The Theory of Evolution

1. TheTheory of Evolution

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

4. The Definition of Evolution Evolution is…. • Descent with Modification • Small-scale evolution: Changes in gene frequency in a population from one generation to the next. (microevolution) • Large-scale evolution: The descent of different species from a common ancestor over many generations. (macroevolution)

5. In this example, what exactly is being modified? Which of these represents descent with modification? Phenotypic traits of a population are modified over time. This is measurable as changes in “allele frequencies” Big Beetles go through a drought and have limited food Next generation is physically smaller due to lack of food or 90% of the beetles have the gene for green color 30% of the beetles have the gene for green color

6. Let’s further study how allele frequencies can change in an activity called “Breeding Bunnies” A change in allele frequencies in a population is evidence of microevolution

7. Basic requirements of Micro-evolution • There is variation in traits.(diversity) • There is differential reproduction. Due to selective forces in the environment, not all individuals get to reproduce to their full potential. • There is heredity.

8. How do populations introduce variation or diversity? • Mutation • A change in a DNA sequence • usually because of errors in replication or repair. • Mutation is the ultimate source of genetic variation.

9. How do populations introduce variation or diversity? • Migration (Gene Flow) • Individuals from one group move into another group. • Brings in new genes or changes frequency of genes in the population. gene flow

10. How do populations introduce variation or diversity? Let’s consider the following game of chance to find out 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. But does genetic drift always increase diversity?

11. Genetic Drift: A game of chance How does the diversity of the 4th generation compare to that of the starting population? The variation has __________ in response to selective pressures • 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: decreased

12. What effect does genetic drift have on smaller populations? • Genetic drift acts faster and has more drastic results in smaller populations. This effect is particularly important in rare and endangered species.

13. 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

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

15. Driftworm Activity • Turn your intNBto the driftworm activity, and get out: • Five colored pencils • Color in Generation 0 of your driftworms

16. Driftworm Activity • Each of these worms reproduces asexually • The population size is constant • The generations do not overlap • These are haploid organisms

17. Driftworm Activity • Roll the die. • This number represents which worm survives (by chance)and can be colored in for the next generation. • Do this four more times.

18. Driftworm Activity • Repeat this in as many generations as possible • That is, until there is only one phenotype “fixed” in the population.

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

20. Genetic variation (diversity) is required for what micro-evolutionary process?

21. 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.

22. Natural Selection fittest It is often called “survival of the _________.” “Fit” often refers to a phenotype’s success in reproducing. But… is this term accurate? Is it always the biggest, fastest, strongest? Let’s read a cartoon about natural selection to find out…

23. Types of Selection • Artificial Selection: • People choose plants and animals with desirable traits to reproduce. • Nature does NOT select.

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

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

26. Types of Selection • Disruptive Selection: • Selection that favors the extremes of the distribution

27. Overview of the types of selection

28. 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

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

31. 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. What about odd features that don’t seem to serve any selective function? Vestigial Structures • An inherited feature that is now functionless and usually less elaborate than in the ancestor. • Formed when a species experiences a different set of selective pressures than its ancestors, and selection to maintain the elaboration and function of the feature ends.

33. 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

35. Coevolution • A process in which two or more different species reciprocally effect each other’s evolution. • species A evolves, which causes species B to evolve, which causes species A to evolve, which causes species B to evolve, etc. • For ex. Co-Evolution of Computer – virus A B

36. Types of Coevolution • Predator/prey and parasite/host • Competitive species • Mutualistic species • Like plants and pollinators

37. Macroevolution(Speciation) • Form of large-scale evolution • Descent of different species from a common ancestor What evidence is there for macroevolution?

38. 1. Fossil Record

39. 2. Geographic Distribution of Living Species

40. 3. Homologous Body Structures

41. 4. Vestigial Organs

42. 5. Similarities in Early Development

43. Mechanism of Macroevolution For macroevolution to occur, two populations must be reproductively isolated (or separated) from one another Green blends in with grass Brown blends in with tree trunks The separated population experience different selective pressures Over time, they evolve in separate directions, into different species that cannot interbreed

44. What is a species? Two populations that can mate and produce fertile offspring. Ex. donkeys and horses are considered different species because they produce mules, that are not fertile. But… all breeds of dogs are the same species “mutts” are still fertile

45. Does speciation occur gradually or suddenly? • Punctuated Equilibrium: • Species stay relatively unchanged over time • Speciation is driven by major events that drastically change the environment, forcing rapid evolution • Evolution occurs in rapid bursts, as supported by gaps in the fossil record. • Gradualism: • Phenotypic changes due to evolution accumulate slowly over time • Speciation occurs gradually

46. Does speciation occur gradually or suddenly? • Speciation occurs both gradually and punctually • There is evidence to support both ideologies