Who Helped the Dogs Evolve, Who Who?

Contributed by Aaron Karas, Yash Patel, and Kristin Larsen

Have you ever wondered about the evolution of man’s best friend? Scientists believe it began between 30,000 and 130,000 years ago when humans began to control wolves. Today, as a result of mutation and artificial selection, there are hundreds of different breeds of dogs. Considering there are currently 339 breeds of dogs recognized by the World Canine Organization, it is easy to forget that they all belong to the same species. This profusion of breeds today reflects intense and purposeful interbreeding of dogs over the past 150 years.

The dog, Canis familiaris is a direct descendent of the gray wolf, Canis lupus. Genetic evidence from an ancient wolf bone discovered lying on the tundra in Siberia’s Taimyr Peninsula revealed that wolves and dogs may have split from their common ancestor at least 27,000 years ago. This first divergence was followed by what is thought to be the second divergence uncovered by research done in 2014. Ultimately this indicates that wolf populations from which dogs originated have gone extinct, and that the current wolf diversity from each region represents new, younger wolf lineages.

Since diverging from the gray wolf, the dog has undergone thousands of years of evolution. It may seem implausible that humans could have significantly altered the course of this species’ evolution considering this long time span. However, the idea that humans cannot influence evolution because it occurs over such long periods of time is a common misconception. Evolution does not necessarily occur over millennia. In fact, in some experiments it has been shown to occur in just a matter of weeks. In the case of dogs, a significant portion of the diversity that we see today can largely be attributed to the artificial selection that has occurred over the past 150 years. Artificial selection is the process by which humans intentionally breed a species with the hope of producing offspring with a particular set of traits. And this is what we see with dog breeding. Continued selection for certain traits within dog lineages eventually leads to the generation of new breeds, each of which has a unique form and personality.

For example, the German Shepherd breed first appeared in Germany in the late 19th century. The first declared German Shepherd was the result of decades of breeding dogs for the purpose of herding and guarding sheep. Desired traits, such as intelligence and strength, were thus being selected for. After continued selection for traits desired in a herding and guard dog, the German Shepherd evolved to become the notably territorial, loyal and attentive breed that it is today.

If you’re interested in learning more about this topic, please refer to the following articles:

Larson, G., E. K. Karlsson, A. Perri, M. T. Webster, S. Y. W. Ho, J. Peters, P. W. Stahl, P. J. Piper, F. Lingaas, M. Fredholm, K. E. Comstock, J. F. Modiano, C. Schelling, A. I. Agoulnik, P. A. Leegwater, K. Dobney, J.-D. Vigne, C. Vila, L. Andersson, and K. Lindblad-Toh. “Rethinking Dog Domestication by Integrating Genetics, Archeology, and Biogeography.” Proceedings of the National Academy of Sciences 109.23 (2012): 8878-883.

Shannon, Laura M., Ryan H. Boyko, Marta Castelhano, Elizabeth Corey, Jessica J. Hayward, Corin Mclean, Michelle E. White, Mounir Abi Said, Baddley A. Anita, Nono Ikombe Bondjengo, Jorge Calero, Ana Galov, Marius Hedimbi, Bulu Imam, Rajashree Khalap, Douglas Lally, Andrew Masta, Kyle C. Oliveira, Lucía Pérez, Julia Randall, Nguyen Minh Tam, Francisco J. Trujillo-Cornejo, Carlos Valeriano, Nathan B. Sutter, Rory J. Todhunter, Carlos D. Bustamante, and Adam R. Boyko. “Genetic Structure in Village Dogs Reveals a Central Asian Domestication Origin.” Proceedings of the National Academy of Sciences Proc Natl Acad Sci USA (2015): 201516215.

Parker, H. G. “Genetic Structure of the Purebred Domestic Dog.” Science 304.5674 (2004): 1160-164.

Skoglund, P., A. Gotherstrom, and M. Jakobsson. “Estimation of Population Divergence Times from Non-Overlapping Genomic Sequences: Examples from Dogs and Wolves.” Molecular Biology and Evolution 28.4 (2010): 1505-517.

Vila, C. “Multiple and Ancient Origins of the Domestic Dog.” Science 276.5319 (1997): 1687-689.

