1. Evidence for Evolution

2. Scientists use a variety of techniques to determine evolutionary relationships

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

4. Horse Evolution

5. 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

9. 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

10. 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

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

12. 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?

13. 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

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

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

16. Vestigial Structures in Humans?

17. 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

18. 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