This sequence is also supported by many other types of evidence. Comparative anatomy Anatomical similarities among species grouped in the same taxonomic category are a reflection of their common descent. Although the limbs are used for different functions, it is obvious that the same skeletal elements are present. It is logical that whether the forelimb is a foreleg, wing, flipper, or arm, the basic similarity is the consequence of descent from a common ancestor and that the limbs have been modified for different functions. Other evidence from comparative anatomy supports that evolution is a remodeling process in which ancestral structures that functioned in one capacity have become modified as they take on new functions.
Some homologous structures are vestigial organs.
Vestigial organs are remnants of structures that had important functions in ancestral forms but are no longer essential. The remnants of pelvic and leg bones in snakes show descent from a walking ancestor, but have no function in the snake. Because it would be wasteful to continue providing blood, nutrients, and space to structures that no longer have a major function, vestigial organs serve evidence of evolution by natural selection. Comparative embryology Closely related organisms go through similar stages in their embryonic development. As development progresses, the gill slits develop into divergent structures characteristic of each vertebrate class.