Basis for Classification

As we gather more evidence, classifications systems will change. Modern classification uses evolutionary evidence from 3 areas.

1. Anatomy Scientists compare body parts that may be homologous parts; some are vestigial structures. Homologous parts- similar because structures share a common ancestry ex- forelimb of vertebrates Vestigial structures- structure no longer functioning, left over from ancestor. Ex- tailbone, appendix

Analogous parts- parts that do not share a common ancestor, but similar because are used for similar function. Ex- wings of bird and wings of butterfly.

Use fossil evidence to relate current organisms to extinct organisms.

2. Embryology Scientists compare developing embryos.

3. Biochemistry Scientists compare genetic codes ex-amino acid or DNA sequences Also body chemistry ex- hormones, blood The more nucleotide sequences organisms have in common the more related they are.

Species Amino acid differences with human hemoglobin Gorilla 1 Rhesus monkey 8 Mouse 27 Chicken 45 Frog 67 Lamprey 125