Darwin’s Voyage of Discovery

1. Darwin’s Voyage of Discovery Section 16.1

2. Darwin’s Epic Journey • Evolution – process of change over time • Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors

3. HMS Beagle • Darwin collected specimens of plants and animals • The idea of evolution shows how the living world is constantly changing • Darwin noticed three distinctive patterns of biological diversity • Species vary globally • Species vary locally • Species vary over time

4. 3 distinctive Patterns • Species vary globally • Different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe • Species vary locally • Different, yet related, animal species often occupied different habitats with a local area • Species vary over time • Some fossils of extinct animals were similar to living species

6. Tortoises

7. Ideas that Shaped Darwin’s Thinking Section 16.2

8. An Ancient, Changing Earth • James Hutton and Charles Lyell-Earth is extremely old and processes that changed Earth in the past are the same processes that operate in the present • Concluded that our planet must be much older than a few thousand years • If geological phenomena like volcanic eruptions and earthquakes could transform Earth’s surface *so it* could change over time, so could life on Earth *add to notes

9. An Ancient, Changing Earth CONT. • Lamarck’s Evolutionary Hypothesis • Jean Baptiste De Lamarck suggested two of the first hypotheses on evolution • Organisms could change by use or disuse of various parts of their bodies • Individuals pass these acquired traits, enabling species to change over time

10. Lamarck’s Ideas • All organisms have an inborn urge to become more complex and perfect • Ex: Ancestors of birds develop wings bc they had the urge to fly • Structures of individual organisms could also change if they were not used • Ex: Long legged birds, legs become shorter if they don’t use the length • Acquired traits are passed from parent to offspring-inheritance of acquired characteristics • Ex: Giraffe necks become longer because parents stretch towards leaves

12. An Ancient, Changing Earth CONT. • Today we know that Lamarck’s hypotheses were incorrect in several ways. • Organisms do not have a drive to be more perfect • Evolution does notprogress in a predetermined direction • Traits acquired by individuals during their lifetime cannot be passed on to offspring

13. Population Growth • Thomas Malthus-if the human population grew unchecked, there wouldn’t be enough living space and food form everyone • Forces working against population growth include: war, famine, and disease • This lead Darin’s realization that most organisms don’t survive and reproduce • Poses the questions: Which individuals survive, and why?

14. Artificial Selection • Darwin studied change produced by plant and animal breeders • Variation seen in organisms could be passed from parents to offspring, and used to improve crops and livestock • Overtime, this selective breeding would produce organisms with desirable traits; this is known as artificial selection

15. Darwin Presents his Case Section 16.3

16. Evolution by Natural Selection • Natural selection-organisms with variations suited for the environment survive and reproduce more • If more individuals are produced than can survive, a population competes for food, living space and other limited resources • Individuals have natural variations among their heritable traits, some traits are better suited to life in their environment • Adaptation - inherited characteristic that increases an organism’s ability to survive and reproduce

17. Natural Selection CONT. • Survival of the fittest – individuals with adaptations that are well suited to their environment can survive and reproduce • Fitness – how well an organism can survive and reproduce in its environment • Different from artificial selection because nature, not man, influences fitness

18. Natural Selection must have: • Struggle for existence • Variation and adaptations • Competition to survive and reproduce • Survival of the fittest • Change over time to become better suited for their environment • It does not move in a particular directions • Does not make an organisms “better”, just increases the chance of passing genes to the next generation

19. Struggle for Existence Variation and Adaptation Natural Selection Survival of the Fittest

20. Common Descent • Natural selection depends on the ability to leave descendents. Darwin proposed that over many generations, adaptation could cause successful species to evolve into new species • Descent with Modification – living species are descended, with modification, from common ancestors • Common descent – all species, living and extinct, are descended form ancient common ancestors

21. Evidence of Evolution Section 16.4

22. Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors

23. Age of Earth and Fossils • After Darwin published his theory, physicists discovered radioactivity • Radioactive dating indicates that the Earth is about 4.5billion years old, plenty of time for evolution to occur • Many recently discovered fossils form series that trace the evolution of modern species from extinct ancestors • There are many missing fossils and the fossil records are incomplete

24. Evidence From Fossils

25. Comparing Anatomy and Embryology • Many physical structures can be compared to look for evolutionary relationships • Homologous structures – structures shared by related species and that have been inherited from a common ancestor • Ex: bat wing, alligator forelimb, chicken wing, human hand, whale fin

26. Comparing Anatomy and Embryology CONT. • Analogous structures – structures that share common functions, but not structure • Ex: insect wing vs. bird wing • Vestigial structures – structures inherited from ancestors but have lost much or all of their original function • Ex: whale’s hipbones

