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Biologically, an animal is any member of the Animalia kingdom. Animals must eat [[plant]]s or other organisms to survive. The plants are called "producers" and the animals are "consumers". Scientists call consumers [[heterotroph]]s. Animals have complex [[eukaryotic cell]]s, unlike bacteria which have much simpler [[prokaryote|prokaryotic]] cells.  Animal cells do not have [[cell wall]]s, only structural [[protein]]s in the [[cell membrane]]; this allows the animal cell a certain amount of flexiblity.

An animal is any creature which is a member of the Animalia kingdom. Animals must eat [[plant]]s or other organisms to survive. The plants are called "producers" and the animals are "consumers". Scientists call consumers [[heterotroph]]s. Animals have complex [[eukaryotic cell]]s, unlike bacteria which have much simpler [[prokaryote|prokaryotic]] cells.  Animal cells do not have [[cell wall]]s, only structural [[protein]]s in the [[cell membrane]]; this allows the animal cell a certain amount of flexiblity.

Animals [[evolution|evolved]] from single-celled, colonial protists called [[choanoflagellate]]s.  The simplest of all animals are [[sponge]]s, which do not move, and are instead sessile.  Sponges have different cells for different tasks, but these cells are not organised further into tissues or organs.  Sponges also do not exhibit symmetry, a characteristic found in all other animals.

Animals are thought to have [[evolution|evolved]] from strange single-celled, creatures called [[protist]]s, which are neither plants nor animals.  The simplest of all animals are [[sponge]]s, which do not move.  Sponges have different cells for different tasks, but these cells are not organized further into [[tissue]]s or [[organ]]s.  Sponges also do not exhibit [[symmetry]], unlike all other animals.

The next simplest animals comprise a single species, placed between sponges and all other animals.  This species, ''Trichoplax adhaerans'', is very small, yet has differentiated cells organised into tissues, though not organs.  This shows an improvement upon the sponge body plan.

The next simplest animals comprise a single species, which fall somewhere between sponges and all other animals.  This species, ''Trichoplax adhaerans'', is very small, yet has cells organised into different kinds of tissues, though it does not have organs.  This is an improvement on the sponge body plan.

All other animals are grouped into a subkingdom called Eumetazoa (true animals).  All eumetazoans have tissues and organs, except for one phylum, Myxozoa, which have regressed to a single-celled form.

True Animals are grouped into a sub-kingdom called Eumetazoa.  All True Animals have tissues and organs, except for one type called Myxozoa. These have regressed to a single-celled form.

In the [[Bible]], [[God]] gave dominion over the animals to [[Adam]] and [[Eve]]. (Genesis 1:28)

In the [[Bible]], [[God]] gave dominion over the animals to [[Adam]] and [[Eve]]. (Genesis 1:28)