The Downsides Of Canine Domestication
People domesticated wild dogs into what is today our loyal, friendly, and lovable canine companion about 25 thousand years ago. And although most folks agree that it was one of the best decisions mankind’s ever made, new evidence suggests that the domestication of wolves into dogs and the diversification of dogs into breeds may have increased the number of harmful mutations that dogs have in their genomes.
Certain breeds of dogs were created by not only selecting traits that humans found desirable but also saddling those breeds with deleterious mutations. There’s a number of evolutionary pressures that could theoretically lead to a build-up of disadvantageous mutations. One such force is a reduction in population size or ‘population bottleneck,’ which can disrupt natural selection’s ability to remove harmful mutations.
Another very important factor is positive selection, which is most obvious when you take a look at breeders who choose to propagate only certain traits such as docility or coat color. It’s not that big of an issue to do this (we wouldn’t have many of the fantastic breeds today otherwise), but the side effects are many, including the possibility to pass on deleterious mutations which are linked to the gene variants relevant for positive selection.
Kirk Lohmueller of the University of California, Los Angeles, and his team were in charge of conducting a study that gave us more insight on the topic of the flaws of domestication. They analyzed data from the genomes of 19 gray wolves, 25 semi-feral “village dogs” from 10 countries, as well as 46 breed dogs, three dogs per breed. Then they examined the genetic variation within each group and looked for evidence of deleterious alleles. They found out that dogs had about 115 more than wolves, which amounts to about 2.6 percent more deleterious variants.
This small increase in dogs’ genetic load is quite probably not enough to get all dog-lovers running around, screaming in panic. However, it does imply that the strong selection factors for all breed-specific traits favor what’s fashionable rather than necessarily functional or even healthy.