Authors:
Source:
Nicholls, Henry
New Scientist; 10/3/2009, Vol. 204 Issue 2728, p40-43, 4p
Document Type:
Article
Subject Terms:
*ANIMAL behavior
*PHYSIOLOGY
*ANIMAL genetics
*BEHAVIOR genetics
*BEHAVIOR disorders
Abstract:
The article discusses studies on the genetics responsible for the behavioural differences of animals. It
states that the genetic basis of tameness will help us understand what makes some people aggressive
and will possibly lead to treatments for behavioural disorders. Results of investigations into the animals'
physiology are discussed. Also cited are studies by geneticist Svante Pääbo and by geneticist Dmitry
Belyaev.
Full Text Word Count:
2337
ISSN:
02624079
Accession Number:
44605844
Database:
Academic Source Premier
The Secret to Taming Animals
Section: Features
Thanks to some extraordinary experiments conducted in Russia, we are about to find out what makes animals - perhaps
including us - tame or aggressive
IN 2003, while geneticist Svante Pääbo was visiting Novosibirsk, Russia's third-largest city, he decided to look in on a
famous experiment run by the Institute of Cytology and Genetics, which is based in the city. Fifty years ago, the then head of
the IC&G, geneticist Dmitry Belyaev, had begun breeding silver foxes to see how easily they could be tamed. What Pääbo
didn't know, though, is that Belyaev had also set up another experiment in the 1970s involving rats. This time, one line of rats
was selected for tameness and another selected for aggression.
When Pääbo saw them, he was stunned. After just 30 years of selection, the IC&G researchers had fashioned two
populations that could hardly be more different. "I could take the tame ones out of the cage with my bare hands. They would
creep under my shirt and seemed to actually seek and enjoy contact," recalls Pääbo. "The aggressive animals were so
aggressive I got the feeling that 10 or 20 of them would probably kill me if they got out of the cages."
Here was a great opportunity to uncover the genetic changes responsible for the behavioural differences, Pääbo realised.
Back at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, Pääbo and his team have been trying to
do just this. If they succeed, their findings could have far-reaching consequences.
The zebra, for instance, is a stubborn beast, one that has thwarted all efforts to domesticate it, as have the cheetah, the
African buffalo and the rhinoceros. Understanding the genetic basis of tameness might make it possible to domesticate the
undomesticatable and turn exotic species into farm animals or even pets. It could also help us understand what makes some
people overly aggressive - and perhaps even lead to treatments for behavioural disorders.
Most domesticated mammals are really rather different from their wild ancestors: they often have a radically different body
shape, frequently sport unusual fur patterns or markings, and it is not uncommon for them to be able to breed all year round.
Surely it must have taken many, many generations for all these differences to accumulate?
Charles Darwin certainly thought so, suggesting the process of domestication was "insensibly slow". But Belyaev thought
otherwise. He proposed that many of the features typical of domesticates arose because our distant human ancestors made
their initial selection of wild animals on the basis of just one, rather practical characteristic: tameness. If this were the case,
domestication was not only simple, it might also have taken far fewer generations than imagined.
A simple thought experiment will give an idea of how Belyaev probably saw things. Imagine yourself back some 10,000
years. You've been hunting and gathering for as long as you can remember, and quite frankly you're sick of it. There, on the
horizon, is a herd of herbivores. Wouldn't it be nice, you think, if you could keep and breed a few close to home? You'd have
ready access to meat and milk all year round. Life would be so much easier.
You slowly approach the herd. The skittish animals stamp and back off. The unflustered ones blink and stay their ground.
The upshot is that the animals you end up taking home are the ones that are least perturbed by human company. If this
behavioural trait has a genetic basis, you have already selected animals boasting genes for tameness. That, the bold
Russian hypothesised, is a crucial step in domestication. All the other stuff that characterises most domesticated mammals the floppy ears, varied coat markings and altered reproduction - are simply by-products of selecting for tameness.
