The Dog-Human Relationship
In addition to tameness, another unique trait of dogs is their ability to understand humans. For example, if you point or even shift your gaze toward a certain object (say, a jar that contains dog treats), a dog will likely investigate the object (Hare & Tomasello, 2005). Even our closest animal relatives, chimpanzees, do not have this skill. Brian Hare, a German researcher, posits that this is an example of convergent evolution—the emergence of a trait (referred to by Hare as “social skills”) that developed independently in two species. Hare’s working hypothesis is that domestication comes first, and after the fear response has been tuned down enough, the development of social skills can take place.
Domestication of dogs has occurred over many millennia. More recently, the advent of controlled breeding practices has segregated genetic variability into distinct phenotypes. In fact, the evolution of the majority of dog breeds is a relatively recent phenomenon, beginning with selective breeding practices during the past 200 years. Today, various breeds demonstrate a huge variability in size and shape, as well as coat characteristics. Behavioral traits have also been bred based on humans’ use of dogs for herding, hunting, guarding, and companionship. Phenotypic variation among dogs is currently partitioned into more than 350 distinct breeds worldwide; these breeds are largely closed populations that receive little genetic variation beyond that which existed in the original founders (Ostrander & Wayne, 2005).
“These restrictive breeding practices reduce effective population size and increase overall genetic drift among domestic dogs, resulting in the loss of genetic diversity within breeds and greater divergence among them,” writes Ostrander, who participated in a landmark study of the genomic relationship of 85 different dog breeds. “For example, variation among breeds accounts for 27% of total genetic variation, as opposed to 5-10% among human populations” (Parker et al., 2004). Now that the dog genome has been sequenced, the potential to learn more about man’s best friend, and perhaps ourselves, has increased (Ellegren, 2005).