More evolutionary monkeyshines

Is it ignorance? Early-onset senility? A misinformation campaign secretly funded by fundamentalist religious organizations? Or are most science journalists actually monkeys who have been chained to desks and trained to write blogs, in exchange for food?

You’d think that after 150 years of research and education, people who write about evolution would have acquired a dim understanding of it. On the other hand, you don’t need any qualifications at all to write about anything under the sun these days. I refer to a press tizzy triggered by a recent publication in Nature Communications. The subject was the fascinating field of monkey faces. You can find the paper here.

The paper demonstrates three things, which can be recovered from the abstract, if you take the time to read it:

• Scientists can model the faces of closely related species of primates on the computer.
• An analysis of markings on their faces show that over time, the faces of closely related species of monkeys have become more and more different.
• This could have had an evolutionary function by helping a member of one species identify members of its own species to mate with, which was more liable to produce fertile offspring than mating with members of another species.

What the popular press made of this was quite different. Here are some outtakes:

“The reason we all look different has been revealed by scientists – it is to avoid inter-breeding. Primates were found to have developed different facial appearances so that their group was easily recognizable as being different from closely related and local species.”

And:

“Have you ever wondered why humans don’t all look the same? After all, we share a number of similarities on the inside, but on the outside we all have unique features. The answer, according to scientists at the University of Exeter and New York University, is that some animals developed this was (sic) to deliberately avoid interbreeding.”

Oh my, where to start? First of all, we have a confusion of inbreeding with interbreeding. Both are things you probably want to avoid, but it doesn’t hurt to keep them straight.

Inbreeding refers to mating between very closely related members of the same species – humans have laws against that; it falls under the category incest. The citations above focus on differences between the faces of humans – ergo inbreeding – which this paper tells us nothing at all about. If it did, the findings would imply that your brother or sister ought to look a lot different than you, presumably so that you wouldn’t be attracted to them and choose them as a mate.

The paper’s authors are actually talking about interbreeding between different species. It’s more like an explanation for why we look different from Neanderthals, or gorillas. If at some point humans, gorillas, and Neanderthals ran into each other all the time, maybe they visited the same pubs, you’d need to keep them straight. Otherwise at closing go home with a member of another species.

That might make for an interesting one-night stand, but any offspring produced by these encounters probably wouldn’t be fertile. Hybrids might go on to live long and happy lives, but since they couldn’t reproduce, they wouldn’t pass along their genes. So you’d never know – unless they wrote blogs about their experiences. Maybe they have. I haven’t checked.

Now an even worse mistake, from the point of evolution, is to assume that people, or monkeys, or anything else evolved some feature in order to achieve something. In fact, the opposite is true. A feature already has to be around for natural selection to work on it. If monkey faces look different, and natural selection gets its hands on them, then they might end up looking more different. You can’t actually prove that this is why their faces evolved this way, but at least it’s a plausible story.

The best way to understand this might be by looking at another paper published in Nature, concerning the discovery of variant of a gene called EPAS1 that helps Tibetans live at extremely high altitudes. What didn’t happen was some sort of committee meeting among early inhabitants of Tibet, where they sat around and said, “Hey, we ought to evolve in order to live up there in the high mountains.” Instead, a gene variant evolved that allowed some people to live much more comfortably at high altitudes. So they moved up the hill, got jobs as Sherpas and Yeti-hunters, and left everybody else down at the base camp.

And actually the new paper shows that Tibetans probably acquired this form of EPAS1 by mating with an earlier population of modern humans called Denisovans, who apparently belonged to a different sub-species. I guess they didn’t look different enough; after enough beer, or in the dim lighting of a bar, some interspecies mating took place. In this case the kids were fertile, at least some of them, and they did well at high altitudes. So the best place to find their descendants is a high mountain somewhere. They don’t have to live there, but they can. It would cut down on unwanted visitors and cell phone calls.

But this sort of “secret intentionality” is found all over the place in discussions of evolution – even in articles which are otherwise relatively good. In this one, for example, a writer summarized a new findings about feathers on Archaeopteryx, a dinosaur from the Jurassic period:

“The function of the Archaeopteryx’s feathers, the Jurassic specimen, on their hind limbs has left researchers scratching their heads. Scientists constantly debate about the use of the Archaeopteryx’s feathers, but it seems that finally they are yielding some possible answers.

“Paleontologists from the Ludwig-Maximilians-Universität (LMU) aim to put an end to the dispute with regard to a well preserved specimen. The findings reveal that the first Archaeopteryx feathers were not evolved for flight, but for display.”

Once again, “were not evolved for flight, but for display…” Saying that feathers evolved for something is getting things backwards again. It would be better to write something like: “Feathers evolved in Archaeopteryx before it could fly. Once they appeared, they may first have influenced choices of mates, leading to adaptations in response to sexual selection. Whatever selective pressures acted on feathers, the result was structures that permitted flight. Once Archaeopteryx had that capacity, feathers surely underwent further changes as a result of new selective events.”

Reference:
William L. Allen, Martin Stevens & James P. Higham. Character displacement of Cercopithecini primate visual signals. Nature Communications 5, Article number: 4266 doi:10.1038/ncomms5266.

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