A new study from Loyola University Chicago researchers has revealed that humans were able to evolve bigger brains than other apes due to a faster metabolism. In addition, the study found that humans also have higher levels of body fat, which stores energy reserves that are, in turn, used as fuel to sustain the increased metabolic rate.
When adjusted for body size, humans consume 400 more calories on a daily basis than chimpanzees and bonobos, 635 more calories than gorillas and 820 more calories than orangutans.
The data confirms the team's hypothesis that the faster metabolism and higher energy budget of humans evolved in order to accommodate for the higher caloric requirement of larger brains. Furthermore, faster metabolism is also linked to increased offspring and lifespan, giving us a better understanding of the benefits of this adaptation.
The team measured the total energy expenditure - which includes calories burned by metabolism at rest, as well as those burned during physical activity - in both humans and great apes over the course of seven to 10 days during the course of normal living behavior.
Overall, the study examined 141 humans, 27 chimpanzees, eight bonobos, 10 gorillas and 11 orangutans. Human data stemmed from a separate study called the Modeling the Epidemiological Transition Study (METS), which included adults from the U.S., South Africa, Ghana, Seychelles and Jamaica and aimed to shed light on the relationship between physical activity and energy expenditure and weight gain in adults.
The results revealed that body fat percentage was significantly higher in humans, and in addition, only humans showed a gender difference, with 22.9 percent body fat in men and 41.7 percent in women.
Humans and great apes share a close evolutionary history and together make the hominoid superfamily. The findings could help scientists uncover new ways to fight 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.
