How humans evolved to be “energetically unique” — Harvard Gazette

Humans have a much higher metabolic rate than other mammals, including closely related apes and chimpanzees, a new study from Harvard University has found. Researchers say a combination of high rest and active metabolism allowed our hunter-gatherer ancestors to get all the food they needed, while growing bigger brains, living longer, and increasing reproductive rates. It is said that he did.

“Humans are unlike any other known creature in terms of how they use energy, and it's off the beaten track,” says study co-author and paleoanthropologist. Daniel LiebermanEdwin M. Lerner Professor of Biological Sciences in the Department of Human Evolutionary Biology.

The paper, published on Monday, Proceedings of the National Academy of Scienceschallenge the previous consensus that humans and nonhuman primates have the same metabolic rate or a lower metabolic rate than would be expected given their body size.

Using a new comparative method that better corrects for body size, environmental temperature, and body fat, the researchers found that humans, unlike most mammals, including other primates, have different rates of resting metabolic rate and activity. They found that humans have evolved to avoid trade-offs between metabolic rates.

Animals ingest calories through food and, like bank accounts, spend those calories primarily in two broad metabolic categories: rest and physical activity. In other primates, there is a clear trade-off between resting and active metabolic rates, which suggests that chimpanzees with large brains, expensive reproductive strategies, longevity, and therefore high resting metabolism, but with less sleep This helps explain why they are “couch potatoes” who spend so much of their time. “I eat all day long,” Lieberman said.

In general, the energy an animal spends on metabolism ends up as heat, and heat is less dissipated in warmer environments. Because of this trade-off, animals such as chimpanzees, which expend significant energy on resting metabolism and live in warm tropical environments, must maintain low activity levels.

“Not only have we increased our resting metabolism beyond chimpanzees and monkeys, but we have also been able to increase our physical activity levels without reducing our resting metabolic rate, thanks to our unique ability to release heat through sweating. ” said the co-author. Andrew Yejiana senior researcher in the Lieberman lab.

“As a result, we are an energetically unique species.”

The researchers' analysis shows that monkeys and apes have evolved to invest about 30 to 50 percent more calories in their resting metabolic rate than other mammals of the same size, and humans have evolved to invest even more calories in their resting metabolic rates. Extremely, they have been shown to invest 60 percent more calories than similar mammals. large mammal.

“We started with the question whether humans and other primates may have a relatively low total metabolic rate. suggested by other researchers” said Yegian. “We tried to find a better way to analyze it using quotients, and that's when we stepped on the gas.”

The research team, which includes collaborators from Pennington Biomedical Research Center in Louisiana and Kiel University in Germany, will further investigate metabolic differences between human populations. For example, subsistence farmers who grow all the food they eat without the aid of machinery have significantly higher levels of physical activity than both hunter-gatherers and people living in industrial environments like Americans. However, all humans, regardless of their activity level, spend a similar amount of energy on their resting metabolic rate, depending on their body size.

“What we're really interested in is the variation in human metabolic rates, especially in today's world with advances in technology and declining levels of physical activity,” Yegian says. “We have evolved to be active, but how does sitting at a desk change our metabolism and affect our health?”