Can Animals ‘Domesticate” Themselves?

Why some wild animals are becoming nicer

08 February 12

Nature is supposed to be red in tooth and claw, and domestication an artificial process for making animals gentle. But it appears that some corners of the animal kingdom are becoming kinder, gentler places. Certain creatures may be domesticating themselves.

This possibility is most apparent in bonobos, a close cousin of chimpanzees. Unlike their violent cousins, bonobos are generally peaceful. And while many animals have evolved to be socially agreeable, bonobos — and possibly other species –seem to be experiencing something more precise and profound: the physical and behavioural changes specifically described in studies of domestication, but as a natural evolutionary process.

“Normally you think of domestication as something that happens at the hands of humans,” said Brian Hare, a Duke University evolutionary anthropologist and co-author of a bonobo research review published Jan. 20 in Animal Behaviour. “The idea that a species domesticated itself is a bit crazy, but there are some species that outcompeted others by becoming nicer.”

The essence of domestication is a loss of aggression. Because this is such a basic trait, involving modifications to nervous and endocrine systems, and alterations of complex gene networks with multiple functions, it generates a variety of changes. Researchers call them a “domestication syndrome,” and while aspects are seen in all domesticated animals, the principles are distilled in a famous Russian experiment on foxes.

Starting in 1959 with 130 farm-bred but wild foxes and continuing until today, researchers allowed only those individuals most tolerant of human contact to breed. In less than 50 years, the fierce-tempered and untouchable foxes became playful, face-licking sweethearts who loved to be held. Those traits are typically seen in wild pups, but disappear as they grow up.

With juvenile behaviours came juvenile appearances: Even as adults, foxes in the experiment now have spotted coats, floppy ears, curly tails and short legs. They’re evolutionarily suspended in childhood — and that, said Hare, may explain bonobos. “I have a lot of bonobos who are ‘friends,’ and I look at them and say, ‘I don’t understand how you evolved. You are too goofy, too nice, too silly. How did you not get eaten?” he said. “But they are very successful.”

Bonobos are very different than chimpanzees, from whom they split taxonomically about one million years ago. Chimp males struggle constantly and violently for dominance; bonobo males almost never fight, and stage virility contests involving non-confrontational stick-dragging. Male chimps often coerce females into sex; bonobos ask for permission. At the group level, chimpanzees regularly engage in something like low-level warfare, with lethal consequences; bonobos don’t. Mostly they hang out, play, and exchange sexual favors with frequency so astounding they’ve become pop-culture tropes.

Lab tests back up in-the-wild observations. Relative to chimps, bonobos are stressed by competition, attentive to others’ needs, and eager to cooperate and share. Brain regions crucial to behaviour and development, like the amygdala and occipital frontal cortex, are arranged differently. And in keeping with theories of domestication, bonobos play like juvenile chimpanzees, but throughout their lives. Their skulls also have smaller jawbones and teeth, or what anatomists call “paedomorphic” — child-shaped — features. They also have a white tail tuft and extra-pink lips, a possible analogue to the white spots often seen in, for example, cats and dogs.

According to Hare and study co-author Richard Wrangham, one of the world’s foremost primatologists, these are likely signs of domestication. But why and how could natural selection tame the bonobo? One possible narrative begins about 2.5 million years ago, when the last common ancestor of bonobos and chimpanzees lived both north and south of the Zaire River, as did gorillas, their ecological rivals. A massive drought drove gorillas from the south, and they never returned. That last common ancestor suddenly had the southern jungles to themselves.

As a result, competition for resources wouldn’t be as fierce as before. Aggression, such a costly habit, wouldn’t have been so necessary. And whereas a resource-limited environment likely made female alliances rare, as they are in modern chimpanzees, reduced competition would have allowed females to become friends. No longer would males intimidate them and force them into sex. Once reproduction was no longer traumatic, they could afford to be fertile more often, which in turn reduced competition between males.

“If females don’t let you beat them up, why should a male bonobo try to be dominant over all the other males?” said Hare. “In male chimps, it’s very costly to be on top. Often in primate hierarchies, you don’t stay on top very long. Everyone is gunning for you. You’re getting in a lot of fights. If you don’t have to do that, it’s better for everybody.” Chimpanzees had been caught in what Hare called “this terrible cycle, and bonobos have been able to break this cycle.” In doing so, they rose to primate supremacy in a region roughly the size of the United States east of the Mississippi River, and reigned unchallenged until Homo sapiens came along.

