My research is focused on why some animals regenerate their limbs while others (mammals) do not. This is a question that has been asked for centuries, and there is probably no one answer. However, I have focused on a mammalian tumor suppressor that does not exist in highly regenerative species. This gene, ARF, is a very sensitive sensor of proliferative signaling, and we hypothesize that ARF evolved to strengthen tumor fighting mechanisms at the expense of regenerative abilities.