Why don’t we have pet lions? Why do we raise cows and pigs for food, but not hippopotamuses or moose? How did animals as physically diverse as bulldogs, greyhounds and chihuahuas all originate from wolves?
These questions may sound elementary, but all have incredibly complex answers that may be found somewhere in the realm of behavioral genetics, a field of study that examines the role of genetics in human and animal behavior. This highly interdisciplinary field draws on elements of biology, statistics, psychology and even history, and is often associated with the “nature versus nurture” debate. For the purposes of this case history, we’ll be focusing on animals, and specifically on their domestication.
Mapping the constellation of traits that determine domestication is one of the leading questions in animal behavioral genetics. Domestication is the process through which animal populations are selected at the genetic level to display traits that benefit humans in some way. It differs from taming, which is simply a process of animals becoming accustomed to human presence,in that changes in the genetics, physiology, and behavior of the animal all occur. According to the Convention on Biological Diversity, a domesticated species is defined as a “species in which the evolutionary process has been influenced by humans to meet their needs” (Convention).
In the 1950s, a group of Russian scientists led by Dmitri Belyaev set out to investigate the origins of domestication in an animal that had never been selectively bred for it before: the silver variant of the red fox,Vulpes vulpes. His team spent decades breeding silver foxes, starting with a population of animals that showed the least fear of humans and then breeding only the individuals who responded most positively to people. More than half a century later, Belyaev’s team now manages a population of foxes whose behavior and appearance has dramatically changed (Trut).
You can see the results of the Belyaev fox experiment in the Youtube video below. The first foxes in the video are a group that has been deliberately bred to contrast the domesticated group – these “minus” foxes show extreme hostility towards humans. The “plus” foxes, animals selected for tameness and affection, can be found at 1:55. Note that their behavior is dramatically different from both the “minus” foxes and even that of a control group – these animals actually seek out human contact, wagging their tails and licking their handlers to show affection. Intriguingly, these animals display different physical characteristics as well – a wider range of coat colors, white patterning, floppy ears and curly tails – all traits typically associated with domestic dogs.
Though the results of the Belyaev project are quite obvious, the actual mechanisms of how these behaviors were achieved remain something of a mystery. The expression of genetic traits is notoriously hard to predict. A “master suite” of genes present in all animals and responsible for the shared, domestic characteristics would be the holy grail of domestication studies. The idea of a domestication gene has been explored by a number of scientists, but the challenge of identifying such a gene or genes, should they exist, is formidable. Even if domestication is the result of only a few changes in an animal’s genetic makeup, the range of behavioral and physical differences that can be observed between wild and domesticated animals is so vast that locating the genetic source of these changes seems nearly impossible. As authors K. Dobney and G. Larson point out, “The cascade initiated by those few genes is likely to be so complex that identifying the highest level ‘domestication genes’ becomes, at best, highly problematic” (Dobney and Larson).
Even high-tech gene alteration procedures yield frustrating and often baffling results. In “knockout” experiments, for example, specific genes are chemically prevented from performing their normal functions. The knockout experiments have shown that blocking different genes can have unexpected effects on behavior. In a series of these trials performed on mice, researchers deactivated genes involved with learning. The result was a group of super-aggressive mice that showed little to no fear response and would fight until they died of exertion. Another experiment deactivated the gene that produces enkephalin, a brain opiate involved in pain perception. These mutant mice unexpectedly had a heightened sensitivity to noise and demonstrated extreme anxiety (Grandin and Deesing).
“The bottom line conclusion from several different knockout experiments is that changing one gene has unexpected effects on other systems,” writes Temple Grandin, a renowned animal behavior expert. “Traits are linked, and it may be impossible to completely isolate single gene effects. Researchers warn that one must be careful not to jump to a conclusion that they have found an “aggression gene” or a “maternal gene” or an “anxiety gene.” To use an engineering analogy, one would not conclude that they had found the “picture center” in a television set after they cut one circuit inside the set that ruined the picture” (Grandin and Deesing).
To confuse matters further, behavioral genetics currently cannot determine how much of an impact humans had on the process of creating the domestic animals we know today. Emerging historical evidence suggests that domesticated animals actually helped tame themselves, adjusting to life around humans long before people actively took part in any sort of genetic selection. According to Greger Larson, an expert on genetics and domestication at Durham University in the United Kingdom, most early animals like dogs, pigs, and assorted ungulates were probably managed unintentionally by humans long before they became domesticated in any traditional sense. Domestication “implies something top down, something that humans did intentionally,” he says. “But the complex story is so much more interesting” (Ratliff).
As with many other fields of scientific inquiry, behavioral genetics raises a dozen new questions for every one it answers. A definitive answer to any of these will have powerful implications across the board – after all, human behavior has both shaped and been shaped by the presence of domesticated animals since before the dawn of agriculture. To understand domestication and behavioral genetics is to understand more of human history, a concept that continues to capture the imaginations of scientists and non-scientists alike. With a world of knowledge left to be discovered in behavioral genetics, perhaps one day we’ll get to have those pet lions after all.
Dobney, K., and G. Larson. “Genetics and animal domestication: new windows on an elusive process.”Journal of Zoology. 29.2 (2006): n. page. Web. 25 Sep. 2012.
Domesticated Fox Experiment. Dir. iCyFlaMeZ96. Youtube, Film. 24 Sep 2012. <http://www.youtube.com/watch?v=-L58NPPQ5eI>.
Grandin, Temple, and Mark Deesing.Genetics and the Behavior of Domestic Animals. San Diego: Acedemic Press, 1998. Web.<http://www.grandin.com/references/genetics.html>.
International.Convention on Biological Diversity. 1992. Web. <http://www.cbd.int/>.
Ratliff, Evan. “Taming The Wild.”National Geographic. March 2011: n. page. Web. 24 Sep. 2012.
Trut, Lyudmila. “Early Canid Domestication: The Farm-Fox Experiment.”American Scientist. 87.March-April (1999): n. page. Web. 25 Sep. 2012.