 A similar lesson can be learned even when moving further along the historic branches of a schematic tree of life to gain insight into the origin and diversification of metazoans. Although classic schemes do not include the origin of metazoans as a major transition, it is nevertheless a diversification of particular importance from a human perspective (Carroll 2001). Even if the origin of eukaryotes is thought to be uninteresting, because their original state is necessarily unicellular, nobody would disagree that the origin of metazoans is highly pertinent to understanding human evolution, since all metazoans are multicellular and humans are a group within them.