Human brains take a lot of energy to run, and keeping our sophisticated grey matter going comes at an evolutionary cost.
Researchers found a trade-off occurs when we have to think fast and work hard at the same time – and our ‘selfish brain’ is always prioritised over the rest of our body.
Our ability to allocate more glucose to the brain could have helped our species survive and thrive by becoming quick thinkers, researchers found.
Researchers found a trade-off occurs when we have to think fast and work hard at the same time – and our ‘selfish brain’ is less affected than our physical capacity (stock image)
Scientists from the University of Cambridge’s PAVE (Phenotypic Adaptability, Variation and Evolution) research group tested 62 male students drawn from the university’s elite rowing crews, with an average age of 21.
Although both our brains and bodies are impaired, findings suggest we have evolved to prioritise quick thinking over fast moving.
‘This enhanced investment in brain size can be considered a defining trait of what it means to be human (along with standing upright on two legs)’, Dr Danny Longman, the study’s lead author, told MailOnline.
‘There is a theory that says that, in our past, humans transitioned from “soldier to diplomat” i.e. from a relatively more muscle dependent to a more brain dependent lifestyle.’
During this time humans began to invest fewer resources in developing and maintaining high levels of muscularity, and instead began to achieve status through the development of enhanced social skills.
‘In this way, humans made the switch to acquiring status through cognitive means, rather than through physical means’, he said.
The rowers performed two separate tasks: one memory, a three minute word recall test; and one physical, a three minute power test on a rowing machine.
They then performed both tasks at once, with individual scores compared to those from previous tests.
As expected, the challenge of rowing and remembering at the same time reduced both physical and mental performance.
However, the research team found that change in recall was significantly less than the change in power output.
Their mental performance fell by 9.7 per cent while their physical performance fell by 12.6 per cent.
Across all participants the drop in physical power was on average 29.8 per cent greater than drop in cognitive function.
Pictured is the lead researcher Danny Longman rowing. The team found rowing and remembering at the same time reduced physical and mental performance
The team say the results of their new study, published today in the journal Scientific Reports, add evidence to the ‘selfish brain’ hypothesis.
This states that the brain has evolved to prioritise its own energy needs over those of peripheral organs, such as skeletal muscle.
‘A well-fuelled brain may have offered us better survival odds than well-fuelled muscles when facing an environmental challenge,’ said Dr Longman.
‘At the evolutionary level, our brains have arguably cost us decreased investment in muscle as well as a shrunken digestive system.’
Human babies also have more stored fat than other mammals, acting as an energy buffer that feeds our high cerebral requirements.
‘On an acute level, we have now demonstrated that when humans simultaneously experience extremes of physical and mental exertion, our internal trade-off preserves cognitive function as the body’s priority’, said Dr Longman.
Dr Longman says a limited supply of blood glucose and oxygen means that, when active, skeletal muscle becomes a ‘powerful competitor’ to the brain.
‘This is the potential mechanism for the fast-acting trade-off in brain and muscle function we see in just a three minute window’, he said.
However, the selfish brain comes at a cost.
‘The selfish nature of the brain has been observed in the unique preservation of brain mass as bodies waste away in people suffering from long-term malnutrition or starvation, as well as in children born with growth restriction.’