<Li> Homologous structures - structures (body parts / anatomy) which are similar in different species because the species have common descent and have evolved, usually divergently, from a shared ancestor . They may or may not perform the same function . An example is the forelimb structure shared by cats and whales . </Li> <Li> Analogous structures - structures similar in different organisms because, in convergent evolution, they evolved in a similar environment, rather than were inherited from a recent common ancestor . They usually serve the same or similar purposes . An example is the streamlined torpedo body shape of porpoises and sharks . So even though they evolved from different ancestors, porpoises and sharks developed analogous structures as a result of their evolution in the same aquatic environment . This is known as a homoplasy . </Li> <P> Comparative anatomy has long served as evidence for evolution, now joined in that role by comparative genomics; it indicates that organisms share a common ancestor . </P> <P> It also assists scientists in classifying organisms based on similar characteristics of their anatomical structures . A common example of comparative anatomy is the similar bone structures in forelimbs of cats, whales, bats, and humans . All of these appendages consist of the same basic parts; yet, they serve completely different functions . The skeletal parts which form a structure used for swimming, such as a fin, would not be ideal to form a wing, which is better - suited for flight . One explanation for the forelimbs' similar composition is descent with modification . Through random mutations and natural selection, each organism's anatomical structures gradually adapted to suit their respective habitats . The rules for development of special characteristics which differ significantly from general homology were listed by Karl Ernst von Baer as the laws now named after him . </P>

What is the purpose of comparing bone structures