Understanding Evolution: Natural Selection and Genetic Drift

1. April 25 Computer Lab Use the powerpoint to take your notes! Play the games and fill in your paper!

2. Why is it called Natural selection? • Darwin saw how similar it was to artificial selection • Artificial Selection – humans “select” which individuals to reproduce (selective breeding) ex: different breeds of dogs

3. Natural selection – Most fit individuals reproduce the most successfully • Selection – results in a change in the inherited characteristics of a population

4. Natural Selection….. Original Population (bugs) Predator Those that survived reproduced, making them more fit There is a change in allele frequency over time = evolution Over time, what do you think might happen?

5. Descent with Modification • Darwin proposed that over long periods, natural selection produces organisms that look very different from their ancestors. • He believed that each living species descended, with changes, from other species.

6. Descent with modification implies common descent  • Common Descent – all species (living and extinct) share a common ancestor and are distantly related to one another.

7. Evolution by Genetic Drift • In genetic terms, evolution is any change in the frequency of alleles in a population

8. Genetic drift – in small populations, individuals that carry a particular allele may produce more offspring randomly • (ex: natural disaster wipes out half of a population; survivors reproduce more)

9. #2. Random Genetic Drift • Genetic drift has the same result as natural selection (changes in characteristics and allele frequency) Original Population (bugs) AVALANCHE DESTROYS ½ the population randomly Those that survived reproduced, making them more fit There is a change in allele frequency over time = evolution Over time, what do you think might happen?

10. Evidence of Evolution 1. Paleontology • The study of fossils • Relative Dating: older rocks are further down • Absolute Dating: Uses radioactive isotopes and half-lives to tell age of rocks/fossils • Fossils allow us to “see” the changes in life over the different periods of time 

11. 2. Geographic Distribution of Species • Explains how similar organisms can be found over such long distances • Supports common ancestor (because when organisms share traits, they usually share a common ancestor) • Ex. Marsupials (kangaroos and opossums family)

12. 3. Embryology • Study of the development of organisms • At the early stages of vertebrate development, all the embryos look alike. • Shows deep rooted relationships in organisms

13. 4. Molecular Biology • Studies proteins (sequences of amino acids) in different organisms • The closer the amino acid sequences, the more likely it is the two species are closely related

14. 5. Comparative Anatomy • Homologous Structures • Similar characteristics b/c of relatedness (i.e. common ancestor) • Same form but different function • Ex: dog’s leg, human’s arm, bird’s wing, and whale’s fin

15. Analogous Structures • Shows how unrelated organisms, under similar selective pressures, over time evolved similar (analogous) structures SEPARATELY • Ex: a bat’s wing and an insect’s wing are both used to fly, but have totally different structures

16. Vestigial Organs • Organs that are “leftover” from a common ancestor that have no use but are still in the genes and are “seen” • Ex. • Wings of flightless birds • Hind leg bones in whales • Human Tailbone • Appendix • Gill slits in Embryos