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Ivory poaching over decades led to the evolution of elephants without tusks

Gorongosa National Park elephants

GORONGOSA NATIONAL PARK, MOZAMBIQUE-NEWS AND COMMENT: This is an interesting example of how the intervention of humans can inadvertently alter the course of evolution. The story is also interesting for the fact that, looking at the story from a different angle, it is as if nature is protecting elephants.

Gorongosa National Park elephants

Gorongosa National Park elephants. Photo: Idaho Statesman/MCT via Getty Images,

The process is simple. In Gorongosa National Park, between 1977 and 1992, 90% of the elephant population were slaughtered by armed forces during the Mozambican Civil War. They killed them for their ivory which they sold to fund their fighting. Obviously they did not kill elephants without tusks.

This led to the simple fact that almost all the elephants that were left alive did not have tusks. And so these tuskless elephants were the only ones left to breed. And of course they produced offspring that grew up to be tuskless (only females – see below).

They were, in effect, engaging in artificial selection because they were culling a certain type of elephant namely one with tusks, and leaving the tuskless elephants alone. When you cull a section of animals you are, as mentioned, engaging in a form of ‘selective breeding’. It’s a bit like a cat breeder selecting a foundation cat for their breeding line.

Inadvertently, these poachers were “selecting” tuskless elephants. Apparently it took as little as a couple of generations for the effects to be felt. And the effect is still noticeable today among the group of 700 elephants that live in the National Park.

Robert Bingle of the Department of Ecology and Evolutionary Biology at Princeton University said that it is an example of the impact of human interference in nature. He said: “What I think this study shows is that it’s more than just numbers. The impacts that people have, we’re literally changing the anatomy of animals.”

But why were there tuskless elephants in this park? He said that a feature of the herd of elephants in this park is that a lot of the female elephants didn’t have tusks and they were intrigued by it. At that time nobody understood, although many people had observed the apparent abnormality in this group of elephants. Also nobody had really quantified or documented the phenomenon. They thought tusklessness might have been linked to the gender of the elephants.

And indeed, they discovered that mutated genes resulted in the stalling of the growth of lateral incisors. This meant that female elephants did not grow tusks which in turn protected them from the poachers. However, the mutated genes are fatal to male elephants as they do not develop properly in the womb.

Half of male elephant calves with a tuskless mother will have the genetic abnormality. This resulted in herds being severely depleted in male elephants. The problem has been reversed over time. They expect the problem to decrease in frequency provided conservation is maintained.

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