Dog's faces come in more shapes and sizes than the variation across the entire wolf, jackal and coyote family, report biologists, providing an example of extreme evolution.
In the current American Naturalist journal, researchers led by Abby Grace Drake of the United Kingdom's University of Manchester looked at 106 dog breeds as well as the skulls of other creatures in the canine family.
"The amount of shape variation among domestic dogs far exceeds that in wild species, and it is comparable to the disparity throughout the Carnivora (entire range of carnivore mammals)," says the study. Measuring 50 "landmarks" from the skulls of 677 dogs as well as 122 representatives of the carnivorous mammals, including cats, weasels, bears and seals, the team finds as much diversity in dog skull shapes, particularly for companion breeds, as exists within the entire 42-million-year-old carnivore family.
As far back as Darwin, naturalists have looked at how breeders have selected dogs for specific traits, the study notes, fast-forwarding evolution of new ones. "As a result, domestic dogs have a vast spectrum of cranial variation, which has clear functional consequences, for instance, on bite forces or breathing," says the study. "These novel skull shapes, as well as the disparity in dog breeds and in wild species, suggest that diversification of dog skull shapes is due, at least in part, to the radical change of the selective regime, as dog breeds were derived from wolves through domestication and the later establishment of modern breeds."
In the wild, natural selection doesn't allow the development of carnivores that have trouble breathing or chewing, such as pugs, the authors conclude. Investigating the genetic changes that allow such a wide proliferation of skull shapes to develop would inform both studies of evolution and bone growth, they suggest.