Elephants are the gentle giants of the animal kingdom. They will often empathetically reach out their trunks to console a distressed sister or attempt to lift up those that are ill and suffering. They recognize the bones of deceased elephants and appear to mourn their dead. They also recognize themselves in mirrors—a sign they’re self-aware. These traits may have evolved because elephants have domesticated themselves, according to a study published today in the Proceedings of the National Academy of Sciences. If so, that would make them the only known animal besides humans and bonobos to have done so. But not everyone sees it as an open-and-shut case.
Proving that any animal, let alone elephants, has self-domesticated is a challenge, says Richard Wrangham, a Harvard University primatologist who was not involved in the new study. Yet he and evolutionary anthropologist Brian Hare of Duke University have long held that self-domestication—a phenomenon where wild animals develop traits that are similar to domesticated animals—must be “widespread,” Wrangham says, perhaps found in numerous species from mice to whales and elephants. Showing it in pachyderms would bolster that argument.
Most of us are familiar with the outward signs of domestication: a tamer personality and babylike features. Domesticated animals also tend to have smaller brains than their wild counterparts. By all of these metrics, dogs, cats, and pigs easily qualify.
But in each of these cases, humans played a direct role. Our ancestors favored (either consciously or unconsciously) desirable traits that became engrained over thousands of years. Not so with humans ourselves.
Studies have shown that over the past 80,000 years, our faces have shortened and our brow ridges and brains have shrunk. These changes accelerated about 10,000 years ago after the invention of agriculture. Perhaps because of a greater need for cooperative males, highly aggressive males were eliminated, researchers like Wrangham have suggested. Via self-domestication, we lengthened our childhoods, came to prefer more gregarious men (and to dislike bullies), and increased our ability to communicate and share complex ideas with language.
Since then, researchers have shown something similar in one of our closest relatives, bonobos. Close cousins of chimpanzees, bonobos are far less aggressive, have softer and rounder facial features, and a much-celebrated love of sex (they use it not just for mating, but also to make friends and soothe social conflicts) that Wrangham and Hare point to as clear signs of self-domestication. Certainly, humans were not involved in the process. But via natural selection and an abundance of food, more aggressive males were weeded out in favor of those with milder temperaments, helping to create a more peaceful society, Hare has theorized.
Other examples of self-domestication in the animal kingdom have proven elusive—until now. In the new study, Limor Raviv, an evolutionary linguist at the Max Planck Institute for Psycholinguistics, and colleagues plowed through the scientific literature, looking for species besides bonobos that showed features of being domesticated, but had limited historical contact with humans.
Only elephants—all three species (African savanna and forest elephants, as well as Asian elephants)—qualified. Like humans and bonobos, these species have low levels of aggression, and violence within and among groups is relatively rare, the researchers assert. They exhibit “increased prosociality”—going out of their way to protect and comfort others. And like humans (but not bonobos), their cortisol levels—the primary stress hormone—rise when the animals face socially difficult situations, such as mass deaths from poaching or culling. In all, the researchers documented 19 cognitive, behavioral, and physiological traits common to humans, bonobos, and elephants, but not other species.
Next, the team drilled into the genome of African elephants, finding 674 genes that appear to be evolving rapidly. They compared these genes with a set of 764 genes others have identified as important to mammal domestication, such as those involved with sociality and the management of aggression. Their analysis revealed that several of the 674 genes were associated with domestication.
It’s not yet clear what types of environmental pressures might have led elephants to develop traits that we associate with domestication, Raviv says. But she speculates that their massive size alone helps protect them from possible predators. “They can be slightly less concerned and more relaxed.”
“It’s nice to see the correlations with bonobos and humans and the genetic similarities tied to the reduction of aggression,” says Melinda Zeder, an emeritus archaeologist and domestication expert at the Smithsonian Institution. But she’s still skeptical of the self-domestication idea in general, arguing it is a “meaningless term that muddies the waters.” For her, domestication requires “two to tango”—a domesticator and a domesticate.
Wrangham agrees that the study reveals some hints of self-domestication in elephants. “The preliminary genetic evidence is promising,” he says. The work, he adds, supports a prediction that he and others have made that self-domestication is likely to be more prevalent in the animal kingdom than many researchers had assumed.
Still, Wrangham argues that many of the behavioral traits the researchers saw may simply be due to elephants’ large brains, not necessarily to self-domestication. The authors “need to consider alternate hypotheses,” he says.
As such, he says, more work will need to be done before scientists add elephants to the exclusive club that seemingly only humans and bonobos belong to. “I fear we are a long way from being able to say elephants are self-domesticated.”
Source: Science Mag