Sociobiology is the study of animal behaviour from an evolutionary perspective. It played a major role in Darwin's Origin of Species, but then lay undeveloped until the 1960s. It proved very controversial, especially when applied to humankind, with social scientists and left-wing biologists arguing that it was racist, sexist, unfalsifiable and untrue. Some of these criticisms were well taken but in recent years sociobiology, including the human application, is much more solid and defensible.