Tinbergen's four questions, named after Nikolaas Tinbergen, are complementary categories of explanations for animal behaviour. These are also commonly referred to as levels of analysis. It suggests that an integrative understanding of behaviour must include: ultimate (evolutionary) explanations, in particular the behaviour (1) adaptive function and (2) phylogenetic history; and the proximate explanations, in particular the (3) underlying physiological mechanisms and (4) ontogenetic/developmental history.