - leaving more unwed men lying around - which of course isn't the only way for a culture to be sexually non-monogamous.
But while the evolutionary benefit is an obvious argument for social monogamy - forming a pair in order to care for a child until it reaches maturity - it doesn't negate the idea that sexual monogamy need not be part of that deal. Plenty of humans pair up socially without practicing life-long sexual exclusivity, and lying and cheating need not be part of such an arrangement.
Like we said - it's complicated.
The current takeaway? We aren't geese, so it's silly to pretend that monogamy is hard-wired into our brains. But it's a bit of a stretch to claim that humans are inherently desperate for sexual freedom. Perhaps the thing that really separates humans from the rest of the animal kingdom is our status as sort-of-monogamous: Some will pair up for life, some will stray, and some will have relationships entirely of their own making.
But even if monogamy isn't in your personal wiring, you probably shouldn't use "science" to justify lying to your spouse.
