An interesting science story from this week was about a study of dog genetics. Apparently, a single gene codes for a major growth factor in dogs, and all small dogs have a section of DNA that turns it off. In other words, one gene determines whether dogs are big or small.
I've often wondered at the astonishing variation in size among dogs. It seems amazing that animals as different as a chihuaha and a Siberian husky could be the same species. Domestic cats, by contrast, are nearly all close to the same size.
Since all modern dogs are descended from the grey wolf, small dogs are obviously the anomaly, the descendents -according to the authors of the study - of a miniature grey wolf that was born about 15,000 years ago. The absence of any tiny wolves running around today suggests that the gene regulator disappeared from the wolf genome a long time ago, undoubtedly because being a mini-wolf conferred no survival advantages on its possessors.
So why did the mini-dog gene survive and prosper? It seems likely that the anwser has something to do with humans. Maybe humans thought a miniature wolf was "cute" and sought to domesticate it, or protect and keep it. If so, their efforts could well have resulted in the mini-wolf producing healthy offspring, which themselves would have been cherished and looked-after by their human protectors.
The special relationship between dogs and humans has often been cited as one of the reasons for the remarkable success of dogs as a species. That relationship, it now appears, may go back much further than we had thought.