How human brains become so big
PARIS: The human brain is disproportionately large. And while abundant grey matter confers certain intellectual advantages, sustaining a big brain is costly — consuming a fifth of energy in the human body.
It is an oddity that has long flummoxed scientists: while most organisms thrive with small brains, or none at all, the human species opted to sacrifice a degree of body growth for more cerebral capacity.
From our ape-like Australopithecus ancestors to modern Homo sapiens, the human brain had tripled in size.
On Wednesday, researchers said they could finally reveal how and why this happened.
The human brain, they suggested, expanded in response to environmental stresses that forced our species to come up with innovative solutions for food and shelter, and pass the lessons on to our offspring.
The finding challenges a popular theory that the thinking organ grew as social interactions between humans became complex, a research duo wrote in the journal Nature.
In fact, the inverse might be true.
“The findings are intriguing because they suggest that some aspects of social complexity are more likely to be consequences rather than causes of our large brain size,” said paper co-author Mauricio Gonzalez-Forero of St Andrews University in Scotland.
“The large human brain is more likely to stem from ecological problem-solving and cumulative culture than it is from social manoeuvring.”
With colleague Andy Gardner, Gonzalez-Forero developed a mathematical model to measure whether being confronted with ecological and social problems has a measurable impact on brain growth, and if yes, how much.
Model “brains” were presented with ecological challenges — finding prey in bad weather or in tough terrain, for example, preserving food to protect it against mold or heat spoilage, or storing water amid drought.
Social challenges were introduced too, to test the influence on brain growth of cooperation and competition between individuals and groups.
Interestingly, cooperation was associated with a decrease in brain size, the researchers said — probably because it allowed individuals to rely on each other’s resources and to save energy by growing smaller brains themselves.