Unlike the predictions of the creationist model, there is no evidence to support the claim that animals have always existed. Most of the history of life on earth passed without a single animal. When animals first appear in the fossil record, there is not a single fish, mollusk, arthropod, reptile, mammal, or bird. If animals have existed since the beginning of life on earth or if modern animals have existed since the beginning of the fossil record of animals, then creationists should be able to find their remains.

Animals form a clade whose members are more closely related to each other than they are to any other type of eukaryote. Their shared similarities include the use of collagen in the extracellular matrix, greater intercellular interaction through amplification of existing eukaryotic gene families of cell membrane proteins, and greater control over cell division. Many genetic sequence comparisons have supported this animal clade in that animal sequences are more similar to each other than they are to a sequence from any non-animal.

Early animals evolved elements of the muscular system (such as ACh-E and contractile cells), reproductive system (such as an acrosome on sperm and large ova), and immune system (such as phagocytic amoeba-like cells, inflammatory cytokines, the ability to distinguish between self and nonself, and homologs of the lectins and complement that mammals use in complex immune cascades) which are shared among the diverse lineages of animals today. Sponges (the simplest animals alive today) possess some, but not all, of the components of the more complex systems of metazoan animals which undermines the “irreducible complexity” argument of intelligent design.