According to a new study, guys stopped sleeping around and settled down in respectable families once their friends starting killing their kids.
Okay, that's not actually what it said. The study, published in Proceedings of the National Academy of Sciences (PNAS), was a study that correlated various traits in primates with the emergence of monogamy to better understand how it might have evolved. Their data showed that monogamy correlates better with infanticide than with any other behaviour that had been hypothesized to lead to monogamy. Infanticide is presumed to be an offensive strategy; a male in a given group increases the chance of his own offspring surviving by killing off other young. So they conclude that monogamy evolved as a defence mechanism against infanticide.
Another study, published in Science, disagrees. They see monogamy arising from females spreading out and becoming more territorial, reducing the benefit gained from a male moving from female to female, and hence enhancing the relative benefit gained from sticking with one woman.
One point that both studies make, though, is that their results are for non-human mammals. It's an open question as to whether humans are "naturally" monogamous, or even whether the question is one that can have an answer, given the dominant role that culture plays in human sexual and child-raising arrangements, and given that just about every type of arrangement has been observed in various human cultures through the ages.
Which is why it's curious that many news reports on this story start out with a hook along the lines of, "Why are humans monogamous?" The summary of the research on the Science news site even includes a picture of Will, Kate, and royal baby at the top of the article, subtly suggesting that perhaps the pomp and pageantry of a British royal wedding all springs from His Royal Highness' instinctual desire to keep the Duke of Somerset from killing wee Prince George1.
It's an inaccuracy, to be sure, but on the whole it's forgiveable; the research does relate, even if it's more tangential than the headlines would imply. (As an aside, it's interesting that the report in the CBC, a government funded agency that hence isn't as reliant on page-views for revenue, is much more cautious--and accurate--than the reports from profit-driven private media companies.)
The bigger problem is one that plagues almost every story about evolutionary research. We can't seem to get away from the language of choices (and hence morality) when talking about animal behavioural strategies. As an example, CNN summarizes the infanticide driven pairing by noting that, "a male that lives with a female mate can protect their offspring from other males, that might want to kill these children." The author is trying to be neutral, but it's hard to see phrases like "protect their offspring" and "want to kill these children" without overlaying human notions of choice and morality on them.
To get away from this, it's important to note that evolution in the genetic sense has nothing to do with choice. Evolution acts on behaviours that are hard-coded into genes, because ultimately it's the genes that evolve, not individuals.
As an example, let's consider a set of identical, early human twins. One of our primordial twins, whom we'll call the Fonz, doesn't let anyone tie him down. He has a girl in every cave, an no idea of how many kids he may have fathered, let alone their names. The other, whom we'll call Ward, is a devoted father, marrying his cave-sweethard and dedicating himself to raising his little cave-children. Now we could argue about which strategy was more successful: perhaps the Fonz's promiscuous strategy will pay off and he'll have dozens of children that go on to have children of their own. Or perhaps he'll have more kids but, without a father, they won't do well and Ward's six well-raised children will ultimately out-breed them. Since we started with the assumption that they're twins, though, none of this matters. They carry the same genes, so there can't be any selective reproductive success, which is the driver of evolution. As soon as individuals can choose one strategy or another, all bets are off. Evolution does not select between strategies that individuals choose.
This is, of course, getting into deep philosophical waters. How much choice do any of us actually have, and how much is determined by genetics? It's not a debate I really want to get into here. The point is that evolution only acts on behaviours that are determined by genes; in that sense, it's incompatible with choice. If we want the public to understand evolutionary science, then, we need to come up with a new vocabulary. One that doesn't rely on words that imply thought out strategies, or foresight, or choice. How do we do that? I don't know, but if we take science communication seriously it's worth the effort to try.
1I am in no way suggesting that the Duke of Somerset actually wants to kill wee Prince George. I'm sure the Duke has no baby-killing tendencies whatsoever and is a very nice person, even though he has a huge amount of money and power for no better reason than that his great-great-...-great-great-grandmother was the only one of Henry VIII's wives to die before he got tired of her.