The term homologous comes from the study of homology, the study of similarities between structures or body parts. We find within many the branches of biological science, homologous structures. Structures, which are similar in function in the different biological species and have evolved from the same structure and therefore are called homologous structures.
Comparative anatomy is the study of internal and external structures within and among species. In comparative anatomy the similarities and differences are compared within and among species, also. Comparative anatomy is very similar to evolutionary biology and phylogenics, which is the evolution of species. Within the study of comparative anatomy, we find two main concepts:Homologous structures and Analogous structures.
Homologous structures are those structures or parts within humans and other species, which are similar. The homologous body parts, often have similar functions. The developmental process or the origin of the structure lies in a similar environment. Homologous body parts may or they may not exist to perform the same function. Analogous structures or body parts similar in different species. These parts usually exist for the same or a similar purpose or function.
Some of the homologous and analogous structures of the human body: arms, legs, head, hands, eyes, procreative structures, hands, hearts, genes, blood and so on are some of the internal and external body parts of humans and other species.