We seem to be getting swelled heads. Or at least bigger ones.

A study published in the British Dental Journal ran a comparative study between the skulls of modern day people, and two sets of older skulls. They came to some unexpected results: the shape of the human skull has changed considerably in the six or seven hundred years between the modern and medieval samples.

It would appear that our skulls, and most likely our brains, are getting selectively bigger.

Two sets of older skulls, thirty from London plague victims of the mid-14th century and another fifty-two from the wreck of the Mary Rose in 1545, were measured in several different dimensions, including the height of the cranial vault (the measurement from eye to top of head). The old skulls had an average height for the cranial vault of 80mm. These were compared with a set of modern skulls (measurements taken from dental records). The average cranial vault height for the modern skulls? 90mm 95mm⁠⁠—a more than 18% increase.

What exactly the increase in size means is something else again. The first impulse is to attribute it to an increase in intelligence. Certainly Dr. Peter Rock, who led the study, suggests that the increase in size may reflect an increase in mental capacity, but this seems a little premature. Firstly, it falls to a common misconception that brain size directly relates to mental capacity. This has been proven false a number of times. In general across species, mental capacity relates to the brain size relative to body size, not brain size absolute. Within species the given brain size of an individual seems to have no predictable effect on intelligence, with the exception of specific brain diseases that can lead to abnormally large or small brains. Given that the average human has increased in size and height over the centuries, the measured increase may simply be reflective of this larger change, or it may reflect the very different nutritional status of the modern, first-world human, as compared to most of the rest of humanity throughout history.

Nonetheless, the alteration is something that deserves to be looked at more intensively. The increase in cranial vault height is not the only difference that the researchers found between the modern and medieval skulls, merely the most dramatic. Facial features in the medieval skulls were more prominent, which may be the result of dietary changes to softer more processed foods that require less chewing. In an interesting note, a similar set of changes (increased cranial vault height, decreased prominence in the facial features), was noted when a series of Nubian skulls ranging from 12000 BCE to 1500 CE were measured. The changes in both features were attributed to the Nubians’ change in diet to food which required less mastication, and therefore less development in the muscles and bones used to support jaw activity, rather than to an increase in mental capacity. However, while it is easy to see why less developed jaws and jaw musculature would lead to smaller, less prominent faces, it is less easy to see how it would lead to increased cranial capacity.

Many of the questions raised by studies of this kind are not currently answerable. There is no way we can go back in time to administer a battery of intelligence tests to the owners of the medieval skulls. Nonetheless, the questions themselves are intriguing, and as we gather more data, both ancient and modern, we may find more answers than we think – and of course even more intriguing questions.