1. EVIDENCE OF EVOLUTION I
Chapter 15-2

2. Evolution defined
Change of heritable traits within a population over time
Evolution is a process of gradual modifications over generations
Darwin called this descent with modification

3. Common Ancestor All organisms share a common ancestor
Organisms today deviated from that common ancestor over time

4. Evidence for Evolution 1. Fossils
Fossils provide geologic evidence of evolution
Relative age: fossils are older in lower layers than those in the upper layers
Law of Superposition

5. Fossils - Transitional Species
Descent with modification states that newer species are modified versions of older species
Fossil record contains the intermediates

6. 3. Homologous Structures
Homologous Structures: body parts that are similar in structure may have different functions
Indicating at in the past they did the same job and came from a common ancestor

7. Analogous Structures
Analogous Structures: same functions but different development
Indicates that different populations evolved to be better suited to the same environment

8. 2. Vestigial structures
Vestigial structures- remnants of organs or structures that had a function in an early ancestor
Shows that these organisms are descendants from organisms that used them
Ex: (tailbone coccyx or hip bones in whales)

9. Evidence for Evolution -Biogeography
Geographical distribution of living things
Similar species are found in similar places showing common ancestry

11. Continental Drift
The continents have not always been in the position they are now
Fossils of the same ancient species have been found on different continents
Providing evidence that they were once connected