Some elephants have developed a genetic mutation that protects them from being hunted for ivory: females are born without tusks
Human activities have had a substantial impact on nature since the days when humans first began cultivating the land and hunting or domesticating wild animals. What is under close scrutiny by scientists today is the important effect of human presence on the evolution of some species.
The pressure of humans on natural ecosystems has acquired such dimensions that it can be considered a real evolutionary factor. A study recently published in Science shows that it is precisely because of humans that female elephants in Mozambique are losing their tusks, and they are not the only animals changing because of us.
Elephants are losing their tusks
Apparently, female elephants are evolving in a way that does not retain their tusks. The cause of the phenomenon was intuitable, but the confirmation comes only from the research of Shane Campbell-Staton and colleagues, of Princeton University: elephants are losing their tusks because of man.
In particular, thanks to the study of historical videos that were compared with the current situation, it was possible to quantify the phenomenon, and place it temporally in a period that would seem to leave no room for other hypotheses.
It emerged that between 1977 and 1992 the number of females born without tusks increased from 19 to 51%: these were the years of the Civil War in Mozambique, during which both sides in the conflict were engaged in major poaching sessions aimed at collecting ivory, now illegal in most of the world.
As a result of the heavy hunting actions, the total population of elephants in Gorongosa National Park decreased in those years by 90%: this is also why, according to scientists, we can clearly speak of "evolutionary pressure" at the hands of man. Just after the end of the conflict, in fact, the number of female elephants born with tusks slowly increased again.
The statistical analysis conducted by the research team show that the emergence of such a phenomenon is highly unlikely in the absence of an important trigger, such as a selective pressure capable of modifying the evolution of elephants. So it is certain that the loss of tusks is related to the human activity of ivory hunting, in this and other cases.
Man as a factor of evolutionary pressure
Strangely, continues the research, the phenomenon studied in Mozambique involves only female elephants, and the reason lies in what is called a "genetic oddity".
The genetic mutation at the base of the loss of the tusks would reside in one of the X chromosomes of the elephants: exactly as it happens for humans, female elephants have two X chromosomes, while males have only one.
The mutation of the only X chromosome is lethal for male elephants, while in females the presence of the second X chromosome allows the mutation to spread without health effects.
This does not take away from the fact that ivory hunting has also had consequences on male elephant populations: today in Sri Lanka less than 5% of elephants are born with tusks. And thanks to Campbell-Staton's research, we know for sure that the basis of this genetic modification is human ivory hunting - in Sri Lanka as in Mozambique.
The genetic oddity that has, for now, "saved" the tusks of African male elephants, therefore, does not reassure the scientific community at all.
"Tusks are pretty much the elephants' Swiss Army knife," says Campbell-Staton, which is why the loss of tusks may help elephants escape poachers, but it seriously complicates the lives of the animals, who use their tusks to obtain water and food.
Many animals depend indirectly on elephant tusks: "that's what preserves biodiversity," Campbell-Staton concludes, and reminds us that "our actions can have consequences like these."