1. Evolution by Natural Selection
Struggle for Existence
Members of each species compete for food, space, and necessities of live.
Predators that can run faster catch more prey
Prey that are better camouflaged avoid being caught.

2. Evolution by Natural Selection
Survival of the Fittest
Survival depends on how well-suited an organism is to its environment
Fitness: ability to survive and reproduce
Adaptation: any inherited characteristic that increases an organism’s chance for survival.
Darwin called survival of the fittest natural selection
Underwater Astonishments

3. Evidence of Evolution Fossil Record
Diff. layers of rock form a different times in the Earth’s history.
Fossils show gradual change over time.

4. Evidence of Evolution Biogeography
Finches found all over the world evolved different adaptation to survive in their habitat.
Finches on the Galapagos evolved from a mainland species.
Darwin found that animals in similar habitats evolved similar characteristics.

5. Evidence of Evolution Homologous Body Structures
Structures that develop from the same embryonic tissue but have different mature forms.
Suggest evidence that organism descended with modification from a common ancestor.

6. Evidence Evolution Similarities in Early Development
Early embryo stages of many vertebrates look very similar.
The same groups of embryonic cells, develop in the same order, in similar patterns, to produce homologous structures.

7. Significance of biochemical differences

8. Vestigial structures – structures that have no function in the living organism but may have been used by its ancestors.
Ex: human appendix,
python leg bones

9. DNA evidence – the more similar the genes are, the more closely related organisms are thought to be.
Direct observation – We’ve seen evolution occur in cases like:
Bacteria becoming resistant to antibiotics
Insects that become resistant to pesticides

10. 17.3 The Process of Speciation
Species - group that can interbreed and produce fertile offspring.
Speciation – the formation of new species, occurs whenever reproductive isolation develops

11. Reproductive isolation develops by:
17.3 The Process of Speciation
Reproductive isolation develops by:
Behavioral Isolation
Geographic Isolation
Temporal Isolation

12. Behavioral Isolation Two populations are capable of interbreeding
Differences in mating rituals prevent interbreeding
Ex: Similar birds will not interbreed b/c of different mating songs

13. Geographic Isolation
2 populations are physically separated by barriers
Rivers
Mountains
Bodies of water

14. Temporal Isolation Two or more species reproduce at different times
Ex: One form of cicada emerges every 17 years, the other emerges every 13 years.

15. 17.3 The Process of Speciation
How do new species evolve?
1. Founders arrive – A few finches travel from South America to one of the islands. There, they survive and reproduce.
2. Geographic Isolation – Some birds from species A cross to a second island. The two populations no longer share a gene pool.

16. 17.3 The Process of Speciation
3. Changes in the Gene Pool – Seed sizes on the second island favor birds with larger beaks. The population on the second island evolves into a population, B, with larger beaks.
4. Behavioral isolation – If a few population-B birds cross back to the first island, they will not mate with the birds of population A. The gene pools are now separate. Populations A and B are separate species.

17. 17.3 The Process of Speciation
5. Ecological Competition – As species A and B compete for seeds on the first island, they continue to evolve. A new species, C, may evolve.
6. Continued Evolution – The process continues, leading to the formation of all 13 finch species on the Galapagos.

18. Chapter 17: Evolution of Populations

19. Populations and Gene Pools
17.1 Genes and Variation
Populations and Gene Pools
Population – a group of individuals of the same species that mate and produce offspring
Gene pool – all genes and the alleles for those genes present in a population
Allele frequency – the number of times an allele occurs in a gene pool compared to the total number of alleles in that pool for the same gene.

20. Populations and Gene Pools
17.1 Genes and Variation
Populations and Gene Pools
Take home message: Evolution, in genetic terms, involves a change in the frequency of alleles in a population over time.
Note: Although natural selection acts on individuals it is the population that evolves, not individuals

21. 17.2 Evolution as Genetic Change in Populations
Genetic Drift
Genetic Drift = random change in allele frequency
Acts on small populations
These chance occurrences can cause an allele to become more or less frequent in a population

22. 17.2 Evolution as Genetic Change in Populations
Genetic Bottlenecks
Genetic Bottleneck = a change in allele frequency following a dramatic reduction in the size of a population
Could result from disease, rapid climate or environmental change
Can reduce a populations genetic diversity

23. 17.2 Evolution as Genetic Change in Populations
Founder Effect
Founder Effect = when allele frequencies changes as a result of the migration of a small subgroup of a population
Creates a new gene pool that could be different from the parent population

24. Single-Gene and Polygenic Traits
17.1 Genes and Variation
Single-Gene and Polygenic Traits
Single-Gene Trait
Controlled by one gene that has two alleles
Two distinct phenotypes
Ex: bands or no bands on snails
Polygenic Trait
Controlled by more than one gene
Many possible genotypes and phenotypes
Ex: Human Height

25. Stabilizing selection

26. Directional selection

27. Disruptive selection