How Our Big Brains and Flat Faces Evolved in Record Time

By U. College London (UCL), Nov. 3, 2025
https://scitechdaily.com/how-our-big-brains-and-flat-faces-evolved-in-record-time/

Humans’ skulls changed faster than any other ape’s, driven by expanding brains and social forces. 

Credit: Shutterstock

UCL scientists discovered that human skulls evolved far faster than those of other apes.

Using 3D scans, they found that our flatter faces and larger brains developed at roughly twice the expected rate. The results hint that both intelligence and social factors helped drive humanity’s rapid evolutionary leap.

Rapid Evolution of the Human Skull

Humans developed large brains and flatter faces at an exceptionally quick rate compared to other apes, according to new research from UCL scientists. The study suggests that these rapid changes may have offered key evolutionary advantages that shaped the development of our species.

The research, published in Proceedings of the Royal Society B, examined how skull diversity among humans and related apes evolved over millions of years. The analysis revealed that human skulls changed much more rapidly than those of any other closely related ape species, highlighting an unusually fast pace of evolution in our lineage.

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.”

Skull diversity across great apes (orange) and gibbons (blue). Skulls are not to scale. 

Credit: (c) Dr. Aida Gomez-Robles (UCL Anthropology)

3D Virtual Models Reveal Evolutionary Differences

To explore these differences, the researchers created three-dimensional virtual skull models[1] from various modern primates. Their sample included seven hominid species, or “great apes,”[2] such as humans, gorillas and chimpanzees, and nine hylobatid species, or “lesser apes,”[3] such as gibbons.

Hominids and hylobatids diverged from a common ancestor about 20 million years ago. Since then, the two groups have evolved very differently. Hominids have developed a wide range of anatomical diversity, while hylobatids have remained relatively uniform. As a result, gibbon skulls appear strikingly similar across species, whereas the skulls of great apes, particularly humans, are far more distinct. Even within the great apes, humans show the most accelerated evolutionary change.

To quantify this variation, the researchers divided each skull into four major parts: the upper face, lower face, front of the head, and back of the head. Computer analysis of the 3D scans allowed them to calculate how much each region differed among species. This work represents the most detailed comparative study to date of 3D skull structures among closely related apes.

 
Flat Faces and Big Brains: What Sets Humans Apart

Most great apes have big and forwardly projecting faces with relatively small brains, while humans have flatter faces and large round heads. Gibbons, in some ways similar to humans, likewise have relatively flat faces as well and a round head, but a much smaller brain.

The team used the slow evolution and low diversity of hylobatids as a kind of control to compare the variation in hominid skulls. By comparing the species, the researchers found that humans changed about twice as much as would be expected if there wasn’t some additional factor encouraging additional changes.

 
Intelligence or Social Influence?

The researchers cautioned that while it can be tempting to conclude that the evolutionary advantages of greater intelligence from bigger and more complex brains were the primary driver for humans’ rapid evolution, social factors could be affecting these changes as well.

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, orangutan, chimpanzee, and bonobo.
Lesser apes are gibbons, which consist of around 20 different species.

 

 

 

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