Across
- 1. theory that evolution occurs in small gradual steps over time
- 5. anatomically similar structure inherited from a common ancestor
- 6. shift of a population toward an extreme version of a beneficial trait
- 8. amount of time required for half of a radioactive isotope to decay
- 9. Darwin's term for the selective breeding of organisms selected for certain traits in order to produce offspring having those traits
- 12. process in which individuals with average traits are removed; creates two populations with extreme traits
- 15. most common form of natural selection in thich organisms with extreme expressions of a trait are removed
- 18. structure that has the same function but different construction; not inherited by a common ancestor
- 19. process in which a large population declines in number then rebounds
- 20. preserved evidence of an organism found in sedimentary rock
- 21. diversification of a species into a number of different species
Down
- 2. method used to determine the age of rocks by comparing
- 3. explains that eukaryotic cells may have evolved from prokaryotic cells
- 4. theory that evolution occurs with relatively sudden periods of speciation followed by long periods of stability
- 7. change in the frequency of a trait based on competition for a mate
- 10. states that the oldest layers of rock are found at the bottom and the youngest layers are found at the top
- 11. hereditary changes in groups of living organisms over time
- 13. reduced form of a funtional structure that indicates shared ancestry
- 14. theory of evolution developed by Darwin based on four ideas
- 16. random change allelic frequencies in a population
- 17. random effect that can occur when a small population settles in an area separated from the rest of the population and interbreeds