A recent Washington Post headline has people up in arms: “Horns are growing on young people’s skulls. 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. Photo: 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 stabilize 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.

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 basketmaking. 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 WaPo 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.

Figure 4 from Shahar and Sayers (2018) paper. The figure seems to show a high frequency of “extended external occipital protuberance” (EEOP) in young adults, above 40% in females and above 35% in males, with lower frequencies in both sexes above age 30. But this conflicts starkly with the text, which reports that males have the trait more than 5 times as often as females.

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 [enlarged external occipital protuberance] 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 three days ago, long before the WaPo 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.