Humans evolved faster than any other ape

Humans developed large brains and flatter faces at an unexpectedly swift pace compared to other apes, according to a new analysis of ape skulls by researchers at UCL. The findings suggest that these features may have offered evolutionary benefits that favored rapid change.

The study, published in Proceedings of the Royal Society B, explored how skull diversity evolved among humans and related apes over millions of years. The team discovered that the human skull changed much more quickly than that of any other closely related species.

Lead author Dr. Aida Gomez-Robles (UCL Anthropology) explained: "Of all the ape species, humans have evolved the fastest. This likely speaks to how crucial skull adaptations associated with having a big brain and small faces are for humans that they evolved at such a fast rate. These adaptations can be related to the cognitive advantages of having a big brain, but there could be social factors influencing our evolution as well."

3D Scans Reveal Evolutionary Differences Among Apes

To investigate, the researchers created detailed three-dimensional digital models of skulls* from a range of modern primates. These included seven hominid species, or "great apes,"** such as humans, gorillas and chimpanzees, and nine hylobatid species, or "lesser apes,"*** such as gibbons.

Hominids and hylobatids diverged from a common ancestor around 20 million years ago. Since that split, hominids have developed far greater anatomical variety, while hylobatids have remained remarkably uniform. As a result, gibbons' skulls look strikingly similar across species, whereas the skulls of great apes, particularly humans, show much more diversity. Even within the hominid group, human skulls evolved at a distinctly faster rate than those of other species.

To quantify these differences, the team divided each skull into four main regions: the upper face, the lower face, the front of the head, and the back of the head. They then used computer analysis to compare the 3D scans, measuring how much each section varied between species. This approach provided one of the most detailed comparative studies ever conducted on skull structure among closely related apes.

Most great apes have large, forward-projecting faces and relatively small brains. Humans, by contrast, possess rounder heads and much flatter faces. Gibbons share some facial similarities with humans, such as a relatively flat face and round skull, but their brains are far smaller.

Humans Changed Faster Than Expected

The researchers treated the slow, limited evolutionary change in hylobatids as a kind of control to measure variation among great apes. When they compared the groups, they found that the human skull had changed roughly twice as much as expected under normal evolutionary rates, implying that extra forces were accelerating human evolution.

However, they cautioned against attributing this speed solely to intelligence. While a larger, more complex brain likely played an important role, social pressures may also have contributed.

Dr. Gomez-Robles added: "After humans, gorillas have the second fastest evolutionary rate of their skulls, but their brains are relatively small compared to other great apes. In their case, it's likely that the changes were driven by social selection where larger cranial crests on the top of their skulls are associated with higher social status. It's possible that some similar, uniquely human social selection may have occurred in humans as well."

Notes

* These are virtual representation of actual skulls, obtained from CT-scans of the skulls.

**Great apes are humans and species of gorilla, orangutans, chimpanzees and bonobos.

***Lesser apes are gibbons, which consist of around 20 different species.