1. Development of Darwin’s idea

3. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation has a genetic component (can be inherited). 3. Differential reproductive success among members of the population. Survival and reproduction is, on-average, nonrandom 4. Phenotypic variation shifts between generations in response to a changing environment.

4. Adaptive radiation Galapagos finches

5. Medium ground finch Geospiza fortis generation time: 4.5 years life span c. 16 years

6. 120 m N = c. 1,200 Research of Peter and Rosemary Grant: 1973 - present Hot spot 7 cm/yr 4-5 my 2-3 my 1 my

7. 1: Is the population phenotypically variable? Geospiza fortis

8. 2: Is the variation heritable? (heritability: proportion of phenotypic variation due to genetic variation; c. 65%) Evolution!

9. 1977: drought 130 mm precipitation dropped to 24 mm The base level natural selector Was there differential survival? Effect of natural selection

10. 1. 2. 3. The interplay Seed abundance Number of finches The second level natural selector Seed characteristics of surviving plants

11. Had evolution taken place? Significant difference in beak size. Note: natural selection is always one generation behind the expression of modified phenotypes

12. Natural selection cannot anticipate future “needs” of a population Evolutionary change is based selection in the previous generation. 1. Parental population + environment (natural selectors) 2. Part of population selected to reproduce 3. Transmission of heritable characteristics to the new generation (e.g., size of the beak). – But the change was based on phenotypic variation among their parents.

13. : species originate by divergence from common ancestors Evolution tends to take a branching form.

14. Darwin’s 1859 illustration ( On the Origin of Species by Means of Natural Selection )