Scientists Solve Mystery of the Cracks in Elephant Skin

A team led by researchers from the University of Geneva (UNIGE), in Switzerland, may have finally solved the mystery of how the skin of African bush elephants becomes so cracked—a characteristic that's hugely beneficial to their survival.

The skin of these animals is covered in an intricate network of minuscule, micrometer-wide crevices that retain water and mud. This helps protect the skin against parasites and solar radiation, while it also plays a significant role in regulating the elephant's body temperature and preventing dehydration.

African elephants—of which there are two species—lack the sweat and sebum glands that allow many other mammals to keep cool, so the only way they can avoid overheating in their hot, dry habitat is via the evaporation of water, which collects on their skin when they bathe, spray themselves or wallow in mud.

"The skin of African elephants is of course wrinkled, that's very visible, but if one has a much closer look, one realizes that the integument [the skin and its appendages] is also deeply sculptured by an intricate network of minuscule interconnected channels," Michel Milinkovitch, a professor at the Laboratory of Artificial & Natural Evolution at UNIGE, told Newsweek.

"This beautiful fine pattern of millions of channels is adaptive because it prevents the shedding of applied mud and allows the spreading and retention of five to 10 times more water than on the surface, allowing the animal to efficiently control its body temperature with evaporative cooling," he said.

Now, in a paper published in the journal Nature Communications, Milinkovitch and his colleagues show, for the first time, how these channels form. The team came to their conclusions using customized computer simulations that model the growth of the elephant's skin, based on CT scans of the real thing.

Milinkovitch's lab specializes in the study of the developmental and evolutionary mechanisms that generate life's complexity and diversity, particularly the physical processes that affect animal characteristics. Previously, they had found that scales on the face and jaws of crocodilians form through skin folding in a way that resembles cracks forming in drying mud.

The skin of elephants, like this one in the Arusha region in Tanzania, is covered in an intricate network of minuscule crevices that retain water and mud. This helps protect the skin against parasites and solar radiation and also plays a significant role in regulating the elephant’s body temperature. Michel Milinkovitch

"We wanted to understand how the channels on the skin of African elephants are generated," Milinkovitch said. "Was it a similar process than that we observed on the head of crocodiles?"

"The visual aspect of the cracking pattern on the skin of the African elephant bears a striking resemblance, albeit at very different spatial scales, to cracks caused by tensile stress in drying mud, in damaged asphalt," he said. "It was therefore tempting to hypothesize that the African elephant skin cracks are generated by shrinkage of the skin. We were really convinced that the pattern would be easily explained. We were wrong."

Instead, they found that the outermost layer of skin grows thicker and bends over time, resulting in fractures from mechanical stress as the animals move. In this sense, the cracks are not folds or wrinkles in the traditional sense.

At the most basic level, these findings are a new example of how physical processes are involved in the development of animal forms and shapes, according to Milinkovitch. But they could even have implications for understanding certain skin conditions in humans.

"Strikingly, we show strong similarities between the normal skin morphology of African elephants and that of humans affected by ichthyosis vulgaris, a common genetic disorder—affecting about 1 in 250 people—that is known to cause dry, scaly skin," Milinkovitch said. "If validated by future detailed molecular and cell biology comparisons, this equivalence would then make a remarkable link between a human pathological condition and the skin of an iconic species of pachyderm," he said.