Absorbing research on human sweat
Sweat and its role in human evolution feature in two intriguing studies by UK researchers. Scientists at Loughborough University have compiled a “sweat map” of the human body. They attached super-absorbent panels of special fabric, which can soak up 20 times its own weight of sweat, to male athletes exercising in hot conditions.
The results, published in the European Journal of Applied Physiology, came as a surprise. The central and lower back, particularly along the spine, showed unexpectedly high rates of sweating – twice as much as the front of the chest.
For cooling through evaporation, the main function of sweating, this is inefficient because the back is less exposed to airflow when walking or running and more sweat will simply drip off the body without cooling it.
George Havenith of Loughborough proposes a speculative evolutionary explanation: “If this pattern is a remnant from when we moved on all fours, before we walked upright, then sweating on the back would make sense. The chest would be protected from air movement and enclosed by the extremities, while the back pointing upwards would be more exposed to wind.’’
A separate study by scientists at Liverpool John Moores University and Glasgow University investigates the controversial theory that hunting animals by running them into the ground through heat exhaustion was important in human evolution. According to this long-standing idea, our ancestors evolved the ability to sweat while losing body hair so that they could stay cool enough to outrun their prey.
But the results, published in the Journal of Human Evolution, show that endurance running could not have been a factor until late in human evolution. People could only have kept cool enough to run for long periods in the African heat if they were as hairless and sweated as much as modern humans.
The big unknown, says David Wilkinson of Liverpool John Moores, is how long ago and how gradually hominids lost their body hair. Palaeontology and genetics offer no good evidence for the timing. As he points out, “it is interesting to note the very different amounts of hair that have been drawn in both academic and popular reconstructions of our ancestors.”
Asked about sweaty backs, Wilkinson says our early ancestors probably had too much hair when they walked on all fours to have sweated much through the back. But he offers another speculation: later, after they became bipedal and had more bare skin, their backs would have been exposed to the air as they knelt or bent over to forage.
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