The Theory of Evolution

1. TheTheory of Evolution

2. Background: Darwin Darwin’s Ideas • Natural Selection • A process in which some individuals have genetically-based traits that improve survival or reproduction • Thus, they have more offspring surviving to reproductive age than other individuals.

3. Background: Darwin Darwin’s Ideas • Common Ancestry • All life forms share a common ancestor • We are all in the same “tree of life”

4. Background: Definition The Definition of Evolution • Descent with Modification • Small-scale evolution: Changes in gene frequency in a population from one generation to the next • Large-scale evolution: The descent of different species from a common ancestor over many generations. • What exactly is being modified?

5. Background: Definition Which of these represents descent with modification? Big Beetles go through a drought and have limited food Next generation is physically smaller due to lack of food 90% of the beetles have the gene for green color 30% of the beetles have the gene for green color

6. Mechanism: 1. Mutation How does this “descent with modification” happen? • Mutation • A change in a DNA sequence • usually occurring because of errors in replication or repair. • Mutation is the ultimate source of genetic variation.

7. Mechanism: 2. Migration How does this “descent with modification” happen? • Migration • Individuals from one group move into another group. • Making the gene more frequent in the population. gene flow

8. Mechanism: 3. Genetic Drift How does this “descent with modification” happen? 3. Genetic Drift In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals.

9. Mechanism: 3. Genetic Drift Genetic Drift: A game of chance • Imagine a game in which you have a bag holding 100 marbles • 50 of which are brown and 50 green. • You are allowed to draw 10 marbles out of the bag. • Now imagine that the bag is restocked with 100 marbles • with the same proportion of brown and green marbles as you have just drawn out. • The game might play out like this:

10. Mechanism: 3. Genetic Drift What effect does Genetic Drift have on Evolution? • Drift reduces genetic variation in populations, potentially reducing a population’s ability to evolve in response to new selective pressures. • Genetic drift acts faster and has more drastic results in smaller populations. This effect is particularly important in rare and endangered species. • Genetic drift can contribute to speciation. For example, a small isolated population may diverge from the larger population through genetic drift.

11. Mechanism: 3. Genetic Drift Examples of Genetic Drift • Population Bottleneck • An event in which a population’s size is greatly reduced Northern Elephant Seal Event that causes the population to be reduced in size Initial Diverse Population Final population Cheetah

12. Mechanism: 3. Genetic Drift Examples of Genetic Drift • Founder Effect • Changes in gene frequencies that usually accompany starting a new population from a small number of individuals.

13. Mechanism: 3. Genetic Drift Driftworm Activity • Put your IntNB to the side, and get out: • Your colored pencils and • The worksheet you picked up when you came in • Color in Generation 0 of your driftworms

14. Mechanism: 3. Genetic Drift Driftworm Activity • Each of these worms reproduces asexually • The population size is constant • The generations do not overlap • These are haploid organisms

15. Mechanism: 3. Genetic Drift Driftworm Activity • Roll the die and put a dot next to the corresponding worm. • Put a dot next to the corresponding number (the one you land on) • Do this five times (for each individual in the population)

16. Mechanism: 3. Genetic Drift Driftworm Activity • Repeat this until one allele is “fixed” in the population. • That is, until there is only one phenotype in the population.

17. Mechanism: 3. Genetic Drift What factors prevent an allele from becoming “fixed” in a population? • Mutation • Migration (Immigration and Emigration)  this is sometimes called “gene flow” • Mating (Sexual Reproduction) • A large population (to avoid the effects of genetic drift) • and…

18. Mechanism: 4. Natural Selection How does this “descent with modification” happen? • Natural Selection • A process in which some individuals have genetically-based traits that improve survival or reproduction • They have more offspring surviving to reproductive age than other individuals.

19. Mechanism: 4. Natural Selection Basic requirements of Natural Selection • There is variation in traits. • There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. • There is heredity.

20. Mechanism: 4. Natural Selection Types of Selection • Artificial Selection: • Farmers and breeders have been only allowing plants and animals with desirable traits to reproduce.

21. Mechanism: 4. Natural Selection Types of Selection • Stabilizing Selection: • Genetic Diversity decreases as a population stabilizes on a particular genetic trait. • Extreme traits are selected against.

22. Mechanism: 4. Natural Selection Types of Selection • Disruptive Selection: • Selection that favors the extremes of the distribution

23. Mechanism: 4. Natural Selection Types of Selection • Directional Selection: • One allele is favored over another, and the population shifts in one direction

24. Mechanism: 4. Natural Selection Which of type of selection is/can be caused by the following… • Human birth weight • Answer: Stabilizing Selection • The finches Darwin observed on the Galapagos Islands • Answer: Disruptive Selection • Lighter moths being selected by predators after the trees became covered with soot (post Industrial Revolution) • Answer: Directional Selection

25. Mechanism: 4. Natural Selection Directional Selection • Industrial Melanism Activity:

26. Mechanism: 4. Natural Selection Directional Selection • We will collect individual and class data and see if selection took place. • Draw the following data table in your IntNB.

27. Mechanism: 4. Natural Selection What is the general way we refer to those who survive? • Fitness: • a genotype’s success at reproducing • (the more offspring the genotype leaves, the higher its fitness). • Fitness describes how good a particular genotype is at leaving offspring in the next generation relative to other genotypes. Is this always the biggest, fastest and strongest?

28. Mechanism: 4. Natural Selection Let’s explore this Cartoon to find out… • Take a minute to read the cartoon that was just handed out. • When you are through reading the cartoon, turn it over to indicate that you have read it. Based upon your reading, does fitness always mean “the biggest, fastest and strongest”? No. The “fit” cricket has adapted a strategy for reproducing without the “cost.”

29. Mechanism: 4. Natural Selection Natural Selection: Adaptations • Adaptations: Come in many forms and help the organism survive. It could be: • Behavioral: Behaviors that an organism does to survive • Functional: An adaptation in which one aspect of the organism has increased function in an environment • Structural: Physical features on an organism that enable it to survive.

30. Mechanism: 4. Natural Selection Q: The following are examples of what type of adaptation? • Katydids blending in with their substrate. • Structural • A bird’s mating call • Behavioral • A protein working at human body temperature and denaturing at higher temperatures. • Functional

31. Mechanism: 4. Natural Selection Q: The following are examples of what type of adaptation? • Echolocation in bats searching for food • Behavioral • A bird’s beak • Structural • The non-poisonous milk snake has a banding pattern similar, but not the same as a poisonous coral snake. • Structural: This is mimicry!

32. Mechanism: 4. Natural Selection What about odd features that don’t seem to serve any selective function? • Vestigial Structures • A feature that an organism inherited from its ancestor but that is now functionless and usually less elaborate than in the ancestor. • Formed when a lineage experiences a different set of selective pressures than its ancestors, and selection to maintain the elaboration and function of the feature ends.

33. Mechanism: 4. Natural Selection Misconceptions about Natural Selection • It is not “Survival of the Fittest;” really it is “Survival of the ‘fit enough’” • Recessive alleles for disease can stay unnoticed in a population • Organism does not choose • Perfection is not obtained • Deleterious Genes: • Sickle Cell Trait

34. Evolution in Action: Coevolution Coevolution • A process in which two or more different species reciprocally effect each other’s evolution. • For example, species A evolves, which causes species B to evolve, which causes species A to evolve, which causes species B to evolve, etc A B Coevolution is the evolutionary “arms race”

35. Evolution in Action: Coevolution Types of Coevolution • Predator/prey and parasite/host • Competitive species • Mutualistic species • Like plants and pollinators