Human and Neanderthal brains have a surprising ‘youthful’ quality in common, new research shows

The conversationMany people believe that our particularly large brain is what makes us human – but is there more to it? The shape of the brain, as well as the shapes of its component parts (lobes), can also be important.

The results of a study we published today in Nature Ecology & Evolution show that the way the different parts of the human brain evolved sets us apart from our primate relatives. In a way, our brains never grow up. We share this “Peter Pan syndrome” with only one other primate – the Neanderthals.

Our findings provide insight into what makes us human, but also narrows any distinction between ourselves and our extinct, heavy-browed cousins.

Follows the development of the brain

Mammalian brains have four distinct regions or lobes, each with special functions. The frontal lobe is associated with reasoning and abstract thought, the temporal lobe with preserving memory, the occipital lobe with vision, and the parietal lobe helps integrate sensory input.

cerebral cortex
The four main parts of the brain form the cerebral cortex. Image credit: The Conversation, CC BY-ND

We investigated whether the brain’s lobes evolved independently of each other, or whether evolutionary change in any one lobe appears necessarily linked to changes in others—that is, evidence that the development of lobes is “integrated.”

In particular, we wanted to know how human brains might differ from other primates in this regard.

One way to solve this question is to look at how the different lobes have changed over time among different species, and measure how much shape change in each lobe correlates with shape change in others.

Alternatively, we can measure the extent to which the brain’s lobes are integrated with each other as an animal grows through different stages of its life cycle.

Does a change in shape in one part of the growing brain correlate with change in other parts? This can be informative because evolutionary steps can often be traced back through an animal’s development. A common example is the brief appearance of gill slits in early human embryos, reflecting the fact that we can trace our evolution back to fish.

We used both methods. Our first analysis included 3D brain models of hundreds of living and fossil primates (apes and monkeys, as well as humans and our close fossil relatives). This allowed us to map the development of the brain over time.

Our second digital brain dataset consisted of living monkey species and humans at different stages of growth, allowing us to map the integration of brain parts in different species as they mature. Our brain models were based on CT scans of skulls. By filling the brain cavities digitally, you can get a good approximation of the shape of the brain.

A surprising result

The results of our analyzes surprised us. By tracking change over deep time across dozens of primate species, we found that humans had particularly high levels of brain integration, particularly between the parietal and frontal lobes.

But we also found that we are not unique. Integration between these lobes was also high in Neanderthals.

Looking at changes in shape through growth revealed that in apes, such as the chimpanzee, the integration between the brain’s lobes is comparable to that of humans until they reach adolescence.

At this point, integration rapidly falls away in the apes, but continues well into adulthood in humans.

Comparison of human, neanderthal, chimpanzee, gorilla brain

Left: a diagram showing the degree of integration between the brain’s lobes, with cooler colors indicating higher integration. Right: translucent skulls of a human, Neanderthal, chimpanzee and gorilla, showing the digitally reconstructed brains within. Image credit: Gabriele Sansalone and Marina Melchionna, author stated

Neanderthals were sophisticated people

So what does all this mean? Our result suggests that what sets us apart from other primates is not just our brains bigger. The development of the different parts of our brain is more deeply integrated, and unlike all other living primates, we retain this right into adulthood.

A greater capacity for learning is usually associated with adolescent stages. We suggest that this Peter Pan syndrome played a powerful role in the evolution of human intelligence.

There is another important implication. It is increasingly clear that Neanderthals, long characterized as brutish dullards, were adaptable, skilled and sophisticated people.

Archaeological finds continue to support their development of sophisticated technologies, from the earliest known evidence of string, to the production of tar. Neanderthal cave art shows that they indulged in complex symbolic thought.

Us and them

Our results further blur the lines between us and them. That said, many remain convinced that an innately superior intellectual quality gave us humans a competitive edge, allowing us to drive our “inferior” cousins ​​to extinction.

There are many reasons why one group of people can dominate, or even exterminate, others. Early Western scientists attempted to identify cranial features associated with their own “greater intelligence” to explain the world domination of Europeans. Of course, we now know that the skull shape had nothing to do with it.

We humans may have even come perilously close to extinction 70,000 years ago.

If so, it’s not because we weren’t smart. If we had gone extinct, perhaps the descendants of Neanderthals today would be scratching their heads trying to figure out how their “superior” brains gave them the edge.The conversation

Stephen Wroe, Professor, University of New England; Gabriele Sansalone, PostDoc fellow, Institute of Marine Scienceand Pasquale Raia, professor of paleontology and paleoecology, University of Naples Federico II

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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