The biology of monogamy was a hot topic this week, with two high-profile papers both addressing the evolution of monogamy in mammals. The news stories varied wildly in their conclusions, especially when it came to extending the finding to our own species.
The two papers appeared in PNAS and Science. On Monday, Science announced it was lifting the embargo early on its monogamy paper to coincide PNAS, thus allowing both papers to be incorporated into the same news stories. That left the press a lot more time to report the PNAS paper than the one in Science.
The PNAS study focused only on primates. Researchers used Bayesian statistics to attempt to sort out which conditions led up to the evolution of monogamy, and which followed it. Their conclusion: Monogamy spread in primates because it allowed males to protect offspring from infanticide by rivals.
The Science study included other mammals as well, and used different methods of analysis. That led to a different conclusion: Monogamy followed the spreading out of females over large territories. Under such conditions males might leave more offspring by sticking with one mate rather than running after new ones.
There was plenty of coverage, though the British press, being some hours ahead of their U.S. counterparts, may have had a harder time incorporating the Science paper.
Reporters face the important task of pinning these researchers down on how they defined monogamy. Does it mean mating for life – or can animals qualify as monogamous if they pair bond through a mating season? Are they disqualified if there are some extra-pair copulations, as DNA seems to show happens among “monogamous” bird species?
And of course, where do humans fit in? Were we assumed to be monogamous? Do the conclusions of either study apply to us? And can scientific research really say anything definitive about the mating behavior of a species that includes Anthony Weiner?
At Nature, Josh Howgego covered both studies and explained how the research was done in a comprehensible way. He doesn’t tell us whether humans were included as monogamous animals. He does quote researchers saying the results may not be readily applied to us:
“We’re very cautious about extending our conclusions to humans,” says Clutton-Brock. “Humans are so very unusual because they have culture — and that changes things.”
In this story by Carl Zimmer at the New York Times, humans aren’t addressed at all.
And yet our species was the main focus of attention in other stories, including one by Steve Connor at the Independent headlined: Humans Evolved Monogamous Relationship to Stop Men Killling Rival’s Babies, Study finds.
Here’s the lede: Monogamy evolved in response to the threat of babies being killed by rival men, according to an extensive study of our nearest primate relatives that explains why a marital system based on one man, one woman became the norm for rearing children in many human societies.
The story never supported these strong statements about humanity. And yet, it did have some interesting background on monogamy in other animals. How can any story about monogamy ignore birds, after all? A section at the end explains monogamy among angelfish, swans, and that distinctly British organism known as “Posh n Becks”.
At the Guardian, Ian Sample also leads with humans, but he includes plenty of outside sources who acknowledge the confusion about the definition of monogamy and the variability of human behavior.
Both the Independent and Guardian stories focus on the PNAS paper and not the Science one, which is fair enough since they are hours ahead of us and the sudden embargo change happened for them in the late afternoon.
But so far the news is confusing from both sides of the pond. Are the researches on either study assuming humans are monogamous? If our monogamy evolved independently, how can we be sure it was driven by the same selective pressures that acted on other primates?
I got some answers from AP, NPR and Science.
In his story for AP, Seth Borenstein explained whether the researchers in either study included humans and how we were classified. I couldn't find as clear an explanation ot this basic question in any of the other stories:
The studies are published online Monday in the journals Science and the Proceedings of the National Academy of Sciences. The mammal paper in Science excluded humans while the primate analysis in PNAS counted people both as monogamous and not, because that differs around the world.
Michael Balter also offered some helpful insight into the human condition in his news story for Science. His sources tell him that the data can’t be extended to humans because we’re not completely monogamous.
Richard Harris at NPR also found his sources urged caution about applying the results to humanity. His version of the story showed how to make the science gripping in its own right, without having to artifically stretch the implications for humans.
In the end, a couple of gaping questions remained unanswered. Why should there be single evolutionary pressure driving the selection of monogamy if it evolved independently in different lineages, especially our own? If monogamy evolved in some of our fellow primates because it protected against infanticide, why would this necessarily apply to the completely separate evolution of monogamy – or partial monogamy – in humans? What about the spread-out territories? How could that apply to social animals like us?
Another gap: I couldn’t find any stories that addressed the frequency of infanticide. How do scientists know which species do it and how often they do it? How good are the data going into the PNAS paper’s algorithm?
The papers both discuss monogamy as a mating strategy for males, but why? After all, it takes two to form a pair bond or a quick hookup. There is a good reason, of course, in that the sexes face different selective pressures. For general readers this must be explained, however, to avoid further confusion.
And most reporters never clarified the working definition of monogamy as it applied to this research. How much serial monogamy or extra pair copulation is allowed among “monogamous” animals? The only story that addressed it in any detail was Michael Balter’s in Science, and there he found that biologists, like the rest of us, remain somewhat confused.
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