Dogs first snuggled up with people in Central Asia. That’s the conclusion of a new study looking at genetic diversity in these popular pets. Earlier findings had suggested dogs were first tamed elsewhere.
Laura Shannon works at Cornell University in Ithaca, N.Y. As an evolutionary geneticist, she studies how traits in a species have changed over enormous spans of time. For the new study, Shannon joined an international team. “We have a large dataset,” she says, which allowed their team “to sample dogs from all over the world.”
In all, they looked at DNA from nearly 5,000 dogs. Most were purebreds. But more than 500 were free-roaming dogs living in villages around the world. Such “village dogs” make up the majority of dogs worldwide.
Dogs from Central Asia harbored the greatest diversity in their genes. “As you move out from Central Asia, we see a decrease in diversity,” Shannon says. That suggests people must have begun taming wild canines into pets near to lands now known as Nepal and Mongolia.
The researchers shared their findings October 19 in the Proceedings of the National Academy of Sciences.
Some genes in a starting species will be lost as animals are tamed, Shannon explains. Why? Only a fraction of the original group of tamed — or domesticated — dogs would have moved along with people to new areas. These dogs would have possessed just some of the genes present in the dogs they had left behind. Similar to how the neck on a soda bottle restricts the amount of liquid that gets through, the frontier dogs would bring only some of their community’s genes with them into a new area.
Earlier research had suggested that dog domestication occurred in a host of places. These included Europe, the Middle East, China, Siberia and North Africa. But many of these studies examined a limited type of genes. For instance, some looked at those in mitochondrial (My-tow-KON-dree-ul) DNA. These are genes that can be inherited only from the mother. Others looked only at the genes present as part of the Y chromosome that males get from their dads. Still other studies may have focused on autosomal (Aw-tow-SOAM-ul) DNA. This type holds genes other than those on sex chromosomes (the X or Y types).
The new study considered genes from each type of DNA, Shannon says. “That let us get the most complete picture we could.”
But these data all came from living animals. A lack of ancient DNA has led some critics to question the new study’s conclusions. Robert Wayne of the University of California, Los Angeles, is among them. Wayne, an evolutionary biologist, is concerned that this study’s findings don’t match up with those from earlier ones. Moreover, he argues that diversity patterns in living dogs might not be a foolproof map of domestication events in ancient times.
Ancient DNA could provide more insight into where wild canines were first tamed into dogs, Shannon agrees. Still, she believes, the new study will add to a global effort using many genetic techniques to investigate where the efforts to domesticate dogs and wolves first took hold.
Studying domestication patterns adds to the human story, too, she says. “Studying the history of organisms that we use and breed, and that we’ve had an effect on, tells us about history as well as culture and human migration.”
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autosomal DNA The DNA found in a cell’s nucleus and housed in all but the sex chromosomes.
canid The biological family of mammals that are carnivores and omnivores. The family includes dogs, wolves, foxes, jackals and coyotes. Members of this family are known as canines.
chromosome A single threadlike piece of coiled DNA found in a cell’s nucleus. A chromosome is generally X-shaped in animals and plants. Some segments of DNA in a chromosome are genes. Other segments of DNA in a chromosome are landing pads for proteins. The function of other segments of DNA in chromosomes is still not fully understood by scientists.
culture (in social science) The sum total of typical behaviors and social practices of a related group of people (such as a tribe or nation). A culture includes their beliefs, values, and the symbols that they accept and or use. It’s passed on from generation to generation through learning. Once thought to be exclusive to humans, scientists have recognized signs of culture in several other animal species, including dolphins and primates.
data Facts and/or statistics collected together for analysis but not necessarily organized in a way that give them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.
data set (or dataset) A large, discrete group of data collected or assembled for a particular purpose.
diversity (in biology) A range of different life forms.
DNA (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
domestication A process of producing a tame version of an animal from a wild one, which can take thousands of years.
evolutionary biologist Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).
evolutionary genetics A field of biology that focuses on how genes — and the traits they lead to — change over long periods of time (potentially over millennia or more). People who work in this field are known as evolutionary geneticists.
gene (adj. genetic) A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
mitochondria (sing. mitochondrion) A structure in all cells (except bacteria) found outside of their nuclei. Here the cell breaks down nutrients and converts them into a form of energy known as ATP.
mitochondrial DNA DNA passed on offspring from their female parent. Housed in mitochrondria, this DNA is double-stranded but circular. It’s also very small, only possessing a small share of the genes found in the main package of DNA, the material found in a cell’s nucleus.
Proceedings of the National Academy of Sciences A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of he more than 3,000 papers published each year, now, is not only peer reviewed, but also approved by a member of the U.S. National Academy of Sciences.
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Learn more about mitochrondrial DNA here, from the National Institutes of Health.
Original Journal Source: L. Shannon et al. Genetic structure in village dogs reveals a Central Asian domestication origin. Proceedings of the National Academy of Sciences. Published online October 19, 2015. doi: 10.1073/pnas.1516215112.