Brain evolution: New study uncovers what sets humans apart from chimpanzees

Have you ever stopped to reflect on the similarities we share with chimpanzees? Don’t you think we have some similar features?

Indeed, you’re right — we share about 98.8 per cent of our DNA with them, making them our closest living relatives. However, despite this near-identical genetic blueprint, chimpanzees have not built civilisations or mastered the technological advancements that humans have achieved.

What, then, is the key difference? Neuroscientists may finally have an answer.

A new study published in the Journal of Neuroscience has taken a fresh look at data from the brains of humans, chimpanzees, and macaques — another well-studied species of primate.

“We were interested in understanding what makes different brains tick. And, for obvious reasons, the human brain was one that we were particularly interested in,” Professor Rogier Mars, co-author of the study, told BBC Science Focus.

According to Mars, most studies comparing human brains to those of other animals tend to focus on factors, such as overall size, the size of specific regions, or the number of neurons. “But our philosophy is that if you truly want to understand what’s happening, you need to examine how the brain is organised,” he stated.

With that approach in mind, Mars and his team set out to investigate. Using publicly available MRI data, similar to the scans used in hospitals, they created “connectivity blueprints” of the brains of the three species. These blueprints essentially map how much different regions of the brain communicate with one another.

One area where the team expected to find differences was the prefrontal cortex, a region linked to complex thought, planning, and decision-making.

Often referred to as the brain’s ‘personality centre’, this area plays a crucial role in regulating emotions and guiding behaviour. At first glance, it seems like the obvious place to search for the essence of what makes us human. Indeed, the study revealed that this area showed more connectivity in humans than in the other species.

“The prefrontal cortex is where researchers tend to look when searching for something uniquely human. But we found differences in many areas, particularly in the temporal cortex, which is just above your ear. These regions appeared to be much more interconnected with the rest of the brain in humans than in any other species,” Mars said.

The temporal cortex plays a key role in processing sensory information, particularly sight, sound and language. Given our highly social and cooperative nature, it’s perhaps no surprise that these areas are more intricately connected in the human brain.

“We’re a very social and collaborative species. So those traits are likely the driving force behind the changes we observe,” Mars explained.

All of this suggests that there isn’t a single defining switch that makes humans, well, human. While some believe that a pivotal evolutionary event propelled us to dominance, the reality is likely more complex.

Like our not-so-distant relatives in the trees, we are the result of gradual, far-reaching evolutionary changes that have shaped us over time.

Or, as Mars put it: “There’s not one big thing that makes us different; it’s a bunch of little things.”

Both species have flat faces, bare skin on their palms and soles, and longer arms than legs. While humans have larger brains, both species possess relatively large brains compared to other mammals, which is associated with higher intelligence and complex cognitive abilities.

They both have the ability to reflect on their own thoughts and mental processes, known as metacognition, which plays a crucial role in problem-solving, decision-making, and understanding one’s own mental state, which is a trait shared by both species. They also share social skills and the capacity for tool use, communication, a wide emotional range, and the ability to engage in moral reasoning.

They can smile and laugh, with evidence showing that facial expressions like these existed in chimpanzees long before humans evolved.