Early Canid Domestication: The Farm-Fox Experiment
Foxes bred for tamability in a 40-year experiment exhibit remarkable transformations that suggest an interplay between behavioral genetics and development
When scientists ponder how animals came to be domesticated, they
almost inevitably wind up thinking about dogs. The dog was probably
the first domestic animal, and it is the one in which domestication
has progressed the furthest—far enough to turn Canis
lupus into Canis familiaris. Evolutionary theorists
have long speculated about exactly how dogs' association with human
beings may have been linked to their divergence from their wild wolf
forebears, a topic that anthropologist Darcy Morey has discussed in
some detail in the pages of this magazine (July–August 1994).
As Morey pointed out, debates about the origins of animal
domestication tend to focus on "the issue of
intentionality"—the extent to which domestication was the
result of deliberate human choice. Was domestication actually
"self-domestication," the colonization of new ecological
niches by animals such as wolves? Or did it result from intentional
decisions by human beings? How you answer those questions will
determine how you understand the morphological and physiological
changes that domestication has brought about—whether as the
results of the pressure of natural selection in a new niche, or as
deliberately cultivated advantageous traits.
In many ways, though, the question of intentionality is beside the
point. Domestication was not a single event but rather a long,
complex process. Natural selection and artificial selection may both
have operated at different times or even at the same time. For
example, even if prehistoric people deliberately set out to
domesticate wolves, natural selection would still have been at work.
The selective regime may have changed drastically when wolves
started living with people, but selective pressure continued
regardless of anything Homo sapiens chose to do.
Another problem with the debate over intentionality is that it can
overshadow other important questions. For example, in becoming
domesticated, animals have undergone a host of changes in
morphology, physiology and behavior. What do those changes have in
common? Do they stem from a single cause, and if so, what is it? In
the case of the dog, Morey identifies one common factor as
pedomorphosis, the retention of juvenile traits by adults.
Those traits include both morphological ones, such as skulls that
are unusually broad for their length, and behavioral ones, such as
whining, barking and submissiveness—all characteristics that
wolves outgrow but that dogs do not. Morey considers pedomorphosis
in dogs a by-product of natural selection for earlier sexual
maturity and smaller body size, features that, according to
evolutionary theory, ought to increase the fitness of animals
engaged in colonizing a new ecological niche.
The common patterns are not confined to a single species. In a wide
range of mammals—herbivores and predators, large and
small— domestication seems to have brought with it strikingly
similar changes in appearance and behavior: changes in size, changes
in coat color, even changes in the animals' reproductive cycles. Our
research group at the Institute of Cytology and Genetics in
Novosibirsk, Siberia, has spent decades investigating such patterns
and other questions of the early evolution of domestic animals. Our
work grew out of the interests and ideas of the late director of our
institute, the geneticist Dmitry K. Belyaev.
Like Morey, Belyaev believed
that the patterns of changes observed in domesticated animals
resulted from genetic changes that occurred in the course of
selection. Belyaev, however, believed that the key factor selected
for was not size or reproduction, but behavior—specifically
amenability to domestication, or tamability. More than any
other quality, Belyaev believed, tamability must have determined how
well an animal would adapt to life among human beings. Because
behavior is rooted in biology, selecting for tameness and against
aggression means selecting for physiological changes in the systems
that govern the body's hormones and neurochemicals. Those changes,
in turn, could have had far-reaching effects on the development of
the animals themselves, effects that might well explain why
different animals would respond in similar ways when subjected to
the same kinds of selective pressures.
To test his hypothesis, Belyaev decided to turn back the clock to
the point at which animals received the first challenge of
domestication. By replaying the process, he would be able to see how
changes in behavior, physiology and morphology first came about. Of
course, reproducing the ways and means of those ancient
transformations, even in the roughest outlines, would be a
formidable task. To keep things as clear and simple as possible,
Belyaev designed a selective-breeding program to reproduce a single
major factor, strong selection pressure for tamability. He chose as
his experimental model a species taxonomically close to the dog but
never before domesticated: Vulpes vulpes, the silver fox.
Belyaev's fox-breeding experiment occupied the last 26 years of his
life. Today, 14 years after his death, it is still in progress.
Through genetic selection alone, our research group has created a
population of tame foxes fundamentally different in temperament and
behavior from their wild forebears. In the process we have observed
some striking changes in physiology, morphology and behavior, which
mirror the changes known in other domestic animals and bear out many
of Belyaev's ideas.