Bilateral Symmetry

This is a picture of a bird. It has bilateral symmetry. An organism with bilateral symmetry can be divided into mirror halves through a single plane. Organisms with bilateral symmetry do not necessarly have to have both halves as perfect mirror images – often one foot or ear can be bigger than another and internal organs are not symmetric in their shape or positioning. Most organisms have bilateral symmetry including worms, insects, fish, birds, and mammals, including humans. In evolution, bilateral symmetry was important for the development of a head and the concentration of sensory organs.