In 1959, Belyaev set out to test his idea. He obtained 130 relatively friendly silver foxes from a fur farm in Estonia and
installed them at a farm near the small town of Kainskaya Zaimka, on the outskirts of Novosibirsk. He began to breed them,
but in each generation only allowed the very tamest animals to reproduce. Within four generations, some of the foxes had
started to wag their tails; after eight generations new spots and markings began to appear on some of the offspring; then
ears flopped, tails shortened, skulls widened and the foxes became more relaxed about when they bred. After just 20 years,
Belyaev's team had created a domestic fox.
Further investigations into the animals' physiology were revealing. Compared with wild silver foxes, the tame foxes have
reduced activity of the hypothalamic-pituitary-adrenal axis, a complex set of nervous and hormonal signals that, among other
things, controls an animal's response to stress. Tame foxes also have higher levels in their brains of serotonin, a
neurotransmitter that inhibits aggressive behaviour. These and other subtle modifications go some way to explaining why the
tame foxes are so chilled-out.
The silver fox is just one animal, though. Would selection for tameness bring about similar rapid changes in other mammals,
too? It was to address this that Belyaev obtained a group of wild rats in 1972 and set about creating the two lineages.
Next, Belyaev turned his attention to American mink. He approached a fur farm housing 30,000 animals and came away with
200 relatively tame individuals. After just four generations of selective breeding, there was clear evidence that domestication
was under way. Not only were the animals easier to approach, but novel coat colours and other anatomical features had
started to appear, just as they had done with the foxes.
Tame otters
Starting in 1980, the researchers began to capture wild river otters, bringing them to the farm from Sakhalin Island, north of
Japan. Thirteen years and three generations later, the percentage of tame river otters at the farm had more than tripled, from
around 10 per cent initially. These animals also boasted lighter markings, earlier reproduction and changes in brain
chemistry.
The results of these experiments suggest that Belyaev was right: far from the characteristic features of domesticated
mammals requiring hundreds of generations of selective breeding, they start to appear in just a few. With all the animals,
selecting for tameness brought with it new colour variants and altered reproduction, in fact pretty much all the features typical
of a domesticated species. According to Lyudmila Trut, who took charge of the experiments after Belyaev's death in 1985,
part of the reason is that breeding for tameness produces changes in the timing of developmental processes.
With the break-up of the Soviet Union in the early 1990s, these ground-breaking experiments ran into difficulty. By the end of
the decade, with little money for food or salaries, the IC&G was forced to reduce the number of breeding foxes from 700 to
just 100 and the number of mink from over 6000 to around 1000. The otter programme did not survive the funding crisis,
though some of the tame animals and their descendants can still be seen at Moscow Zoo.
Things began to look up after Pääbo came to see the foxes. After some negotiation, Trut agreed to establish colonies of
tame and aggressive rats in Germany to allow the genetic changes in the animals to be identified. "It took over a year to get
everything in place," says Pääbo. When, in late 2005, 15 tame and 15 aggressive rats left Novosibirsk, they were
chaperoned all the way to Leipzig by IC&G staff.
One of the first things the team in Germany did was to check that the differences in the rats' behaviour really are due to
nature, not nurture. To do this, they swapped the offspring shortly after birth, so pups born of tame parents were being
reared by aggressive mothers and vice versa. If the post-natal environment has an influence, aggressive pups reared by
tame mothers would become tamer. "We did not see that at all," says Frank Albert, who led the study (Hormones and
Behaviour, vol 53, p 413). The cross-fostered rats behaved exactly like their genetic parents, he says.
There is still the possibility that the hormones sloshing around during pregnancy might alter fetal development and hence
behaviour. Ruling this out requires switching embryos between mothers, which has yet to be done in rats. It has, however,
been done in the silver foxes and had no obvious effect.
So, confident that the differences in behaviour are down to gene variants, the researchers set out to find them. They could
not simply compare the DNA of the tame and aggressive strains, since many of the differences would have nothing to do with
their behaviour - any two populations kept apart will diverge genetically even without selection, due to random mutations.
Instead, they cross-bred the rats. The second generation of hybrids had a spectrum of behaviour from exceedingly tame to
monstrously aggressive.
