Although structures usually called 'vestigial' are largely or entirely functionless, a vestigial structure may retain lesser functions or develop minor new ones. These are typically in a degenerate, atrophied, or rudimentary condition, and tend to be much more variable than similar parts. Vestigial structures are often called vestigial organs, although many of them are not actually organs. Some genes no longer code for anything, and can thus be said vestigial themselves, or junk DNA. All such characters can in turn can be traced to the genes which code for such characters. Some of these disappear early in embryonic development, but others are retained in adulthood.

These may take various forms such as anatomical structures, behaviors and biochemical pathways. Vestigiality describes homologous characters of organisms which have lost all or most of their original function in a species through evolution. The human vermiform appendix is a vestigial structure it no longer retains its original function.

Vestigial structures download free