An order of mammals that includes the monkeys, apes, and humans. Primates evolved from arboreal insectivores, known as proto-primates, probably some 55–65 million years ago. Living primates are characterized by thumbs and big toes that are opposable (i.e. capable of facing and touching the other digits), which permits manual dexterity, and forward-facing eyes allowing binocular vision. The brain, particularly the cerebrum, is relatively large and well-developed, accounting for the intelligence and quick reactions of these mammals. The young are usually produced singly and undergo a long period of growth and development to the adult form. See also hominin.

https://www2.palomar.edu/anthro/primate/ Wide-ranging account of primate characteristics and taxonomy, compiled by Dennis O’Neil, Palomar College, California