"Elephants losing tusks in unnatural selection" (2005)

The tusk-free gene, which is found in 2 to 5 per cent of male Asian elephants, has increased to between 5 and 10 per cent in elephants in China, according to a study by Zhang Li, an associate professor of zoology at Beijing Normal University.

"This decrease in the number of elephants born with tusks shows the poaching pressure for ivory on the animal," said Mr Zhang, who has been conducting research since 1999 at a nature reserve in the lush southwestern Xishuangbanna region, where two-thirds of China's Asian elephants live.

Unlike African elephants, only the male Asian elephant has tusks, which he uses as a weapon to fight for territory. But they are prized by hunters and regarded by Chinese as a symbol of masculinity.

The elephant's pride has been its death sentence. China is one of the world's biggest centres for smuggling ivory.

"The larger tusks the male elephant has, the more likely it will be shot by poachers," Mr Zhang said. "Therefore, the ones without tusks survive, preserving the tuskless gene in the species."

The phenomenon was not the result of natural causes. "It is a reluctant choice made in the face of a gun."

China is one of 160 nations that signed a treaty in 1989 banning the trade in ivory and products of other endangered animals. Trade in Asian elephant ivory had been banned since 1975.

Despite the ban, four Asian elephants were shot in China last year. Because of the rampant killing of male elephants for ivory, the female-to-male ratio had changed from the ideal of 2:1 in China to 4:1, whereas in India the ratio was 100:1, Mr Zhang's report said.

That uneven ratio was attributable to the dramatic reduction in the fertility of the species and the depletion of its gene pool, Mr Zhang said. Some academics have questioned Mr Zhang's assertion that evolution was playing a role in saving the elephant. "This is, of course, a possibility, but till now there is no clear genetic proof that it can occur," said Vivek Menon, executive director of the Wildlife Trust of India.