All this, at least, is the hypothesis: It’s important to note that it’s a proposed rather than certain scenario. It’s at least conceivable, if highly unlikely, that bonobos started out peaceful and chimpanzees became more aggressive. Conclusive proof would require a time machine. Still, the evidence is suggestive and the scenario plausible.

“High aggression is likely costly,” said Frank Albert, an evolutionary anthropologist at Princeton University who studies the genetics of domestication. “So it seems not very surprising that some of the bonobo-chimp ancestors may have benefited from evolving reduced aggression — and eventually become today’s bonobos.”

Not that bonobos will soon be peeking out of cardboard boxes on Cute Overload. On the trajectory from wild to domestic, they’re something likecertain wolves were tens of thousands of years ago, after reduced aggression allowed them to exploit a new ecological niche at the edges of growing human settlements, said Hare. At that time, people hadn’t yet started keeping and breeding dogs. Once they did, it accelerated a domestication already naturally underway.

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On the Domestication of Dogs

The skull of a domesticated canine.

The skull of the fossil dog found in Siberia.

Photograph courtesy Yaroslav Kuzmin, PLoS ONE

Christine Dell’Amore   National Geographic News  Published August 19, 2011

It took 33,000 years, but one Russian dog is finally having its day.

The fossilized remains of a canine found in the 1970s in southern Siberia’s Altay Mountains (see map) is the earliest well-preserved pet dog, new research shows.

Dogs—the oldest domesticated animals—are common in the fossil record up to 14,000 years ago. But specimens from before about 26,500 years ago are very rare. This is likely due to the onset of the last glacial maximum, when the ice sheets are at their farthest extent during an ice age.

With such a sparse historical record, scientists have been mostly in the dark as to how and when wolves evolved into dogs, a process that could have happened in about 50 to a hundred years.

“That’s why our find is very important—we have a very lucky case,” said study co-author Yaroslav Kuzmin, a scientist at the Russian Academy of Sciences in Novosibirsk.

In the case of the Russian specimen, the animal was just on the cusp of becoming a fully domesticated dog when its breed died out.

(See dog-evolution pictures.)

Dogs Arose at Multiple Sites?

Kuzmin and colleagues recently used radiocarbon dating to examine the skull and jaw of the Russian dog in three independent laboratories. Each lab confirmed the fossil’s age at around 33,000 years old.

Burnt twigs also found at the site, known as Razboinichya Cave, suggest that hunter-gatherers used the space for something, and it’s likely the dog was their pet before its death from unknown causes, Kuzmin said.

Cold temperatures and nonacidic soil in the cave likely kept the dog’s remains from completely decaying, he added.

The team compared the Russian dog fossils with the bones of wild wolves, modern wolves, domesticated dogs, and early doglike canids that lived before 26,500 years ago.

The results showed that the dog—which probably looked like a modern-daySamoyed—most closely resembled fully domesticated dogs from Greenland in size and shape. That’s not to say the two dog types are related, though, since the new study didn’t run DNA analysis.

Because it wasn’t fully domesticated, the Russian dog retained some traits from its ancestors—namely wolf-like teeth. But the animal bore no other resemblance to ancient or modern wolves or to dog breeds from elsewhere in Russia, Kuzmin and colleagues found.

The discovery suggests that this dog began its association with humans independently from other breeds, which would mean that dog domestication didn’t have a single place of origin—contrary to some DNA evidence, the study said.

Curious Wolves Went to the Dogs

In general, dogs likely became domesticated when curious wolves began to hang around Stone Age people, who left butchered food remnants littering their camps, according to study co-author Susan Crockford, an anthropologist and zooarchaeologist at the University of Victoria in Canada.

This phenomenon occurred in Europe, the Middle East, and China, according to the study, published July 28 in the journal PLoS ONE.

Animals that were more comfortable around humans underwent changes in their growth rates—probably regulated by hormones—that eventually changed their reproductive patterns, sizes, and shapes, turning them into dogs, Crockford said by email.

For example, dogs became smaller, developed wider skulls, and gave birth to bigger litters than wolves, she said.

“The somewhat curious and less fearful ‘first founders’ became even more so as they interbred amongst themselves,” Crockford said.


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