Akey, J. M., A. L. Ruhe, D. T. Akey, A. K. Wong, C. F. Connelly, J. Madeoy, T. J. Nicholas, and M. W. Neff. “Tracking Footprints of Artificial Selection in the Dog Genome.” Proceedings of the National Academy of Sciences 107.3 (2010): 1160-165.

Dogs and Wolves: What’s the Difference?

Contributed by Nadia Irfan and Joseph Birchansky

This is a graphic representation of the phylogenetic tree showing relatedness between dogs and wolves as it compares to outgroup (less related) species which branches off to form new species earlier on in history. The images show structural similarity and differences between the three species as well.

This is a graphic representation of the phylogenetic tree showing relatedness between dogs and wolves as it compares to outgroup (less related) species which branches off to form new species earlier on in history. The images show structural similarity and differences between the three species as well.

Dogs are the classic American pet, but how much do you really know about them? Dogs’ behavior is quite similar to humans’. For instance, even puppies that haven’t interacted with humans show social and cognitive skills on par with human children. This is surprising, considering their closest relative in the wild is the wolf, which is known to be more aggressive and less compatible with people. Wolves raised by humans don’t develop the same mental and social skills that domesticated dogs do. In addition, dogs are less fearful and more playful than wolves. This divergence is due to artificial selection by humans over many generations, which has resulted in dogs with improved tameness and temperament, which were reinforced by a population bottleneck – a significant reduction in population size.

Ancestors with dog-like characteristics originate in the fossil record up to 33,000 years ago. It appears dogs were first domesticated about 16,000 years ago, which actually happened before the development of agriculture. They then completely diverged from wolves 14,000 years ago, and there is evidence suggesting that dogs emerged from a single species of ancestral wolf. This divergence occurred via bottlenecks, significant reductions in population size, in both species, which were especially pronounced in dogs, from 32,000 to less than 2,000 individuals – a 16-fold reduction – and less so in wolves, which only experienced a threefold reduction. It is unclear why this reduction in wolves occurred, but it happened before humans began intentionally hunting them.

It’s interesting that, with so many behavioral and physical differences, dogs and wolves actually have very similar genomes. What’s different is which genes are being expressed, including those involved with cognition, memory, growth, and social skills. These differences in gene expression are driven in large part by artificial selection. Humans also influenced the morphology of dogs, including coat color variation, reduced cranial volume, and smaller skeletal size. These changes in morphology could potentially be deleterious because a possible effect of artificial selection may be a reduction in purifying selection, which ordinarily eliminates characteristics that are unfavorable in the wild. Research shows that humans may also have selected for behavioral traits, and these traits may have been selected for even before morphological traits. Not only did humans select for behavioral traits but food, shelter, and water availability given to them by humans are specifically responsible for differences in hypothalamic gene expression – a region associated with behavior and intelligence.

As a result of these selective pressures dogs have evolved different pack mentalities than wolves. Whereas wolves have a pair-bonded family unit that collaborates in hunting and rearing babies, dogs are less inclined to stay with one mate, are less active in raising their young, and are more dependent on human-provided resources. Overall, dogs’ and wolves’ different social, behavioral, and physical characteristics reflect speciation and domestication.

Also see: Who Helped the Dogs Evolve?

For more information, please refer to the following sources:

Albert, F.W., et al. 2012. A Comparison of Brain Gene Expression Levels in
Domesticated and Wild Animals. PLOS Genetics 8:9.

Freedman, A.H., et al. 2014. Genome Sequencing Highlights the Dynamic Early
History of Dogs. PLOS Genetics 10:1.

Li, Y., et al. 2013. Artificial Selection on Brain-Expressed Genes during the
Domestication of Dog. Molecular Biology and Evolution 30:8. 1867-1876.

Marshall-Pescini, S., Viranyi, Z, & F. Range. 2015. The Effect of Domestication on
Inhibitory Control: Wolves and Dogs Compared. PLOS ONE 10:2.

Ramirez, O., et al. 2014. Analysis of structural diversity in wolf-like canids reveals
post-domestication variants. BMC Genomics 15:.

Saetre, P., et al. 2004. From wild wolf to domestic dog: gene expression changes in
the brain. Molecular Brain Research 126:2 198-206.

Zhang, H. & Chen, L. 2011. The complete mitochondrial genome of dhole Cuon alpinus:
phylogenetic analysis and dating evolutionary divergence within canidae. Molecular
Biology Reports 38. 1656