This "bully" whippet has a mutation in its gene for the muscle growth-limiting factor myostatin that caused the canine to develop its striking overstuffed muscles. Dogs with one copy of the two–base pair mutation are faster and more athletic than normal whippets, but animals such as this one with two copies have severely overdeveloped muscles and often die prematurely. Researchers reported discovering the mutation in May's PLoS Genetics and suggested that the result could be the first of many genetic insights into enhanced athleticism in both humans and other animals.