Tuesday, July 25, 2006

Fast fox evolution

This Times article describes controlled (should I say directed?) breeding experiments on small mammals such as foxes and rats performed by a Siberian scientist Dmitri Belyaev. Belyaev has managed to produce nice (tame, domesticated) and nasty (aggressive) versions of each animal in a surprisingly short time by simply breeding according to exhibited trait. The tame foxes can even perform difficult cognitive tasks like reading humans well enough to determine what they are looking at -- dogs can do this, but generally smarter chimps cannot. It's a great demonstration of how fast evolution can proceed when selection pressure is strong enough. One of the fascinating side effects of selection based on behavior is that certain physical traits (in foxes: floppy ears, white patches of fur and differently shaped skulls) were also altered, so the tame foxes can be readily identified versus wild or aggressive ones. (I don't see why this would be a priori implausible: the genes for tameness might have superficial physical as well as behavioral effects.)

These results rule out any simple-minded conclusions about whether superficial physical traits might be correlated to cognitive or behavioral traits. Sub-populations that look alike might actually behave alike. Sometimes you can judge a book by its cover :-)

NYTimes: Belyaev chose to test his theory on the silver fox, a variant of the common red fox, because it is a social animal and is related to the dog. Though fur farmers had kept silver foxes for about 50 years, the foxes remained quite wild. Belyaev began his experiment in 1959 with 130 farm-bred silver foxes, using their tolerance of human contact as the sole criterion for choosing the parents of the next generation.

“The audacity of this experiment is difficult to overestimate,” Dr. Fitch has written. “The selection process on dogs, horses, cattle or other species had occurred, mostly unconsciously, over thousands of years, and the idea that Belyaev’s experiment might succeed in a human lifetime must have seemed bold indeed.”

In fact, after only eight generations, foxes that would tolerate human presence became common in Belyaev’s stock. Belyaev died in 1985, but his experiment was continued by his successor, Lyudmila N. Trut. The experiment did not become widely known outside Russia until 1999, when Dr. Trut published an article in American Scientist. She reported that after 40 years of the experiment, and the breeding of 45,000 foxes, a group of animals had emerged that were as tame and as eager to please as a dog.

As Belyaev had predicted, other changes appeared along with the tameness, even though they had not been selected for. The tame silver foxes had begun to show white patches on their fur, floppy ears, rolled tails and smaller skulls.

...There was far more to Belyaev’s experiment than the production of tame foxes. He developed a parallel colony of vicious foxes, and he started domesticating other animals, like river otters and mink. Realizing that genetics can be better studied in smaller animals, Belyaev also started a study of rats, beginning with wild rats caught locally. His rat experiment was continued after his death by Irina Plyusnina. Siberian gray rats caught in the wild, bred separately for tameness and for ferocity, have developed these entirely different behaviors in only 60 or so generations.

The collection of species bred by Belyaev and his successors form an unparalleled resource for studying the process and genetics of domestication. In a recent visit to Novosibirsk, Dr. Brian Hare of the Planck Institute used the silver foxes to probe the unusual ability of dogs to understand human gestures.

If a person hides food and then points to the location with a steady gaze, dogs will instantly pick up on the cue, while animals like chimpanzees, with considerably larger brains, will not. Dr. Hare wanted to know if dogs’ powerful rapport with humans was a quality that the original domesticators of the dog had selected for, or whether it had just come along with the tameness, as implied by Belyaev’s hypothesis.

He found that the fox kits from Belyaev’s domesticated stock did just as well as puppies in picking up cues from people about hidden food, even though they had almost no previous experience with humans. The tame kits performed much better at this task than the wild kits did. When dogs were developed from wolves, selection against fear and aggression “may have been sufficient to produce the unusual ability of dogs to use human communicative gestures,” Dr. Hare wrote last year in the journal Current Biology.

1 comment:

xenobiologista said...

(Hi, I don't know you but I was Googling the silver fox experiment and your blog post came up.)

the genes for tameness might have superficial physical as well as behavioral effects.

The other thing I was thinking was that the genes involved in tameness - the relevant neurotransmitter synthesis enzymes, cell adhesion molecules, whatever - might be physically linked to coat colour genes (i.e. the loci are close together on the same chromosomes)? Too lazy to look up if anyone's mapped the fox or dog genomes =)

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