Biogeography is the study of where organisms live now and where are they and their ancestors lived in the past. The first pattern of bio geography is a pattern in which closely related species differentiate in slightly different climates. The second pattern is a pattern in which very distantly related species develop similarities in similar environments.
Structures that are shared by related species and that have been inherited from a common ancestor are called homologous structures. Biologist test whether structures are homologous by studying the way structures develop in embryos and the pattern in which they appeared over evolutionary history.
Analogous structures our body parts that share common function, but not structure. An example is the wing of a bee and the wing of a bird. Vestigial structures are inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on the descendent. An example of a vestigial structure is the legs of the Italian three-toed skink.
Similar patterns of embryological development provides further evidence that organisms have descended from a common ancestor. Researchers noticed that the early developmental stages of vertebrates look very similar. Observations make it clear that the same groups of embryonic cells develop in the same order and in similar patterns to produce many homologous tissues and organs in vertebrates. Darwin realize that similar patterns of development gives important clues to the ancestry of living organisms.
At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent. An example of molecular evidence for evolution is that all living cells use information coded in DNA and RNA to carry information from one generation to the next. This genetic code is nearly identical in almost all organisms.