Evidence for Evolution

Scientists use a variety of techniques to determine evolutionary relationships

1. Fossil Record Reveals changes in populations over time Shows how structures have changed over time Has gaps = missing links

Horse Evolution

Dating Fossils Relative Dating - The Law of Superposition Younger rock layers are closer to the surface Older layers are buried deeper Age of fossils are RELATIVE depending upon position in rock layer

Radioactive Dating Unstable combination of protons and neutrons. Absolute Dating Use radioactive isotopes to determine the age of rocks and fossils Unstable combination of protons and neutrons. Eventually change into a more stable atom of another element

Radioactive Dating - cont’d All living organisms absorb C-12 and C-14 from the environment Once dead, it no longer absorbs the carbon C-14 begins to decay at a constant rate

Half-life: # of years it takes 50% of the original sample to decay

Radioactive Dating - cont’d C-14  N-14…½ life is 5730 years – only good for fossils less than 50, 000 years old K-40  forms inert gas Ar-40… ½ life is 1.26 billion years I have 12 g of C-14. How much C-14 will I still have in 17,190 years? A piece of fossilized wood has a C-14 radioactivity that is 1/4 that of a new piece of wood. How old is the fossilized wood?

2. Comparative Anatomy Homologous structures = Similar function Found on different species Thought to be inherited by a COMMON ANCESTOR Human arm, whale fin, bat wing

Comparative Anatomy – cont’d Analogous structures Similar in function NOT inherited from a common ancestor Butterfly wing, bird wing

Comparative Anatomy – cont’d Vestigial structures Inherited Homologous structure REDUCED IN SIZE & OFTEN UNUSED Python hip bones, human tail bone

Vestigial Structures in Humans?

3. Embryology The study of the early stages of an organism’s development ALL vertebrate embryos have gill pouches  thought to be inherited from a COMMON ANCESTOR

4. Biochemistry The study and comparison of chemicals found in living things *DNA base pairs & proteins* Mostly use hemoglobin & mitochondrial DNA More similarities = more closely related