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The War That Made Elephants Born Without Tusks

Between 1977 and 1992 Mozambique suffered a bloody civil war that caused a million deaths. To finance the conflict, poachers from both sides systematically hunted African elephants ( Loxodonta africana ) in Gorongosa National Park, with the aim of obtaining their precious ivory.

The slaughter rapidly reduced the population of these animals but, in addition, it had an unexpected consequence: the number of females born without tusks increased considerably . A dramatic example of how human pressure can influence the evolution of a species.

Typically more than 90% of female African elephants have tusks. But in places where poaching has been extensively practiced, such as Gorongosa, females without poaching are surprisingly common. It is a tragedy, but an unprecedented opportunity for scientists to understand the extent of human impact on animals in their natural habitat.

In a situation where a species is killed for its tusks, not having them is clearly a biological advantage. And if there is less chance of being hunted , there is more of passing those genes without fangs to the next generation. After the war, the proportion of Gorongosa tuskless females increased by more than 30% as the elephant population – currently about 700 individuals in the park – declined by more than 90%, suggesting an evolutionary response. .

Shane Campbell-Staton of Princeton and California University in Los Angeles and his team carried out simulations that showed that the increase in individuals lacking this anatomical trait would have been extremely unlikely without the selective killing of the tusked animals. . As explained this week in the journal ‘Science’, the survival of individuals without fangs was five times greater than that of individuals that did have them.

Lethal to males
The females were born without tusks but no cases were recorded among the males. The researchers studied the genes that have to do with the development of teeth in mammals and found two (AMELX and MEP1a) that were key. The former is involved in the formation of enamel and dental cementum, the bone-like tissue that serves to fix the tooth, while the latter is involved in the formation of dentin, the tissue beneath the enamel.

‘The data we have collected suggests that the lack of fangs has a lethal effect on males, so that those who inherit the gene for the trait are never born or die quickly. A human disease syndrome associated with the same region of the X chromosome is also lethal for men , while affected women often do not develop their upper lateral incisors, the human equivalent of elephant tusks, ”Campbell explains in an email. -Staton.

Evolution is something that has been happening for a long time, but this study shows that it is also something that is happening now and around us. And we are participating in that process. “Over the past two decades, we have gathered increasing evidence that humans are an extreme pressure affecting the evolution of many species. Hunting, cities, pollution and many other characteristics of human life force animals and plants to adapt to live with us, ”says the researcher.

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