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

Cat Human Dolphin

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