Humans are vertebrates—animals
with backbones—as are many of the animals we interact with and
observe in our daily environment. Our curiosity about this group of
animals is natural. The vertebrates include some of the largest and
fastest animals on Earth.
But the vast majority of animal
species, and individual animal organisms, are invertebrates. All
animals have an invertebrate ancestry.
As we proceed in our survey of
animals from invertebrates to vertebrates, well examine two of
the most widespread and successful groups of protostome
invertebrates, the mollusks and the arthropods.
Well then make our way
toward the vertebrate branch of the tree of life with an exploration
of the two most important phyla of deuterostomes, the echinoderms
and the chordates.
Well see how the vertebrate
line arose from the chordates and progressed through fish to land
animals, and well find the twig on the tree where the human
species is placed.