The next task was to measure tameness, for which they used the "glove test". Wearing two cotton gloves and a third made
from chain mail, a researcher moves his or her hand slowly towards the rat, attempts to touch it and pick it up. "You can do
anything with the tame rats," says Albert. "You can touch them, you can pick them up, you can move them around, you can
move their arms and legs." The chain mail is there for the aggressive rats. "The moment you open the cage door some of
them will come flying at the glove, bite it, latch on and scream," he says. "After testing you sometimes have bruises on your
fingers."
Each glove test is videoed, so researchers who have no direct contact with the rats can objectively rate how tame or
aggressive they are. The team then compared the behavioural scores with 200 genetic markers. Their preliminary findings,
published in June this year (Genetics, vol 182, p 541), highlight several key regions of the genome that have a strong effect
on tameness. "There are at least five genes, probably more, that are having a very complex interaction," says Albert.
The mission is now to home in on what these genes are and exactly what they do. If there are multiple mutations, each with
a small effect on behaviour, this will be pretty challenging, says Leif Andersson, a geneticist at Uppsala University in Sweden
involved in the project. "However, one of our loci has a major effect and influences both behaviour and the size of the adrenal
gland," he says. "I am optimistic that we will be able to reveal the mutation and the gene underlying this major effect within a
couple of years."
Network of genes
Given enough time, more painstaking work and a bit of luck, it seems likely the researchers will identify the entire network of
genes responsible for tameness and aggression in rats. "Once we have them, we will of course see if the same genes and
the same physiological pathways differentiate domesticated animals from their wild relatives," says Albert. "It might be a
general thing."
Indeed, the same genes might turn out to underlie social behaviour in a wide range of mammals - including us (see "The
tame ape"). Trut sees many similarities between the silver foxes and humans, for instance. "The range of behaviours in these
foxes has significant parallels to that of normal and disordered patterns of human sociability," she says. She hopes
pharmaceutical companies will start using the silver foxes to investigate potential therapies for behavioural problems. Selling
the foxes as pets could be another potential source of income for the struggling IC&G. According to Trut, they make good
pets, as devoted as dogs but as independent as cats.
If there is a common genetic basis for domestication, the work of Pääbo and Albert could make it much easier to domesticate
other species. Take the African buffalo, for example. It is notoriously aggressive, killing more people each year than lions.
The benefits of creating a line of less volatile - even friendly - buffalo would be enormous. As these animals are well adapted
to local conditions, they would make for a more robust herd than domesticated cattle. Domesticating them might simply be a
question of screening buffalo to find some with the right genes, and setting up some suitable pairings. If this failed, there
would be the prospect of tinkering more directly with the African buffalo genome.
Some people will object to the very notion of domesticating more wild species, whether for farms or as pets. But many tame
animals, such as dogs, cats, horses, sheep, now far outnumber their wild relatives. Wouldn't it be better if some threatened
animals survived as pets or farm animals rather than not at all?
There is also a certain appeal to the idea of taming exotic creatures. Take zebras. While a few individuals have managed to
ride them, they have never been fully tamed. "Maybe we have not tried hard enough to find zebras that are suitable for
domestication," suggests Andersson. If Pääbo's genetic quest reveals the secret to taming the zebra, Royal Ascot might
never be the same again.
The tame ape Henry Nicholls
Perhaps we are also a product of domestication. Over the last 30,000 years, human brain size, tooth size and jaw size have
all been on the decrease - exactly the same kind of changes that have occurred as animals such as dogs were
domesticated, says Richard Wrangham, a biological anthropologist at Harvard University. This raises the intriguing possibility
that humans have been on an evolutionary journey from aggressive chimpanzee-like ancestor to the relatively tame species
we are today.
If this is the case, who did the domesticating? The answer, suggests Wrangham, is that we did. Humans, he argues, are
"self-domesticated apes", with natural selection favouring individuals that showed tame and cooperative behaviour, and
weeding out the more aggressive and antagonistic among us.
~~~~~~~~
By Henry Nicholls
Henry Nicholls is a science journalist based in London. He is writing Political Animal, a book about pandas and China to be
published by Profile in 2010