Evolution: A Historical Perspective on Species Changes

1. Evolution: How species have changed over time

2. First a Perspective of Time

3. Those who influenced Darwin

4. Charles Darwin • Was a Naturalist – mostly observed organisms in their natural habitats rather than conducting experiments. • Made most of his observations on the Galapagos Islands

6. Charles Darwin • Did much of his work in the Mid-1800’s ** Keep in mind this is BEFORE Mendel, Watson and Crick***

7. Charles Darwin • Introduced the idea of Natural Selection as a way for new species to form (speciation). • Published The origin of Species in 1859

8. The Theory of Natural Selection • Assumptions: • There are not enough resources for all to survive • genetic variationexists in all populations. Results: • Competition • Survival of the fittest • Descent with modification

9. Assumption 1: Not enough resources • What resources are we talking about? Suitable Mates Food Shelter • Are there enough for everyone?

10. Assumption 2: Genetic variation exists • Where do these differences come from? Sexual reproduction Genetic Recombination Mutations Migration • Remember it doesn’t have to be a NEW gene, just a new combination of genes

11. Result 1. Competition • Individuals will compete for the limited resources. • Goal is to survive and pass on genes • “winner” gets to pass genes on at higher rate.

12. Result 2. Survival of the Fittest • Not all variations are equal. Some are better at competing in their environment than others. These individuals are more likely to “win” and survive to pass on their genes. • Fitness: an organisms ability to survive and reproduce.

13. Result 3. Descent with Modification • Descent – To come from • Modification – With changes • More of the “fit” genes will be passed on than “unfit” • In future generations, the frequencyof fit genes increases, while the frequency of unfit genes decreases.

14. 3. Descent with Modification • New generations will resemble previous generations (descent) BUT more individuals will have the “best” variation PLUS new mutations and combinations (with modification)

15. An Example

16. Example: • What is the genetic variation? • What is the selective pressure? • Who has the advantage? • What would we predict for the next generation? • Why might the “unfit” phenotype stick around?

17. Rules of Evolution • Mutations and their phenotypes are random. Meaning? • Variation must exist in the population BEFORE selective pressure occurs • If no “fit” variation exists when pressure begins, entire population dies = Extinction

18. Rules of Evolution • Individuals can not evolve, only species • A fit trait in one environment might be eliminated as a weakness in another

19. Types of Selection • Natural Selection • What determines which variation gets passed on? • What is the outcome? • Artificial Selection (a.k.a. selective breeding) • What determines which variation gets passed on? • What is the outcome?

20. Types of Selection Directional Selection: One extreme or the other is “favored” and increases in frequency while midrange and other extreme decrease

21. Types of Selection Stabilizing Selection: Midrange is favored and increases in frequency while both extremes decrease.

22. Types of Selection Diversifying/disruptive Selection: Both extremes are favored and increase while midrange decreases.

23. At what point is a new species formed? • Evolution – change in allele frequency • Speciation – such change that new population is a different species – two organisms that can successfully reproduce and produce viable, fertile offspring

24. Examples: Cross between a Pug and a Beagle - different breeds but SAME species

25. Examples: Offspring: Puggle! Both viable (obviously) and fertile

26. Examples: Cross between a Horse and Donkey - different species

27. Examples: Offspring: Mule! Viable but infertile

28. Gene Pool Isolation • Two populations become separated so their genes are no longer mixed • Mutations appear independently in each population • Selection happens independently in each population

29. Mechanisms of Isolation • Geographic – Physical barrier separates two populations • Behavioral – mating behaviors of some are not attractive to others. • Temporal – fertility occurs at different times • Mechanical – different physical means of reproduction

30. Principle of a Common Ancestor • Descent with Modification – over generations descendents can look quite different from ancestors. • Thus, organisms that seem very different might share a common ancestor • Suggests if you go far enough back, we are all related!

31. Phylogenetic tree: Family Tree of Life

32. Common ancestor • Humans and chimps have a common ancestor. • THAT IS NOT THE SAME AS SAYING WE WERE ONCE CHIMPS!!! • Think about it: Do you and your cousin share a common ancestor? Does that mean you are your cousin? Does that mean that either of you are that ancestor?

33. Evidence of Common ancestry • Comparative Anatomy – examining body parts • Homologous structures – similar in form, but not necessarily function; • suggests common ancestor • Results from divergent evolution

34. Evidence of Common ancestry

35. Evidence of Common ancestry • Comparative Embryology – examining developmental patterns • Similar organisms follow similar developmental patterns • We all start off the same – a single egg • BUT the series of steps that follows is most similar between closely related organisms

36. Evidence of Common Ancestry

37. Evidence of Common ancestry • Comparative Biochemistry – examining DNA and protein sequences • Remember: DNA contains info to make proteins. Proteins are responsible for our traits. • Organisms with close ancestors share a large percentage of DNA.

38. Evidence of Common ancestry

39. Evidence of a Universal Common Ancestor • All life is cellular • All life encodes its information in nucleic acids • (DNA/RNA) • All life shares the same genetic code • (AUG = Met)

40. Evidence of a Universal Common Ancestor • All Life uses ATP as its energy molecule • Suggests we are all derived from the same thing and that thing had all these traits!

41. Additional Evidence of Evolution (but not necessarily common ancestry) • Fossil Record • Vestigial organs • Biogeography • Analogous traits • Convergent evolution

42. Additional Evidence of Evolution (but not necessarily common ancestry) Fossil Record • Preserved remains of ancient life in sedimentary rock • Even of species no longer in existence (most!)

43. Fossils • Fossils are often found in the layers of sedimentary rock. • See changes in fossils over time

44. Dating Fossils • Absolute Dating: • Using radioactive organic material in a sample we can get a more accurate age of a fossil

45. Dating Fossils • Relative Dating: • Fossils found in lower levels are older than upper levels. • Can’t provide exact age, just which is older

46. Dating Fossils • Absolute Dating: • Radioactive organic material is used to get a more accurate age of a specimen.

47. Geographic Distribution • Biogeography – study of the distribution of plants and animals throughout the world and their climates • Convergent Evolution: Unrelated organisms exposed to same environmental pressures may develop similar traits to cope with those pressures

48. Analogous Structures • May serve same function, but are structurally different and did NOT come from a common ancestor • Evolved independently

49. Vestigial Organs • Structures that serve little to no purpose NOW • Snake skeletons with leg bones and pelvis • Blind, cave-dwelling fish have eye-sockets but no eyes.