Nice
Rats, Nasty Rats: Maybe It’s All in the Genes
Jan-Peter Boening
for The New York Times
Studying the genetics of
domestication, Dmitri K. Belyaev
developed colonies of silver foxes, river otters and minks, as well as rats,
starting in 1959.
Published:
July 25, 2006
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reader questions about this article. Read his
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Raul Arias
The other colony of rats has been
bred from exactly the same stock, but for aggressiveness instead. These animals
are ferocious. When a visitor appears, the rats hurl themselves screaming
toward their bars.
“Imagine
the most evil supervillain and the nicest, sweetest
cartoon animal, and that’s what these two strains of rat are like,” said
Tecumseh Fitch, an animal behavior expert at the University of St. Andrews in
Scotland who several years ago visited the rats at the farm, about six miles
from Akademgorodok, near the Siberian city of
Novosibirsk. Frank Albert, a graduate student at the Max Planck Institute for
Evolutionary Anthropology in
“The
ferocious rats cannot be handled,” Mr. Albert said. “They will not tolerate it.
They go totally crazy if you try to pick them up.”
When
the aggressive rats have to be moved, Mr. Albert places two cages side by side
with the doors open and lets the rats change cages by themselves.
He is taking care that they do not escape to the sewers of
The
two strains of rat are part of a remarkable experiment started in the former
Belyaev’s brother was exiled to a concentration camp, where he
died, but Belyaev was able to move to Siberia in 1958
and became director of the
Belyaev decided to study the genetics of domestication, a problem
to which
Belyaev’s hypothesis was that all domesticated species had been
selected for a single criterion: tameness. This quality, in his view, had
dragged along with it most of the other features that distinguish domestic
animals from their wild forebears, like droopy ears, patches of white in the
fur and changes in skull shape.
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
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.
The
tame foxes, Dr. Fitch reported, were also “incredibly endearing.” They were
clean and quiet and made excellent house pets, though — being highly active —
they preferred a house with a yard to an apartment. They did not like leashes,
though they tolerated them.
American
researchers have suggested that the foxes be made available as pets, partly to ensure their survival should the
“There was a time when Soviet science was in a
desperate state and Belyaev’s foxes were endangered,”
said Ray Coppinger, a dog biologist at
Jan-Peter Boening for The New York Times
Frank Albert, a graduate
student at the Max Planck Institute for Evolutionary Anthropology in
Ask Science
Nicholas Wade answered select
reader questions about this article. Read his
answers.
Related
Videos
of Fox Behavior (Cornell.edu)
The rats used in Mr. Albert's
research come from an experiment started in the former
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
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.
Dr.
Hare believes that wolves probably have the same cognitive powers as dogs, but
their ability to solve social problems, like picking up human cues to hidden
food, is masked by their fear. Dogs, after their fear is removed by
domestication, see humans as potential social partners, not as predators, and
are ready to interact with them. But though selection for tameness was probably
the first step in domesticating dogs, Dr. Hare said, they may well have adapted
to human societies in other ways, with the smarter dogs leaving more progeny.
Although
most of the tame foxes have stayed in
“It
looked as if it would not work for a long time, but in the end we managed to
build enough trust,” Dr. Paabo said. He and his
student, Mr. Albert, work closely with Dr. Plyusnina.
Mr. Albert hopes to identify which of the rats’ genes were selected for by the
domestication process.
His
strategy is to cross the tame rats with the ferocious rats and then score the
progeny for how much of each trait they inherit. He hopes to identify 200 sites
along the genome at which the tame and ferocious rats differ. If one or more of
the sites correlate with tameness or fierceness in the progeny, they will
probably lie near important genes that underlie one of the two traits.
The
genes, if Mr. Albert finds them, would be of great interest because they are
presumably the same in all species of domesticated mammal. That may even
include humans. Richard Wrangham, a primatologist at Harvard, has
proposed that people are a domesticated form of ape, the domestication having
been self-administered as human societies penalized or ostracized individuals
who were too aggressive.
Dr.
Paabo said that if Mr. Albert identified the genes
responsible for domestication in rats, “we would also look at those genes in
humans and apes to see if they might be involved in human evolution.”
Human
self-domestication, if it occurred, would probably not have exactly the same
genetic basis as tameness in animals. But Mr. Albert said that if he could
pinpoint the genetic difference between the tame and ferocious rats, he would
compare the chimp genome and the human genome to see if they showed a similar
difference.
One
possibility is that a handful of genes — perhaps even just one — underlie all
the changes seen in domestication. A structure in the embryo of all
vertebrates, known as the neural crest, is the source of cells that constitute
much of the face, skull and pigment cells, and many parts of the peripheral
nervous system and endocrine system. If the genes in the neural crest cells
were delayed just a little in coming into action, a whole range of tissues
could be affected, including the maturation of the adrenal glands that underlies
the first fear response of young animals, Dr. Fitch has written.
Could
a single gene that affects the timing of neural crest cell development underlie
the whole phenomenon of animal and human domestication? “There would be one
happy science Ph.D. student if that were true,” Mr. Albert said.