Many believe our particularly large brains are what make us human – but is there more to it? The shape of the brain, as well as the shapes of its components (lobes) can also be important.
Results of a study that we published Thursday January 5 in Nature Ecology & Evolution (opens in a new tab) show that the way different parts of the human brain have evolved separates us from our primate relatives. In a sense, our brain never grows. We share this “Peter Pan Syndrome” with only one other primate – Neanderthals.
Our findings provide insight into what makes us human, but also blur any distinction between us and our thick-browed departed cousins.
Follow the evolution of the brain
The mammalian brain has four distinct regions or lobes, each with particular functions. The frontal lobe is associated with reasoning and abstract thinking, the temporal lobe with memory preservation, the occipital lobe with vision, and the parietal lobe helps integrate sensory input.
We investigated whether brain lobes evolve independently of each other, or whether evolutionary change in one lobe appears to be necessarily related to changes in the others – that is, evidence that evolution of the lobes is “integrated”.
In particular, we wanted to know how the human brain might differ from other primates in this respect.
One way to approach this question is to examine how different lobes have changed over time among different species, measuring how much shape change in each lobe correlates with shape change in the others.
Alternatively, we can measure the degree to which the lobes of the brain are integrated with each other as an animal grows through the different stages of its life cycle.
Does a change in shape in one part of the growing brain correlate with a change in other parts? This can be instructive because the stages of evolution can often be traced throughout 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 (monkeys and great apes, as well as humans and our close fossil relatives). This allowed us to map the evolution of the brain over time.
Our other digital brain dataset consisted of living ape and human species at different stages of growth, which allowed us to trace the integration of brain parts in different species as they mature. . Our brain models were based on CT scans of skulls. By digitally filling in the brain cavities, you can get a good approximation of the shape of the brain.
A surprising result
The results of our analyzes surprised us. By tracking changes over time in dozens of primate species, we found that humans have 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.
Examination of shape changes during growth has revealed that in apes, like the chimpanzee, integration between brain lobes is comparable to that of humans until they reach adolescence.
At this point, integration breaks down rapidly in apes, but continues into adulthood in humans.
Neanderthals were sophisticated people
So what does all this mean? Our result suggests that what sets us apart from other primates is not just that our brains are bigger. The evolution of the different parts of our brain is more deeply integrated and, unlike any other living primate, we retain it until adult life.
A greater capacity for learning is generally associated with the stages of youthful life. We suggest that this Peter Pan syndrome played an important role in the evolution of human intelligence.
Read more: When did humans start talking? How language evolved in Africa (opens in a new tab)
There is another important implication. It is increasingly clear that Neanderthals, long referred to as brute beasts, were adaptable, capable and sophisticated people.
Archaeological finds continue to support their development of sophisticated technologies, from the earliest known evidence of twine to the manufacture of tar (opens in a new tab). Neanderthal rock art shows he engaged in complex symbolic thought (opens in a new tab).
us and them
Our results further blur any lines of demarcation between us and them. That said, many remain convinced that some naturally superior intellectual quality has given 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 eradicate the others. Early Western scientists sought to identify cranial features related to their own “greater intelligence” to explain Europeans’ global dominance. Of course, we now know that the shape of the skull has nothing to do with it.
We humans may have come close to extinction ourselves 70,000 years ago (opens in a new tab).
If so, it’s not because we weren’t smart. If we had disappeared, perhaps the descendants of Neanderthals would be scratching their heads today, trying to figure out how their “superior” brain gave them the edge.
Read more: First-ever genetic analysis of a Neanderthal family paints a fascinating picture of a close-knit community (opens in a new tab)
This article is republished from The conversation (opens in a new tab) under Creative Commons license. Read it original article (opens in a new tab).