Dogs Big And Small
To continue the dog theme, just by looking at the various phenotypes, it's pretty obvious there is a much greater physical variation present in dogs versus humans. According to this article, dogs actually show the greatest variation of all land animals (no doubt due to their selective breeding by man). So, if they're all the same species, why do they look so differently? Part of the answer, at least in terms of size, is illuminated by this recent study which found that a gene common to humans, insulin-like growth factor 1 (IGF-1) is responsible for regulating growth. Studying the genetic makeup of dogs not only satisfies our curiosity, but also provides help for understanding some of the diseases we share, like cancer, high blood pressure, arthritis, and many others. Check out the article in the paper, or go to your local library to read the study itself in the journal Science.