In prehistory, our ancestors' ability to tame the wolves that eventually became dogs may have been due in large part to a canine's willingness to trade meat for potatoes.
Wolves started becoming companions of early humans more than 10,000 years ago, but researchers are still unsure exactly how they were first domesticated. One prominent theory is that the relationship began when wolves started hanging around human settlements to scavenge leftovers from trash heaps.
An international group of researchers decided to investigate the origins of man's best friend by comparing the genomes of 60 dogs and 12 wolves. Discovering how dog genomes differ from those of wolves, and finding where genetic variations are shared among all dog breeds, could point to traits related to domestication.
In a paper in the journal Nature on Wednesday, the scientists said they identified 36 genomic regions that underwent some kind of selective pressure during the process of domestication. Nineteen of the regions are involved in brain function, which could govern behavioral changes that differentiate a tame dog from a wild wolf. But the more novel finding was that 10 of the genetic regions that received this selective pressure are involved in digesting starches and fats.
“Our results show that it was crucial for the survival of early dogs to be able to live on food that largely consisted of vegetables, such as root vegetables and cereals,” lead author and Uppsala University researcher Erik Axelsson said in a statement Wednesday. “This in turn indicates that the domestication of dogs may be connected to the human development of agriculture, and that it was on the scrap heaps of early settlements that the first steps of the development of dogs took place.”
All of the dogs that the researchers studied had significant changes to the genomes that affect all parts of the process of digesting starches, including breaking down complex carbohydrates into simple sugars and transporting that glucose into the bloodstream.
For instance, the team found that dogs carry many more copies of the gene for amylase, an enzyme that kick-starts the first step of starch digestion, than wolves. The gene involved in the next step, converting the sugar maltose into the simpler sugar glucose, turns out to be 12 times more active in dogs than in wolves. Dogs also have very specific alterations in a third gene, which is involved in moving glucose out into the bloodstream, that enhance the efficiency of the process.
This adaptation to carb-rich diets is also found in human evolutionary history, underscoring how dog domestication mirrors our own development. By studying dogs, we might also gain some insight into how our diet changes as a species tie into disease.
Still, the find doesn't quite close the book on dog domestication origins. Humans only started adopting agriculture about 10,000 years ago, and we may have tamed dogs before adopting the farming lifestyle.
UCLA evolutionary biologist Robert Wayne, unaffiliated with the current study, told the Los Angeles Times that dogs might have started out as wolves, hanging around the carcasses of animals killed by our hunter-gatherer ancestors. Then, the starch-tolerant changes might have arisen in the dog genome as they, along with their new masters, adopted a more agrarian diet.
SOURCE: Axelsson et al. “The genomic signature of dog domestication reveals adaptation to a starch-rich diet.” Nature published online 23 January 2013.
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