Evolution Lecture 4: Natural Selection I

1. Evolution Lecture 4: Natural Selection I

2. Theory of EvolutionHistory • Famously credited to Charles Darwin • Was independently discovered by 3 other people • https://www.youtube.com/watch?v=xJFBSoJE67I -Alfred Wallace being the best known other • How did Darwin arrive at this theory?

3. Artificial Selection We already discussed dogs/foxes experiment Darwin bred pigeons, artificially selected for phenotypes (visible traits of an organism) Can also see in agriculture tomatoes

4. Domestic vs. Wild Tomatoes • Size differences controlled by gene fw2.2 • Protein that suppresses cell division of fruit • Changes in the DNA code for that gene can alter how much of the protein is made • Wild tomatoes make a lot, domestic a little

5. Experiment inserting the wild small fruit gene copy (the allele) into a domestic tomatoes results in fruits ~30% smaller Natural populations will have some variation for these alleles that control fruit size Early farmers could choose to plant seeds from largest tomatoes, selecting for larger fruits over time

6. Brassica oleraceaAll the same species!

7. Why aren’t these traits seen in wild populations? It can happen, but many of the traits selected for by humans would be disastrous in wild populations! 5th generation farmed salmon are only 16% as successful at breeding when released compared to wild salmon

8. What we do see in the wild:Natural Selection KEY COMPONENTS: 1. Variation is present 2. Variation is heritable 3. More individuals are born than can survive 4.Some variants survive & reproduce more than others

9. Heritable traits conducive to survival and reproduction are passed to offspring at higher rates, becoming more and more common in a population; those conducive to death are less likely to be passed to offspring (bc…you’re dead) and they become more and more scarce. Populations thus change gradually over generations. Remember, individuals survive/reproduce (are what selection act on), but populations are what change (evolve)! https://www.youtube.com/watch?v=R6La6_kIr9g

10. Individuals with advantageous traits are naturally selected for survival, just as a farmer can artificially select a tomato But in natural selection, there is no intent or goal! There are only individuals with traits that naturally confer an advantage to survival and reproduction.

11. Population of white-tailed deer • Some have slightly longer legs, some shorter • Road is built through habitat • Long legged deer better able to avoid cars!

12. Population of white-tailed deer shifts to longer legged individuals surviving & reproducing • The average leg length of this population increases over time…long legged deer have higher fitness

13. Darwinian fitness Fitness-individual’s ability to survive & reproduce This may not relate to physical fitness Gulls with high phyical fitness did not have high Darwinian fitness

14. Adaptation Adaptation-a trait that increases an organism’s fitness relative to individuals lacking it Such a trait is said to be adaptive Example: Darwin’s moth and orchid Videos: https://www.youtube.com/watch?v=Q8GdkMBluis https://www.youtube.com/watch?v=iMz6lApJgu4 https://www.youtube.com/watch?v=VUiZDhs0JrA

15. Examples Natural Selection Do bumblebees drive evolution of snapdragon flower color? • Population of snapdragons have white and yellow flowers • Flower color is controlled by an inherited gene • Researchers ensured survival of plants, but not reproduction, allowed bumblebees to control that naturally • White plants reproduced better than yellow

16. Examples Natural Selection

17. Beak Shape of Finches Galapagos finches (13 species) Around 4-6 inches in size Beaks vary dramatically! Eat different foods based on beak shapes

18. Medium Ground Finches 1. The birds vary in multiple phenotypic traits (wing length, beak size, tail length, etc.) 2. Is this variation heritable (vs. nurture/environment)? Examined parents and offspring, beaks sizes are heritable/+ genetic studies showing this as well 3. Drought showed that there are differences in survival among the finches, population size declined 4. Those that survived had larger beaks (eat big seeds)

20. Evolution Lecture 5: Natural Selection II

21. Important Points Concerning Natural Selection • Evolution is a statistical process of changing frequencies • Natural Selection acts on individuals, but the consequence is on population • Individuals live, die, reproduce or don not reproduce • Frequencies of traits (or alleles) change through the population • Nat. sel. acts on phenotypes, but evolution consists of changes in allele frequencies • If phenotypes are determined only by the environment, then we would not expect changes in allele frequencies. Therefore, selection acting on phenotypes determined by the environment would not produce any expected changes in the next generations