27. Comparing Anatomy and Embryology CONT. • Similar patterns of embryological development provide further evidence that organisms have descended from a common ancestor • Ex: different adult shapes, but all the bones develop from the same clump of embryonic cells

28. Genes and Variation Section 17.1

29. Genetics Joins Evolutionary Theory • In any population, some phenotypes may be better suited to their environment than others. Since better-suited individuals produce ore offspring, they pass more copies of their alleles to the next generation • Ex: peppered moths • Remember, natural selection acts on an entire organism, not specific genes

30. Populations and Gene Pools • Genetic variation and evolution are both studied in populations • Population – group of individuals of the same species, in the same area that can mate • Genetic variation – variation in alleles of genes among members of a population

31. Populations and Gene Pools CONT. • Members of a population share a common group of genes called a gene pool • Gene pool – all the genes of a population • Each gene pool contains a number of alleles • Relative frequency is 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 • Expect alleles for successful traits to have higher relative frequencies

32. Allele Frequency • Allele Frequency for B-black = 40%  20/50 x 100 = 40% • Allele Frequency of recessive b-brown = 60% 30/50 x 100 = 60%

33. Populations and Gene Pools CONT. • Evolution, in genetic terms, involves a change in the frequency of alleles in a population over time

34. Sources of Genetic Variation • Genes are the carriers of inheritable characteristics and a source of random variation • Variations caused by: • Environmental factors • Heredity

35. Sources of Genetic Variation CONT. • Environmental factors • Amount or quality of food, water • Weather • Heredity • Genotype & Phenotype • Mutations – any change in the genetic material of a cell • Genetic recombination occurs during meiosis

36. Single-gene vs. Polygenic Traits • Number of phenotypes produced for a trait depends on how many genes control the trait • Single-gene trait – trait controlled by only one gene • Ex: all of Mendel’s pea characteristics – color, height • Polygenic trait – trait controlled by two or more genes • Ex: height, weight, eye color

37. Evolution as Genetic Change in Populations Section 17.2

38. How Natural Selection Works • Evolutionary fitness is measured by how many genes are passed to the next generation • Natural selection on Single-gene traits • Can lead to changes in allele frequencies and, thus, to changes in phenotype frequencies • Ex: lizard color – normally brown, mutants are red or black. Red are more readily seen by predators and black may warm more quickly and avoid predators

39. How Natural Selection Works CONT. • Natural Selection on Polygenic traits • Can affect the relative fitness of phenotypes and thereby produce one of three types of selection • Directional Selection • Stabilizing Selection • Disruptive Selection

40. Directional Selection • Individuals at one end of the curve have higher fitness than individuals at the other end or the middle Ex: Average beak size increases when supply of small and medium-size seeds run low

41. Stabilizing Selection • Individuals near the center of the curve have higher fitness than individuals at either end Ex:Babies with an average mass are more likely to survive than those who are very small or very large

42. Disruptive Selection • Individuals at outer ends of the curve have higher fitness than individuals in the middle of the curve Ex: medium sized seeds become less common, large and small seeds more common = birds with large or small beaks have higher fitness

43. Genetic Drift • Genetic Drift – random change in allele frequency • Ex: bottleneck effect and founder effect • Bottleneck effect – change in allele frequency following a dramatic reduction in population size • Ex: overhunting of walruses on the west coast

44. Genetic Drift CONT. • Founder Effect – allele frequencies change as a result of the migration of a small subgroup of a population • Ex. Fruit Flies on Hawaiian Islands

45. Evolution vs. Genetic Equilibrium • If a population is not evolving, allele frequencies in its gene pool do not change, this population is in genetic equilibrium • Meiosis and fertilization by themselves do not change allele frequencies. Therefore, a population could remain in genetic equilibrium forever.

46. Hardy-Weinberg Principle • Allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change • Makes predictions like a Punnett-square, but for an entire population not individuals p2 + 2 pq + q2 = 1 In words: (frequency of AA) + (frequency of Aa) + (frequency of aa) = 100% and (frequency of A) + (frequency of a) = 100%

47. Hardy Weinberg Problem • Suppose that, in one generation, the frequency of the A allele is 40% (p = .40) and the frequency of the a allele is 60% (q = 0.60). If in genetic equilibrium, chances of individual in next generation having: AA would be 16% (p2 = .402 = 0.16 or 16%) aa would be 36% (q2 = .602 = .36) Aa would be 48% (2pq = 2(.40)(.60) = .48)

48. 5 Conditions that can change Equilibrium causing evolution to occur • Nonrandom mating • Small population size • Immigration and Emigration • Mutations • Natural selection

49. *Nonrandom Mating • Individuals must mate with other individuals at random • Can’t select mates based on heritable traits

50. Immigration or Emigration • Immigration – individuals who join a population • Introduce new alleles • Emigration – individuals who leave a population • May remove alleles