Tigra Scientifica: Mammals and Metabolism

Slow energy expenditure may lead to longer lives.


April 4, 2014

“Mammals typically live fast-paced lives, mature in a few months, reproduce prodigiously and die in their teenage years, if not before,” Sharon Dewar, public relations director of Lincoln Park Zoo, said. However, humans and other primate relatives take years to mature, reproduce infrequently and live long lives.

But why? Herman Pontzer, an anthropologist at Hunter College, New York, along with other colleagues, compared average daily energy expenditure of animals at Lincoln Park Zoo in Chicago, discovering new information about primate metabolism. Published on Jan. 13, 2014 in “Proceedings of the National Academy of Sciences,” the study suggests that a slow metabolism explains why humans and other primates mature slowly and live relatively long lives.

The international team of scientists conducted a study of primates in zoos, sanctuaries and in the wild, where they examined daily energy expenditure in seventeen primate species, to test the theory that a primate’s slow pace of life results from a slow metabolism. Rachel Nuwer of “SmithsonianMag.com” explains that they measured metabolic rate using an established method called “doubly labeled water,” which involves dosing the study subject with a specific, non-radioactive isotope of oxygen and observing the rate that the subject’s body processes it into carbon dioxide. This method allowed the researchers to measure the number of calories burned (or average metabolic rate) over a 10-day period. After collecting data from the primates, researchers compared daily energy expenditure to known values in other mammals.

Results show that when controlling for body size, primates burn about 50 percent fewer calories than other mammals. “The results were a real surprise,” Pontzer said, “Humans, chimpanzees baboons, and other primates expend only half the calories we’d expect for a mammal. To put that in perspective, a human — even someone with a very physically active lifestyle — would need to run a marathon each day just to approach the average daily energy expenditure of a mammal their size.”

Just as surprising, the results of the study also show that primates in captivity and primates in the wild expend a similar amount of calories daily, suggesting a niche for energy expenditure within the species. Therefore, physical activity may contribute less to total energy expenditure than is often thought. “It…sheds light on the fact that zoo-housed primates are relatively active, with the same daily energy expenditures as wild primates,” co-author Steve Ross, director of the Lester E. Fisher Center for the Study and Conservation of Apes at Chicago’s Lincoln Park Zoo, said.

These results suggest an inherent level of physical activity an animal will expend, regardless of lifestyle. “The finding offers a completely new way to understand why primates have slower life histories than other mammals of equivalent body size,” Erin Vogel, Primatologist of Rutgers Universit, said. Energy expenditure is thought to contribute to aging; therefore, a slow rate of growth and reproduction among primates indicates that evolution may have acted on metabolic rate to shape primates’ distinctly slow lives.

Implications of these results may allow for a greater understanding of health and longevity in humans by clarifying the processes by which humans develop and age.

Lincoln Park Zoo reports that a more detailed study of energy expenditure, activity, and aging among humans and apes is already underway.

“Humans live longer than other apes, and tend to carry more body fat,” Pontzer said.

“Understanding how human metabolism compares to our closest relatives will help us understand how our bodies evolved, and how to keep them healthy.”

Originally published by TheTigerNews.com