John Hawks

A paleoanthropologist researches the whole “millennials are growing horns” headline

PBS

After recent research put forward the idea that millennials are growing horns on their skulls, I thought it best to add some reality to the situation.

 

 

A recent Washington Post piece blew some people’s minds (who then shook their fist at the nearest millennial): “‘Horns’ are growing on young people’s skulls,” it said. “Phone use is to blame, research suggests.” As a professional paleoanthropologist, I’m here to throw some cold water on that claim. The research doesn’t back it up.

The story is about a well-known anatomical feature called the external occipital protuberance. This common trait can often be felt as a bump on the back of the skull, at the middle, just above where the neck muscles attach. Men have it more often than women, so much so that this is one of several traits that help forensic scientists establish whether a skeleton belonged to a male or female individual.

 

An example of an external occipital protuberance on a Bronze Age skull. (Image: John Hawks)

 

What does this have to do with “horns”? Horns are made of keratin, the same stuff as fingernails. There actually are conditions called keratoses in which fibrous growths of keratin emerge from the skin, including on the face and head. But this story isn’t about horns at all. Instead, the story is about a much more common developmental occurrence: the growth of a small spur of bone from the external occipital protuberance (EOP). The idea is that kids are looking down at their cellphones, causing strain on the back of their skulls, which develop into a bone spur as a result. According to the story, upwards of 40% of young men may have such “extended” external occipital protuberances, a much higher proportion than found in men over 30.

But the research doesn’t hold up.

Many features of the skull develop when adolescents are becoming sexually mature, and the external occipital protuberance is no exception. Such traits that differ between men and women are mostly correlated with the size and muscular development of the head. Bone is living tissue, and it gradually responds to the forces of muscles that attach to it. Bone also responds to hormones, and the relationships between hormones, exercise and everyday activity are complicated.

When anthropologists see a variation in traits like the external occipital protuberance, one thing they consider is the mechanical effect of forces on the bone. In the case of the EOP, the main influence is the nuchal ligament, which runs up the middle of the spine. The ligament helps to stabilise your head when you run, and that makes humans different from chimpanzees and gorillas, which don’t have the same neck anatomy for running. Anthropologists also have to think about the general effects of hormones and activity—people vary in the responses of bone to physical forces based on their overall activity level, fitness and health.

Could a trait like the external occipital protuberance result from posture, as young people look down at their cellphones and other devices? On the surface, it seems plausible. In the past, anthropologists have looked at the development of the external occipital protuberance and other features of the skull related to neck muscles, showing many differences between populations. Some past populations with very strenuous activities involving the back and neck have a high incidence of large EOP or other skull developments related to neck muscle attachments.

I’m skeptical that many less extreme examples are “spurs” or “enlarged” EOP at all. What the authors are looking at might have nothing to do with what an anthropologist can see on a bone at all. It might be an illusion.

So far, research into the skulls of past populations hasn’t pointed to a large role for posture, as might result from repetitive activities like weaving and basket making. Most of the literature on the development of EOP and other traits of the occipital bone have focused on more strenuous activities like the use of a tumpline.

What about today? Could cellphones somehow make the difference?

The research study that underlies the Washington Post report came out last year in the academic journal Scientific Reports, published by the Nature Publishing Group. Although it publishes a high volume of papers, the journal is not a joke—I’ve even served as a peer referee on there (not on this paper). That’s one reason why I was so disappointed to see that some serious problems seem to have slipped through the scientific review of this paper. The paper is open access, and anyone can check it out for themselves.

The authors of the study are David Shahar and Mark G L Sayers, from the University of the Sunshine Coast, in Australia. For this work, they collected X-ray images taken of people from the side, showing the curvature of their necks and the back of their skull. These radiographs were collected for other reasons—although the study doesn’t go into details about this, it’s not unusual for hospitals to allow research on X-ray archives after identifying details have been stripped out of the files.

Unfortunately, this study doesn’t hold water. The paper has no table of results, so we cannot see the frequencies that the authors observed. The paper does have one figure (I’ve included it here) that seems to show a difference between people of different ages. But that figure has to be wrong because it conflicts with the text in a major way. According to the text, males are “5.48 times more likely to have EEOP than females (P < 0.001).” That seems like a plausible number—the EOP itself is much more common in males than females. But the figure shows both sexes having very high and similar frequencies.

(Kyle Sheldrick deserves credit for pointing out this error in a comment following the paper last Tuesday, long before the Washington Post story.)

Can we dig into this further? The same authors looked only at young adults in a 2016 study that may have looked at many of the same radiographs as in their 2018 paper. In that earlier study, the authors report frequencies in young men of 67% and in young women of 20%. Those are pretty different values than their 2018 results. They also report different values in university students versus non-university students. And they give some example radiographs.

 

Figure 2 from Shahar and Sayers (2016) showing the method for measuring “extended external occipital protuberance”.

 

I have to say, from that figure it seems to me that the definition of “enlarged” EOP, which the study defined as 5 millimetres as measured above has to include many cases in which there is no notable “extension” beyond the bone surface at all. The two illustrated here are among the most extreme examples—more than four times the threshold—and they are measured in different ways. I’m sceptical that many less extreme examples are “spurs” or “enlarged” EOP at all. They are more likely side views of the thickened area of the superior nuchal line. Altogether, this means that what the authors are looking at might have nothing to do with what an anthropologist can see on a bone at all. It might be an illusion.

There has been more and more interest in looking at larger samples of normal human variation to understand how modern environments are changing people. There’s some really great science happening in this area, as researchers find that previously obscure traits actually may be changing as people’s activity pattern changes. But that research isn’t easy to do—it takes a lot of experience with both dry bone and radiographs to make relevant comparisons. There is a deep history to understanding human bone variation, and the best studies tie that history to new, big datasets.

This skull horn study simply doesn’t measure up. The basic data do not convince me that anything is being measured consistently. And the 2018 paper, which gave rise to the Washington Post story, has such a major error that Scientific Reports clearly should never have published it. Maybe this trait really is changing in Australia. It would be really cool if it’s true. But these studies don’t show that.

Why are people so fascinated by this crazy story? What made it go viral?

For many who are clicking and sharing, the idea of hidden effects from phones just reinforces a moral panic over screen time. Depending on who you ask, young people’s use of cellphones is creating a generation of deviantskilling the art of conversation, and leading to addiction.

As I saw this story crossing my feed, shared by professional anthropologists and non-experts, retweeted by mainstream journalists, I had a sinking feeling. The details of the scientific work simply don’t support the story. Horns growing on young people’s skulls? It’s a juicy headline, but it’s not the truth.

 

 

 

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