The modern human brain developed much later than scientists believed

The modern human brain developed much later than scientists believed, after the first dispersal of our ancestors from Africa, a new study revealed Thursday.

Thus, the genus Homo, which includes many extinct species (Homo Erectus, Neanderthal man …) and ours (Homo Sapiens), has not always had a similar evolved brain.

The researchers set out to unravel what until now has been a mystery: “When did the brain structures that make us humans change?”, summarizes Christoph Zollikofer, paleoanthropologist at the University of Zurich, Switzerland, and one of the co-authors of the study published Thursday in the prestigious journal Science.

“People thought that the human-like brain evolved at the start of the genus Homo, around 2.5 million years ago,” he explains to AFP.

But this evolution took place much later, 1.7 to 1.5 million years ago., conclude this new work.

To achieve this result, he and his colleague Marcia Ponce de León, lead author of the research, studied numerous skull fossils from Africa, Georgia and Java (Indonesia).

Since brains don’t fossilize, the only way to observe their evolution is to study the marks they have left inside the skull.

So the scientists “scanned” the skulls and created a virtual image of what filled them long ago, like a mold, called an endocast.

What characteristics did you look for to determine the “Modernity” of a brain?

In humans, “some areas of the frontal lobe are much larger than those of great apes»Explains Christoph Zollikofer. One of them is the region of Broca, associated with the language.

This expansion has the effect of pushing everything back. “And this backward movement can be seen in the fossil endocast, when we detect the impressions of the cerebral fissures.”

Thanks to the study of African skulls, The researchers were able to determine that the oldest, dating back more than 1.7 million years, had a frontal lobe characteristic of great apes..

“This first result was a big surprise”, explains the paleoanthropologist. This means that the Homo genus “started with bipedalism (the ability to walk on two feet), not with a modern brain,” he summarizes, and that the evolution of the brain “has nothing to do with being bipedal”.

“From now on, we know that in our long evolutionary history (…), the first representatives of our genus Homo were terrestrial bipeds, with a brain similar to that of the great apes”, he adds.

On another side, Younger African fossils, 1.5 million years old, revealed characteristics of modern human brain.

This means that the evolution took place between these two dates, in Africa, according to the study.

This conclusion is corroborated by the fact that it was at this time that more complex tools appeared, called Achelenses., which have the particularity of having two symmetrical faces.

“It’s no coincidence,” Zollikofer says, “because we know that the areas of the brain that are developing at this time are those that are used for complex manipulations, such as making tools.

Why did this evolution take place? The researchers’ hypothesis is that a virtuous circle has developed between cultural innovations and physical changes in the brain., and who stimulated each other.

The study’s second surprising result comes from observations made on five skull fossils found at the Dmanisi site in present-day Georgia, dating from 1.8 to 1.7 million years ago. The specimens are particularly well preserved. These turned out to have primitive brains.

However, “We believed that large, modern brains were needed to disperse outside Africa”said the paleoanthropologist.

Now “we can show that the brains (of these populations) were neither big nor modern, and yet they came out” of this continent.

Finally, the more recent Javanese fossils had modern characteristics. Therefore, researchers believe there was a second dispersal from Africa.

In short, “there is an initial dispersion of populations with primitive brains, then the modern brain evolves in Africa, and these people disperse again”, as far as Indonesia, explains Christoph Zollikofer.

“This is not a new hypothesis, (…) but for the first time we have fossils which prove it.”

With information from AFP

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