Humans Have Bigger Brains Than Apes Due To Faster Metabolism

Humans can thank their faster metabolism for their bigger brains compared to other apes. They also have higher levels of body fat, which store energy reserves that fuel the increased metabolic rate, says a new study from Loyola University Chicago.

The study found that when consumption is adjusted to body size, humans consume 400 more calories every day than chimpanzees and bonobos. The daily consumption also totals 635 more calories than gorillas and 820 more calories than orangutans.

The data confirms the team's surmise that the quick metabolism and high energy budget of humans have evolved in order to factor the higher caloric requirement of bigger brains. Faster metabolism is also related to increased offspring and lifespan, which gives a good insight into the adaptation.

Scientists measured the total energy expenditure, including calories burned by metabolism at rest, as well as those fired during intense physical activity among humans and great apes in seven to 10 days.

The scientists studied 141 humans, 27 chimpanzees, eight bonobos, 10 gorillas and 11 orangutans. Gathering information from Modeling the Epidemiological Transition Study (METS), that included adults from the U.S., South Africa, Ghana, Seychelles and Jamaica, the study tried to give an insight into the relationship between physical activity, energy expenditure and weight gain in adults.

The study showed that body fat percentage was higher in humans. Moreover, only humans displayed a gender difference, with 22.9 percent body fat in men and 41.7 percent in women.

As humans and great apes have a close evolutionary history in the hominoid superfamily, the findings seem to be revealing. They could enable scientists to reveal new ways of fighting obesity and metabolic diseases.

"Humans exhibit an evolved predisposition to deposit fat whereas other hominoids remain relatively lean, even in captivity where activity levels are modest," the Loyola University Chicago researchers wrote. "Untangling the evolutionary pressures and physiological mechanisms shaping the diversity of metabolic strategies among living hominoids may aid efforts to promote and repair metabolic health for humans in industrialized populations and apes in captivity."

The findings were published in the May 4 issue of the journal Nature.