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Using homologies to reconstruct relationships
After scientists have studied many traits in different species and figured out
which are probably homologous, the traits can be used to build an evolutionary
tree. Only homologous traits are evidence of shared ancestry. Homologous (but
not analogous) traits can be used to reconstruct the evolutionary relationships
between different species. For example, humans, chimpanzees, and gorillas all
have thumbs that are very similar anatomically and are homologous. The panda's
thumb, however, is analogous to these primate thumbs. This (along with lots of
other evidence) suggests that humans, chimpanzees, and gorillas are more closely
related to one another than any of them are to pandas.
Scientists don't always start with anatomy in determining if two structures are
homologous. Sometimes a phylogeny is used to help determine if a trait is homologous
or analogous; however, this phylogeny is based on other traits, not the trait in
question. This ensures that scientists' reasoning is not circular. Many different
pieces of evidence feed into such arguments, and scientists go with the conclusion
most consistent with the evidence. |
