Orangutan at Rest: How very stereotypical.
That orangutan you see at the zoo doing nothing but sitting on its rump staring at you (no matter how hard you bang on its plexi-glass cage), is indeed as lazy as you thought.
According to a new report
penned by anthropology professor Herman Pontzer
at Washington University in St. Louis, orangutans confined to indoor/outdoor enclosures use less energy, relative to body mass, than nearly any eutherian mammal ever measured, including sedentary humans.
The findings follow a two week study of orangutans living in the 230-acre Great Ape Trust in Des Moines, Iowa. Never before has such an extremely low rate of energy use been observed in a primate. Moreover, the study reports that orangutans living in the wild are similar low-energy creatures.
Pontzer and his colleagues conclude that the low energy is "consistent
with the slow growth and low rate of reproduction
in orangutans, and may be an evolutionary response to severe food
in their native Southeast Asian rainforests."
Interesting. But what we really want to know is just how lazy (or energy efficient, you might say) are orangutans when compared to humans? Today Pontzer responded to an email from Daily RFT
To put some numbers on the human/orangutan comparison: a recent large
study of normal weight adult human women living in Texas (Butte et al
2003 American Journal of Clinical Nutrition) found that on average,
women weighing 125 lbs burn about 2400 kilocalories per day. By
comparison, the adult female orangutans in our study, which also weigh
125 lbs, burn about 1600 kilocalories per day. So the difference is
actually pretty large.
There are a lot of studies out there like the one you suggest --
measuring energy use in sedentary humans (go to PubMed, the NIH database
for research articles, and search "human doubly labeled water" and you
get about 550 hits). One thing that is striking if you look at those
articles: the "2000 calories a day" benchmark that people often use/cite
as normal for adults is bogus -- people generally use more. So the
energy used by orangutans is remarkably low compared to us.