Leonardo's love of animals has been documented both in contemporary accounts as recorded in early biographies, and in his notebooks. Remarkably for the period, he even questioned the morality of eating animals when it was not necessary for health. Statements from his notebook and a comment by a contemporary have led to the widely held view that he was vegetarian. Additionally, he categorized humans as being in the same set of species as apes and monkeys, just as he did with other animals in their respective genus. He also dissected dead animals for the purpose of comparative anatomy.