Evolution of Domesticated Dogs (Canis Lupis familiaris)
The first Canids were the evident in the Eocene period (40 to 35 million years ago) (Strauss, 2013). The Hesperocyon is believed to be the direct ancestor to all later caninds. The Hesperocyon was about the size of small fox and has the same inner ear structure of later dogs (Strauss, 2013). The fossil records shows that the Hesperocyon could be one of the most common animals in prehistoric North America because of the abundance of fossils found (Wang, 1994; Lloyd & Eberle, 2012). The Leptocyon is a distant relative to the Hesperocyon and was believed to be similar in size (Mestel, 1994). Its direct descendant, Eucyon, was able to use the Bering land bridge to cross into North America and spread to different continents (Strauss, 2013; Lyras & Vandergeer, 2003 ). It is estimated that humans first began domesticating Gray Wolves (Canis lupus) anywhere from 30,000 to 14,000 years ago (Ovodov; et. al., 2011). It is difficult to determine where the change from Gray Wolf to domesticated dog takes place, but scientists rely on morphological characteristics as DNA analyses has had mixed results (Ovodov; et. al., 2011). The remains of early dogs in human graves can also give certain time frames for the domestication of dogs (Ovodov; et. al., 2011).
Although it has been assumed that early humans stole wolf pups to domesticate, wolves may have domesticated themselves. Wolves may have been attracted to dumps created by the more sedentary life of first farmers. Studies reveal that dogs have three genes – AMY2B, MGAM and SGLT1 – that allow them to digest and obtain nutrients from a starch-rich diet, allowing them to thrive off of the food they scavenged (Axelsson, 2013). Additionally, the wolves that remained close to human settlements would have exhibited higher levels of tolerance for humans, or tameness, than their wild counterparts. This theory is supported by studies showing a difference in gene expression in the brain of domesticated and wild canines. Modern domesticated dogs have unique behaviors and interactions with human, such as the ability to follow human signals that their wild counterparts do not demonstrate (Li, 2013).
The dog (Canis lupus familiaris) has been a companion of man for the last 14,000 years as the oldest domesticated animal (Ovodov, et. al., 2011). The World Canine Organization currently recognizes over 400 different breeds of dogs that can be placed into 10 categories, Sheepdogs and Cattle dogs, Pincher and Schnauzer, Terriers, Dachshunds, Spitz and Primitive types, Scent hounds, Pointers and Setters, Retrievers, Toy dogs, and Sight hounds (Coren, 2013; Streitberger; et. al., 2012). These subgroupings do not take into account the crossbreeds of dogs as well. Charles Darwin used domesticated dogs as examples of artificial selection, because humans helped to design their differences (Pojeta & Springer, N.D.) Certain dogs were bred to highlight specific characteristics (Careau; et. al., 2010). This breeding process has occurred over the past 150 years, to create the above mentioned categories (Steightberger; et. al., 2012). These classifications have been created based on geographic locations, morphology, and intended purpose of the breeds (Streitberger; et. al., 2012). As humans continue to breed different purebred dogs, a new subgrouping of dogs can be created within a few generations (Steitberger; et. al., 2012).
Diet and Evolution of Domesticated Dogs
A recent study has suggested that diet also helped to shape the evolution of domesticated dogs. Current domesticated dogs consume a more varied diet than their ancestor, the wolf. This genetic change is also paralleled with that of human evolution. Through gentic testing, dogs were shown to have genes for digesting starches; 4-30 copies, where wolves only have 2 copies of the gene. Starches are the primary nutrient in grains such as wheat and rice. Scientists believe that this evolution is connected to wolves that associated themselves with human settlers as they were beginning to farm (Pennisi, 2013).
Moscow's Stray Dogs Evolving Greater Intelligence, Including a Mastery of the Subway
Here is a case of domesticated dogs evolving in different ways as shown in a study conducted on Moscow's stray dogs over the last 30 years. Andrei Poyarkov, a researcher at the A.N. Severtsov Institute of Ecology and Evolution, has seen evolutionary changes in stray dogs that are must contend with the pressure of urban living. This pressure has changed these stray dogs to evolve wolf-like traits, increased intelligence, and even the ability to use Moscow's subway system.
Poyarkov found basically four categories of dogs which operate in different ecological niches which he calls: guard dogs, scavengers, wild dogs, and beggars. It's the last cateogry, the beggars, that have become adept at begging food fromm commuters and learning to use the subway system, "Using scents, and the ability to recognize the train conductor's names for different stops, they incorporate many stations into their territories", writes Stuart Fox of Popular Science magazine (2010).
Axelsson, E., Ratnakumar, A., Arendt, M., Maqbool, K., Webster, M., Perloski, M., & ... Lindblad-Toh, K. (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature, 495(7441), 360-364
Careau, V., Réale, D., Humphries, M. M., & Thomas, D. W. (2010). The Pace of Life under Artificial Selection: Personality, Energy Expenditure, and Longevity Are Correlated in Domestic Dogs. American Naturalist, 175(6), 754-758. doi:10.1086/652435
Coren, S. (2013, May 23). How many breeds of dogs are there in the world? Retrieved from https://www.psychologytoday.com/blog/canine-corner/201305/how-many-breeds-dogs-are-there-in-the-world
Lloyd, K. J., & Eberle, J. J. (2012). A late Eocene (Chadronian) mammalian fauna from the White River Formation in Kings Canyon, northern Colorado. Rocky Mountain Geology, 47(2), 113-132.
Li, Y., vonHoldt, B., Reynolds, A., Boyko, A., Wayne, R., Wu, D., & Zhang, Y. (2013). Artificial Selection on Brain-Expressed Genes during the Domestication of Dog. Molecular Biology And Evolution, 30(8), 1867-1876
Lyras, G. A., & Vandergeer, A. E. (2003). External brain anatomy in relation to the phylogeny of Caninae (Carnivora: Canidae). Zoological Journal Of The Linnean Society, 138(4), 505-522. doi:10.1046/j.1096-3642.2003.00067.x
Mestel, R. (1994, October 1). Ascent of the dog. Retrieved from http://discovermagazine.com/1994/oct/ascentofthedog434
Ovodov, N. D., Crockford, S. J., Kuzmin, Y. V., Higham, T. G., Hodgins, G. L., & 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(7), 1-7. doi:10.1371/journal.pone.0022821
Pennisi, E. (2013, Jan 23). Diet shaped dog domestication. Retrieved from http://news.sciencemag.org/plants-animals/2013/01/diet-shaped-dog-domestication
Pojeta, J., & Springer, D. (N.D.). Darwin's revolutionary theory. Retrieved from http://www.agiweb.org/news/evolution/darwinstheory.html
Strauss, B. (2013). Prehistoric dogs - the story of dog evolution. Retrieved from https://dinosaurs.about.com/od/otherprehistoriclife/a/Prehistoric-Dogs-The-Story-Of-Dog-Evolution.htm
Streightberger, K.K., Schweizer, M.M., Kropatsch, R.R., Dekomien, G.G., Distl, O.O., Fischer, M.S., & Hertwig, S.T. (2012). Rapid genetic diversitifcation within dog breeds as evidenced by a case study on Schnauzers. Animal Genetics, 43(5), 577-586. doi:10.1111/j.1365-2052.2011.02300.x
Wang, X. (1994), Phylogenetic systematics of the Hesperocyoninae (Carnivora: Canidae). American Museum of Natural History Bulleti. (221) 207 p.