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Evolution: How species have changed over time

Evolution: How species have changed over time. First a Perspective of Time. Those who influenced Darwin. 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.

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Evolution: How species have changed over time

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  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

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

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

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

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

  9. 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

  10. Result 1. Competition • What are we competing over? • Who wins? What is the prize? • What happens to those that don’t win?

  11. Result 2. Survival of the Fittest • In nature are we all really equal? • What do we mean by “fittest”? • Is it enough to survive?

  12. Result 3. Descent with Modification • Break it up, what does it mean? • What happens to the frequency of fit genes and unfit genes? • What do we see in future generations?

  13. 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)

  14. An Example

  15. 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?

  16. Rules of Evolution • Mutations and their phenotypes are random. Meaning? • Variation must exist in the population BEFORE selective pressure occurs

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

  18. 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?

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

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

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

  22. 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

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

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

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

  26. Examples: Offspring: Mule! Viable but infertile

  27. 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

  28. 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

  29. 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!

  30. Phylogenetic tree: Family Tree of Life

  31. 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?

  32. Evidence of Common ancestry • Comparative Anatomy • Comparative Embryology • Comparative Biochemistry • See Determining evolutionary relationships assignment

  33. Evidence of a Universal Common Ancestor • What do we ALL have in common

  34. 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!)

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

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

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

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

  39. Radioactive material decays into a non-radioactive decay product at a steady rate. • Half life = time it takes half a sample to decay.

  40. Example: Some carbon is naturally radioactive – C14. Half life of C14 – 5,730 years Decay product is N14 If we look at the sample and determine the ratio of C14 to N14 we can get an idea of how much time has passed

  41. Assume we start with a sample that is 100g of C14

  42. Geographic Distribution • Biogeography and Convergent Evolution: • See Determining evolutionary relationships assignment

  43. 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.

  44. Vestigial Organs • Gives insight into PAST needs of organism as well as where this organism has come from • What happens first: • Need for organ disappears? • Or mutated organ appears?

  45. Genetics in Evolution Darwin did his work before Mendel and didn’t understand genes or how inheritance worked. Thanks to Mendel we know how/why traits get passed from parent to offspring

  46. Phenotypes NOT genotypes • Natural selection acts on phenotypes NOT genotypes But in turn will influence allele frequency. Why aren’t all bad alleles eliminated??

  47. Mechanisms of Evolution • Remember, it is variation that proposes and selection that disposes

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