New research
shows that humans and other primates burn 50% fewer calories each day than
other mammals. The study, published January 13 in the Proceedings
of the National Academy of Sciences, suggests that these remarkably slow metabolisms
explain why humans and other primates grow up so slowly and live such long
lives. The study also reports that primates in zoos expend as much energy as
those in the wild, suggesting that physical activity may have less of an impact
on daily energy expenditure than is often thought.
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Most mammals,
like the family dog or pet hamster, live a fast- paced life, reaching adulthood
in a matter of months, reproducing prodigiously (if we let them), and dying in
their teens if not well before. By comparison, humans and our primate relatives
(apes, monkeys, tarsiers, lorises, and lemurs) have long childhoods, reproduce
infrequently, and live exceptionally long lives. Primates’ slow pace of life
has long puzzled biologists because the mechanisms underlying it were unknown.
An
international team of scientists working with primates in zoos, sanctuaries,
and in the wild examined daily energy expenditure in 17 primate species, from
gorillas to mouse lemurs, to test whether primates’ slow pace of life results
from a slow metabolism. Using a safe and non-invasive technique known as
“doubly labeled water,” which tracks the body’s production of carbon dioxide,
the researchers measured the number of calories that primates burned over a 10-day
period. Combining these measurements with similar data from other studies, the
team compared daily energy expenditure among primates to that of other mammals.
“The results
were a real surprise,” said Herman Pontzer, an anthropologist at Hunter College
in New York and the lead author of the study. “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.”
This dramatic
reduction in metabolic rate, previously unknown for primates, accounts for
their slow pace of life. All organisms need energy to grow and reproduce, and
energy expenditure can also contribute to aging. The slow rates of growth,
reproduction, and aging among primates match their slow rate of energy
expenditure, indicating that evolution has acted on metabolic rate to shape
primates’ distinctly slow lives.
Read more at the Lincoln
Park Zoo.
Gorilla
image via Shutterstock.