Skin channels keep elephants cool

05 October 2018

Scientists have discovered how elephants keep cool and linked it to a common skin disease in humans.

Scientists aim to understand and provide answers to all the “why” questions. Centuries of scientific advances give us a pretty good picture about why our world is the way it is but there are still more questions. Recently, a group of scientists asked themselves “why is an elephant’s skin so wrinkly and cracked?”

Elephants are mainly found in hot countries like Africa but unlike humans, they have no sweat glands, so cannot sweat to cool down and maintain naturally moist skin. This is why you often see elephants cooling down by showering with their trunks or wallowing in the mud. The water on their skin evaporates to cool them down but the extent of cooling was previously unknown.

By combining analysis of elephant skin samples and observation of elephants in captivity, the team lead by Michel Milinkovitch at the University of Geneva, found that in addition to the usual wrinkles, there are also millions of tiny channels on the surface of the elephant skin. This network of channels allows up to 10 times more water to stick on the elephant skin’s surface after a spraying to stay cool. So how do these small channels appear?

“The network of channels is generated by material cracking” said Milinkovitch. They initially assumed that the channels formed cracks by stretching forces, like when mud dries, but this new research reveals the true reason. In elephants, as the new bottom layers of skin form, the old surface ones do not shed like in snakes or humans. Instead the dry, old layers at the surface remain stuck to the new skin. The researchers also discovered that elephants have small, isolated bumps under their skin. When this bumpy surface covered with layers of skin was studied with computer models, it shows that the build up of layers causes stress in the dry, old surface skin.  A bit like bending a ruler too much, the combined stress from the bumps and all the built up layers causes the skin to crack.

The team has connected this accumulated skin behaviour in elephants with a common genetic skin disease affecting one in 250 of us humans, Ichthyosis vulgaris. The incurable condition prevents the skin from shedding leading to painful and itchy skin with a cracked, scaly appearance. In both humans and elephants, this anti-shedding behaviour is from an internal re-writing of our genetic codes over time which determine our features. It is remarkable that the evolutionary accumulation of skin benefits elephants but hinders humans and further studying elephants skin may actually help us to understand this disease in order to find a cure for anti-shedding humans.

In particular, it is important to understand more about when exactly the elephant skin cracks. Milinkovitch observed first hand that elephants are not born with these cracks in their skin and he said he is studying an infant elephant to find out when the cracks first develop and how they spread through the surface.

So Nelly’s shower makes her as clean as a whistle and as cool as a cucumber!

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