Not a bull market: as cows narrow the gender difference with males of the species, are elephants at risk of dying out?

Study by Chinese team suggests female elephants are getting less turned on by bulls as they adopt traits once harboured by them

PUBLISHED : Thursday, 07 April, 2016, 9:01am
UPDATED : Monday, 12 June, 2017, 12:53pm

The world’s biggest land animal,as immortalised in the Disney classic Dumbo and revered in godlike form according to Hindu iconography, may be in danger of dying out - and not for its prized tusks - according to a new study by Chinese scientists.

The Chinese team concluded that cows (females) are getting less turned on by their male partners (bulls) as the physical differences between the two sexes continues to shrink over time, meaning they are mating less often and creating fewer offspring.

Elephants live for up to 60 years but require 22 months’ gestation and can only have one calf at a time.

Their forebears once served as a major source of protein for Homo erectus (“upright man”) and are now hunted for their ivory tusks in Africa and Asia. But the waning pulling power of even alpha males could prove the undoing of the species, according to the Chinese scientists.

Elephants’ early ancestors appeared more than 50 million years ago and thrived during a geological epoch known as the Miocene that began 23 million years ago. But the global population dwindled 5 million years, as did their diversity. Now just three species remain alive on earth.

Their decline has left most evolutionary biologists puzzled as it occurred long before the appearance of early humans 2 million years ago.

Using fossil records from North America, Europe and China, including some of the freshest specimens from a Miocene burial site in Hezheng city, in west China’s Gansu province, the Chinese team pored through the evolutionary history of elephants to find answers.

They found that the animal’s sexual dimorphism, or the difference in the body design of male and female beyond the sexual organs, was far stronger during the Miocene period than either before or after.

The team, led by Deng Tao and Wang Shiqi, two researchers from the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, published their findings in the journal Vertebrata PalAsiatica.

Their paper states that bulls had much longer trunks and more protruding foreheads than cows during the Miocene. However, those difference have all but disappeared in modern-day elephants.

This might have made cows much pickier when it comes to choosing a mate, thus leading to a decline in both population size and their biodiversity, the researchers suggested.

Such a narrowing of the gender gap has been observed in other mammals like horses, rhinos and giraffes, all of which are also approaching an evolutionary dead-end, Deng and Wang reported.

Yet other big animals like antelopes and buffaloes maintain a strong sexual dimorphism (physical difference) and are continuing to evolve in a healthy way.

The scientists wanted to know why this was true for some species but not for others, especially elephants.

One possible explanation is that cows may prefer males with longer trunks, which make them more adept at gathering food and physical combat. But when the females acquired the trait themselves, the male could have become less attractive to them.

Generally speaking, female elephants have had the upper hand in dictating the evolution of the species, according to the researchers.

“As is the case with humans, males can attract females by various forms of direct or indirect competition with other males, but the ultimate decision is often up to the female,” they wrote.

Yet it would be premature to assume the convergence of sexual patterns would automatically result in the extinction of a species, according to Professor Gao Fei, a researcher of developmental biology at the Institute of Zoology in Beijing.

“Some simple life forms have very weak sexual dimorphism, but they have lived on this planet for hundreds of millions of years,” he said.