Evolution of dogs
There are more than 400 pure breeds of dogs in the world and many other mixed breed dogs. They share many common behaviors and habits, but they also look very different from each other. That raises an interesting question: “Do the Chihuahua and Great Dane come from the same ancestry?” The answer is YES! All the pure breed dogs and mutts come from one common ancestry, gray wolf, which first appeared about 1 million years ago in Eurasia. Dogs were domesticated from gray wolf around 15,000 years ago. The fossilized remains of a 33,000-year-old dog-like animal, found in the 1970s in southern Siberia's Altay Mountains, is the earliest well-preserved dog-like animal. Dog-like fossils dating from 12,000-11,000 years BP have been found buried alongside humans in Israel(Davis and Valla, 1978; Ovodov et al., 2011). However, the problem of the fossil study is that we can hardly know whether the fossil belongs to a dog or wolf based on their skulls and shapes. These evidences can only suggest a roughly timeline of this evolution process, we need more evidence to make the conclusion. Genomic information indicates that dog domestication started at least 10,000 years ago in southern East Asia or the Middle East. It is unclear that where, why and how dogs were first domesticated. A famous argument is that wolves have scavenged around human settlements and domesticated themselves. This process could occurred in any area where both wolves and human lived, and from hundreds of thousands of years ago to the present(Clutton-Brock et al., 2017).
Difference between wolves and dogs
There are many differences between modern dogs and gray wolf ancestors. These include reduced aggressiveness and altered social cognition capabilities. Dogs also differ physically from wolves, showing floppy ears, various coat colors, and curled tails(Clutton-Brock et al., 2017). A study published in Nature, a scientific journal, in 2013 compared the genome between wolves and domesticated dogs, and found 36 genomic regions differ between them. These parts of the genome contain many genes involved in brain function and the nervous system. Interestly, the regions also contain many genes involved in starch digestion and fat metabolism(Axelsson et al., 2013). It’s possible that increased starch digestion function provides ancient domesticated dogs with a better chance to survive. An increased capacity for digesting starches, which are found in grains and other foods from plants, would certainly help dogs to make good use of foods shared by humans. Even we are able to find the genomic difference, we still don’t know what genes drove the evolution from wolf to dogs, what genes are the most crucial causes.
photo credit: https://en.wikipedia.org/wiki/Origin_of_the_domestic_dog
Artificial design of dogs: Breeding
During the past 200 years, selective breeding by humans has resulted in the artificial "evolution" of the dog into many different types. There are now over 400 dog breeds all over the world, and they drastically vary in shapes and sizes. Some dogs are bred for their abilities to help humans. For example, Border Collies are selected to protect flocks because of their sagacity, intelligence, and trainability. In addition, the Labrador Retriever was bred to be both a friendly companion and a useful working dog breed. Some dogs are bred just for their physical characteristics. Like the Chihuahua, who’s adorable big head and small body size is favored by many pet owners. Dogs have large range of body sizes, the Great Dane is one of the largest breeds, and it usually weighs around 100-120 pounds. Chihuahua, the smallest breed of dogs, only weighs around 4-6 pounds. In 2010, the Bustamante group at Stanford University found that variation in just six places of the dog genome can explain about 80 of the variation in height and weight among dog breeds(Boyko et al., 2010). With so many studies have been done and so many controversies have been come up, we still have a long way to go to find out those ‘hidden’ truth. With the development of sequencing technology, we are able to sequence every dog and wolf to find out what their DNA looks like. However, the problem is we don’t really know what the difference stands for, one single gene with large effect made the evolution happen or many genes with minor effect worked together to drive this evolution from wolf to dog? We don’t know the answer yet, but with all the advanced technology and all the help from people who are interested in science, we will get there one day!
Axelsson, E., Ratnakumar, A., Arendt, M.L., and Maqbool, K. (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature.
Boyko, A.R., Quignon, P., Li, L., Schoenebeck, J.J., Degenhardt, J.D., Lohmueller, K.E., Zhao, K., Brisbin, A., Parker, H.G., vonHoldt, B.M., et al. (2010). A Simple Genetic Architecture Underlies Morphological Variation in Dogs. PLoS Biol. 8, e1000451.
Clutton-Brock, J., vonHoldt, B.M., Lord, K., and van den Berg, L, et al. (2017). The Domestic Dog.
Davis, S.J.M., and Valla, F.R. (1978). Evidence for domestication of the dog 12,000 years ago in the Natufian of Israel. Nature.
Ovodov, N.D., Crockford, S.J., Kuzmin, Y.V., Higham, T.F.G., Hodgins, G.W.L., and van der Plicht, J. (2011). A 33,000-Year-Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum. PLoS One 6, e22821.