How humans evolved to be ‘energetically unique’

Amazing stuff! Sweating, long recognized as one of humans advantages, is not the only factor that improved intelligence, reproduction and longevity.

"Humans, it turns out, possess much higher metabolic rates than other mammals, including our close relatives, apes and chimpanzees, finds a new Harvard study. Having both high resting and active metabolism, researchers say, enabled our hunter-gatherer ancestors to get all the food they needed while also growing bigger brains, living longer, and increasing their rates of reproduction. ...

Using a new comparison method that they say better corrects for body size, environmental temperature, and body fat, the researchers found that humans, unlike most mammals including other primates, have evolved to escape a tradeoff between resting and active metabolic rates. ...

In other primates, there is a distinct tradeoff between resting and active metabolic rates, which helps explain why chimpanzees, with their large brains, costly reproductive strategies, and lifespans, and thus high resting metabolisms, are “couch potatoes” who spend much of their day eating ..."

From the significance and abstract:

"Significance

There is debate over whether primate and human metabolic rates are lower than those of other animals and whether higher physical activity levels cause lower resting metabolic rates. Here, we describe a method for comparing metabolic rates using quotients of measured metabolic rates versus those predicted from a large sample of mammals corrected for the effects of body size and composition, environmental temperature, and evolutionary relatedness. Applying these metabolic quotients to several human populations reveal that humans evolved exceptionally high metabolic rates that, unlike other mammals including nonhuman primates, do not trade off energy allocation to maintenance versus physical activity. Humans’ uniquely high metabolic rates helped fuel the evolution of our species’ large brains, high reproductive rates, and extended longevity.

Abstract

All organisms use limited energy to grow, survive, and reproduce, necessitating energy allocation tradeoffs, but there is debate over how selection impacted metabolic budgets and tradeoffs in primates, including humans. Here, we develop a method to compare metabolic rates as quotients of observed relative to expected values for mammals corrected for size, body composition, environmental temperature, and phylogenetic relatedness. Contrary to previous analyses, these quotients reveal that nonhuman primates have total metabolic rates expected for similar-sized mammals in similar environments. In addition, data from several small-scale societies show that humans evolved exceptionally high resting, activity, and total metabolic rates apparently by overcoming tradeoffs between resting and active energy expenditures that constrain other primates. Enhanced metabolic rates help humans fuel expanded brains, faster reproductive rates, extended longevity, and high percentage of body fat."

How humans evolved to be ‘energetically unique’ — Harvard Gazette "Metabolic rates outpaced ‘couch potato’ primates thanks to sweat [???], says new study"

Metabolic scaling, energy allocation tradeoffs, and the evolution of humans’ unique metabolism (no public access)

Comparisons of resting, active, and total metabolic quotients among various species and human populations, as defined by the Harvard researchers’ new method.