Evidence for Evolution

1. Fossil Evidence 2. Biogeograpy 3. Anatomy 4.Comparative embryology 5.Molecular Biology

1. Fossil Evidence  Fossils appear in chronological order in layers of sedimentary rock  Fossils in young layers of rock are more similar to species alive today.  This is the strongest piece of evidence.

1. Transitional fossils Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms.

Here is a picture of the archeopteryx fossil This showed the transition from reptile to bird.

2. Biogeography: The past and present geographical distribution of species. The past and present geographical distribution of species. Geographically close environments are more likely to be populated by related species than geographically separate areas. Geographically close environments are more likely to be populated by related species than geographically separate areas. Animals on islands often closely resemble animals on the closest continent. Animals on islands often closely resemble animals on the closest continent. on/educators/teachstuds/svide os.html on/educators/teachstuds/svide os.html

3. Anatomy Homologous structures: Homologous structures: structures that are similar in form and origin (common ancestry) but have a different functions. Ex. Bat wings and human hands Ex. Bat wings and human hands Analogous structures: Analogous structures: Structures that perform a similar function but do not have a common evolutionary origin. Ex. Insect wings and bat wings

3. Anatomy (cont.) Vestigial structures: are reduced forms of structures that once were useful in ancestors. Ex. Pelvic bone in whales Vestigial structures: are reduced forms of structures that once were useful in ancestors. Ex. Pelvic bone in whales Top 10 Useless Limbs and Vistigial Organs organs.html organs.html

4. Comparative embryology: Study of structures that appear during embryonic development. Study of structures that appear during embryonic development. Similarities in development are indicative of common ancestry. Similarities in development are indicative of common ancestry. NOVA Video Common Past, Different Paths

4. Embryonic development For example, all vertebrate embryos have structures called pharyngeal pouches in their throat at some stage in their development. These embryonic structures develop into very different, but still homologous, adult structures, such as the gills of fish or the eustacian tubes in mammals.

5. Molecular Biology By comparing the DNA or RNA of different organisms, scientists can determine their degree of relatedness. Also, scientists can compare the amino acid sequences that make up proteins in different organisms.

Phylogenetic Trees The process of evolution produces a pattern of relationships between species. As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships. By studying inherited species' characteristics and other historical evidence, we can reconstruct evolutionary relationships and represent them on a "family tree," called a phylogenetic tree.

Evolution Video Origin of Life (David Attenborough, BBC, 1hour)