22. Selection is not forward thinking • It is not goal oriented • Selection cannot anticipate environmental changes • Evolution is always a generation behind any changes in the environment

23. Selection only acts on existing traits, although new traits can evolve • Natural selection only acts on variation present in populations • New traits can evolve: • Mutation adds new variation • Sexual reproduction can provide new combinations of alleles

24. Oil content in original 163 ears of corn was determined 2. 24 ears of corn were chosen for the highest oil content each generation 3. After 60 years a new range of oil production was observed that did not overlap with the original 163 plants

25. Preadaptation • A trait that is used in a novel way and eventually elaborated into a new structure • An unpredicted function for an existing structure • It improves an individuals fitness fortuitously---not because natural selection is goal oriented

27. Natural Selection is not perfect • It results in adaptations • These adaptations are not always perfect • Birds with deeper beaks also have wider beaks • Deeper beaks are great for applying downward force to crush large nuts • Wider beaks are not good for producing twisting forces that also crack open nuts. • Birds with narrow beaks also survived the droughts

28. Natural selection is nonrandom, but not progressive • The results of selection are not random, they lead to adaptations • It is free of an entities’ conscious intent • It is not progressive…they only increase adaptation • There is no trend toward more advanced life forms • Adaptations can lead to a reverse in complexity (e.g., snakes limblessness and birds lack of teeth)

29. Fitness is not circular • It appears that it is obvious that individuals with favorable variations are the ones that survive, b/c the theory defines favorable as the ability to survive • The only requirement is that some variants do better than others, as opposed to random ones

30. Selection acts on the individual and not for the good of the species • Self-sacrificing, altruistic behaviors do not occur in nature---except in the instances of kin selection • An allele that would reduce the bearers fitness while benefitting unrelated individuals would be strongly selected against • Actually, altruistic behavior occurs when individuals are genetically related (prairie dogs) or beneficiaries reciprocate (nursing lions). • Infanticide provides evidence against altruism (lions)

31. Problems with accepting evolution until 70 years after the introduction of the theory • Had no idea how variation was created • Natural selection grinds to a halt w/out variation • Morgan showed in the early 1900s that mutation creates variability in every trait in every generation • Had no idea about heritability • Believed in blending..not true • Did not know about Mendel’s work…discovered 35 yrs after his publication • Lord Kelvin published papers that the earth was only 15-20MYO..not enough time for evolution to produce all of the creatures on the planet • Earth’s heat is due to radioactive decay, not radiant cooling, and that the sun’s energy is from nuclear fusion and not combustion

32. Problems with accepting evolution until 70 years after the introduction of the theory Video on Mendel/selection https://www.youtube.com/watch?v=WhFKPaRnTdQ

33. Modern Synthesis • Between 1932-1952, a series of groundbreaking books successfully integrated Darwin’s ideas with genetics. This created modern statistics and population genetics • Gradual evolution results from small genetic changes that are acted on by natural selection • The origin of species and higher taxa, (macroevolution) can be explained in terms of selection acting on individuals, microevolution • https://www.youtube.com/watch?v=gD_-j9LfaQM&t=7s

34. Darwin’s four postulates in terms of the modern synthesis • As a result of mutation creating new alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals are variable for many traits • Individuals pass their alleles on to their offspring in tact • Some individuals are better at surviving in every generation • The individuals that survive and reproduce, or who reproduce the most, are those with the alleles and allelic combinations that best adapt them to the environment.

35. Arguments against evolution • Scientific Creationism • Intelligent design and the blind watchmaker • Biochemical design and irreducibly complex structures (flagella and cilia composed of 6 proteins that must be present for motion to work) • Evolution by natural selection is not falsifiable and makes no predictions • Not enough time to create all species by evolution 6000-8000 yrs ago • Organisms evolve from simple to complex, this violated the second law of thermodynamics (entropy increases in a closed system) • No one has witnessed evolution and the formation of new species (apple maggots, inference) • Controversy motivated by morality issues, money and/or selection preservation of a religious industry • Video all about it : https://www.youtube.com/watch?v=P3GagfbA2vo