It may have been a butterfly that first started me thinking seriously about biology. It was early spring; I was perhaps twelve or thirteen years old and sitting in the garden when a quivering yellow butterfly flew over the fence. It turned, hovered and briefly settled—just long enough for me to notice the elaborate veins and spots on its wings. Then a shadow disturbed it and it took flight again, disappearing over the opposite fence. That intricate, perfectly formed butterfly made me think. It was both utterly different to me and yet somehow familiar too. Like me, it was so obviously alive: it could move, it could sense, it could respond, it seemed so full of purpose. I found myself wondering: what does it really mean to be alive? In short, what is life?