1+Structures+of+Evolution

A. Homologous structures are variations of the same structure that has enabled the organism to adapt to different environment. For example, the arm bone in animals (humans, birds, dolphins) has the same basic makeup, yet it's very different in its appearance and function.

B. Analogous structures have the same function, but suggest neither similarity in anatomy nor close relationship. Examples are wings used for flying by birds, bats, and insects. They all have wings that enable them to fly, but they are structured differently and not closely related.

C. Vestigial structures currently have no official function but may have been of use in the evolutionary past. Examples of vestigial structures include the human appendix, extra toe on dogs(called a dewclaw), and human coccyx.

D. These structures are important to the concept of evolution because they can suggest the origins of structures and how close some species are related. From our knowledge of homologous structures, we can assume that many animals (humans, birds, dolphins, etc.) with similar arm bones share a common ancestor that had the single upper bone (humerus), 2 lower bones (ulna and radius) and multiple phalanges. Analogous structures are the result of convergent evolution (the development of the same biological trait in unrelated lineages) and should be contrasted with homologous structures. Vestigial structures can tell us about the past of a species. The appendix in humans suggests that our ancestors ate more vegetation, but we have since changed our habitat and diet so our appendix no longer has any real function. We also often call our coccyx our tailbone, yet we have no tail. This surfaces the idea that our ancestors may have had tails, but our need for them apparently disappeared so the structure of a tail has disppeared as well.