Just How Smart Can We Be? Weighing The Limits Of The Human Brain

The human brain is an incredible machine, but it may have reached the limit of its abilities. Evolution could cause our brains to grow a bit more, though bigger may not necessarily be better.

Human brains are relatively big and particularly dense
Human brains are relatively big and particularly dense
Lucia Sillig

GENEVA – Human beings have bad sight, bad hearing and a bad sense of smell. We're not particularly strong either. So how did we become the planet's dominant species? "It's only because of our brain," says Heinrich Reichert from the biocenter at Basel University. "Other than that we are pretty ill-equipped animals."

Neuroscientists aren't modest. They believe our brain is the best out there. Human brains aren't all that different from the brains of other species. They're just better. "It's the same system, only much more powerful," says Reichert. "It's like comparing a super-computer to a PC."

Proportionally to the size of our bodies, our brains are big. But that in itself isn't necessarily an advantage. Elephants have huge brains. Compared to humans, their neurons are bigger as well. But so are the distances separating those neurons, meaning it takes longer for signals to transmit between them.

"What's striking in the human brain is its density," according to Micah Murray from the center of biomedical imagery at the Lausanne University teaching hospital. "Primates' neurons are more compact than those of rodents, for example. If rodents had as many nerve cells as we do, their brains would weigh about 45 kgs. And if you compare our brain with that of a chimp, it has more folds. That allows a bigger surface of grey matter and gives more possibilities for connections between neurons."

Murray believes that our unmatched ability for abstraction, thought complexity, language and learning skills as well as the capacity to project ourselves in the future -- or in fiction -- is what makes our brains exceptional.

Social creatures

So what made brought about such an evolution? To answer that question, neuroscientists are focusing on the expansion of the frontal lobe, a center of superior cognitive functions that developed among primates in general, and humans in particular.

Several studies suggest that group life played a central role in this development. From caves to social events, maneuvering the subtleties of social life well enough to understand who to stick with and who to run away from is a highly complex skill. It can also turn out to be a matter of life or death. Oxford researchers showed there was a strong link between the sizes of primate groups, the frequency of their interactions and the size of their frontal neocortex.

"This link is even more obvious in monogamous species," adds Pascal Vrticka from Geneva University. "That's probably because monogamy makes interactions even more complicated."

Mutations allowing the skull to expand may also have contributed to the development of the human brain. "One of the hypotheses is that the development of language triggered several other functions, like those linked to reasoning," says Murray.

As good as it gets?

Could the human brain become even better? "We're not sure," says Reichert. "Regarding size, its growth is limited by the size of the woman's pelvis - unless it grows after birth. That's theoretically possible… but the question is whether bigger brains would be more efficient."

Post-birth brain growth could also trigger energy problems. The brain is already the body's most energy-hungry organ. Some experts believe that if it further developed, its consumption would skyrocket, just like a sports car that burns more fuel as its speeds up.

Another possibility is that bigger brains could actually slow down thinking – like in elephants. Neurons would have to shrink in order to become even denser in the brain. But there are limits there as well. Studies by Cambridge university researchers suggest that below a certain size, transmissions are no longer reliable. There is too much "noise."

"Biology is like a do-it-yourself project," says Reichert. "In the case of the human brain, it turned out well." Throughout its evolution it overcame obstacles, took advantage of chance and adapted to certain elements in order to reach what seems to be an optimum capacity. Indeed, to go further may require that we get some outside help.

Read the original article in French

Photo – Liz Henry

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