Evidence for Descent with Modification

1. Direct Observation Guppy coloration HIV resistance

2. Fossil Record Species were different in the past Extinctions Transitional forms

3. Homology Variations on a structure that was present in a common ancestor – Ex: forearm bones of mammals, wings of birds and bats

Anatomical Homologies Vertebrate embryos – All have a tail and “throat pouches” during development CatHumanDolphin

Vestigial Structures Remnants of features that served important functions in ancestors – Ex: whale pelvic bones

Evolutionary Tree Use homologies to create a “tree” that show relatedness

Analogy Analogous traits are similar but not due to a common ancestor – Ex: wings of birds and insects

Convergent evolution Happens because of similar environmental pressures Organisms do not have a recent common ancestor but resemble one another – Ex: whales and sharks

4. Biogeography Use our understanding of Pangaea and continental drift to search for fossils

What Darwin didn’t know…. Now, we compare DNA and proteins to get a better idea of relatedness – More differences = more time since a common ancestor