Descent with Modification

Natural Selection: 1. Resources are limited. (There’s not enough for everybody.) 2. We have more offspring than we can support. 3. Not everybody will survive – those best suited to their environment are most likely to survive. 4. Only survivors pass their genes to the next generation.

Supporting Evidence: 1. Direct Observation -- evolution of drug resistance ------ resistant HIV ------ MRSA ------ resistant TB

2. Fossil Record Some organisms have become extinct New groups of organisms appear Groups of organisms change gradually over long periods of time

3. Homology Similar characteristics due to common ancestry Homologous structures: anatomical structures with similar basic makeup, but differences due to adaptations to different environments

Vestigial structures: leftover structures that served important functions in an organism’s ancestors

Embryology: vertebrate embryos are very similar to each other in early stages of development, relating back to a common ancestor

Amino acid and DNA sequences: the more closely related two species are, the greater the similarity in their DNA makeup

4. Biogeography: geographic distribution of species -- due to continental drift -- can explain locations of fossils