| MadSci Network: Genetics |
Hi Savannah,
There are many ways to define a species but, according to the biological species concept, two individuals belong to the same species if they have the capacity to breed and produce fertile offspring. There are a number of problems with this idea but it's still a very useful concept since it removes the connection between the way an animal looks (its morphology) and how it's classified (its taxonomy). For this reason it's possible to have very similar looking individuals which belong to different species (these are called sibling species) and very different looking individuals which belong to the same species (these are called polymorphic species). Domestic dogs are a textbook case of a highly polymorphic species. Every breed of dog from the smallest Chihuahua to the biggest Great Dane belongs to a single species; Canis familiaris.
There are several reasons why a species could be highly polymorphic but in the case of the domestic dog it is, as you suggest, likely to be due to selection by breeders for different characteristics which they have found useful or attractive. Since different breeds of dog were bred for different purposes the differences between them have become exaggerated over time. For more about the genetics and evolution of dogs check out the following websites...
From the mad scientist archives...
Other sites...
How dog breeds began
Domestication and
evolution
The
Dog Genome Project
The Canine Diversity Project
Regards,
Rob Cruickshank
Try the links in the MadSci Library for more information on Genetics.