A clade (from Ancient Greek: κλάδος, klados, "branch") or monophylum (see monophyletic) is a group consisting of an ancestor and all its descendants, a single "branch" on the "tree of life".[1] The ancestor may be an individual, a population or even a species (extinct or extant). Many familiar groups, rodents and insects for example, are clades; others, like lizards and monkeys, are not (lizards excludes snakes, monkeys excludes apes and humans).