As far back as the 19th century it was apparent to some biologists that a simple, repeated pattern underlay the differing body structures of animals. It could be seen in the segmented bodies of ...

Among them were the chordates, to which vertebrates (animals with backbones ... at levels needed to fuel the growth of more complex body structures and ways of living. The environment also ...

All animal evolution for the last half billion ... providing fuel for movement and the evolution of more complex body structures. Others propose that an extinction of life just before the Cambrian ...