Wednesday, March 17, 2010
On pages 125 to 126, Jerry Coyne discusses the large variety of breeds found in dogs today. Having stated that the dog species as a whole "comes in all shapes, sizes, colors, and temperaments," it makes sense that these numerous breeds would be considered separate species if found in fossil form at a later date, as the wide variation of traits would lend itself to that conclusion. However, it is quite clear that "dog" is still a singular species today, as shown when one breeds a purebred toy poodle with a purebred pug. Both very different in terms of traits, yet they still can make "puggles" no problem at all. Yet, it wouldn't be such a good idea to breed a toy poodle with, say, a great dane as the fetus of a great dane - poodle cross would certainly not be able to develop in such a small dog. They are still breeds of the same species, so how could they not reproduce? How could this be? The implication behind this is that not all breeds of dogs can mate with one another successfully, so some separation exists within the species. When does that line between "breed" and "species" get crossed? It would be wise to take your response beyond a simple "when they can't reproduce with each other anymore" as the line is obviously blurred in the case of dog breeds.