Domesticated animals, compared to their wild counterparts, have undergone numerous changes in physiology, behavior and morphology. These changes are commonly referred to as the domestication syndrome and include behavioral changes, such as increased docility as well as genetic alterations in size, color and facial characteristics. In attempting to find whether these changes have a single cause, Russian zoologist Dmitry Belyaev conducted a series of selection experiments with silver foxes, hypothesizing that behavior, specifically tameness, was the key driving factor behind the changes brought about by domestication. After generations of selecting foxes for tameness, they were found to display phenotypes similar to those observed in domesticated species. Since then, it has been further hypothesized that selection for social tolerance and reduced aggression may also have played an important role in shaping the modern human anatomy, which is remarkable for the reduced face and gracile overall features.