Natural Selection

1. Natural Selection Or, how did we get here….

3. Natural Selection • The Theory of Natural Selection is so simple that anyone can misunderstand it…. (Anonymous) • Charles Darwin (1809-1882) saw three problems in need of a solution. • Darwin was not the only one to see these problems BTW • Other ‘Naturalists’ were struggling with the same issues

4. Problem the First • There is change over time in the flora and fauna of the Earth • What we would commonly call ‘evolution’ today • The fossil record showed this to be pretty clear, even to people in the mid 1800s • This was not controversial in Darwin’s time, and is not now.

5. The Second Problem • There is a taxonomic relationship among living things • People were big into classifying stuff • It was pretty obvious that there was a relationship between different species • Different birds, different grasses, different cats etc

6. The Third Problem • Adaptation • Different kinds of teeth for different animals, say carnivore ripping teeth and herbivore grinding teeth • Different tissues within species • Heart vs. eye etc.

7. The Solution! • Natural Selection provides a mechanistic account of how these things occurred and shows how they are intimately related. • It is one of those ‘oh man is that ever easy, why didn’t I think of that?’ type things.

8. How’s it work? • There is competition among living things • More are born or hatched or whatever, than survive and reproduce • Reproduction occurs with variation • This variation is heritable • Remember, there was NO genetics back then, Chuck knew, he just knew…. • Realized that is wasn’t ‘blending’

9. How’s it Work? • Selection Determines which individuals enter the adult breeding population • This selection is done by the environment • Those which are best suited reproduce • They pass these well suited characteristics on to their young

10. How’s it Work? • REPRODUCTION is the key, not merely survival • If you survive to be 128 but have no kids, you are not doing as well as I am • I have reproduced… • Assuming the traits that made me successful will help them then I amore fit NOW than the 128 year old guy

11. This lecture keeps evolving….. • Survival of the Fittest (which Chucky D NEVER said) means those who have the most offspring that reproduce • So, the answer to the trilogy of problems is: • ‘Descent with modification from a common ancestor, NOT random modification, but, modification shaped by natural selection’

12. Different types of selection • Directional Selection • What most of us think about when we think about selection • An extreme value is selected for • Human brain size is a nice example

13. Different kinds of selection • Stabilizing or Normalizing selection • The middle is selected for • Many examples here • Symmetry • Two eyes

14. Different kinds of selection • Disruptive selection • Extremes are selected for • Might be where the two sexes come from • Trait was probably gamete sized • Two ‘mating types’

15. But… • Darwin was troubled by the preponderance of behaviour that seemed to be of no benefit to the actor • Examples • Sterile insect castes • Bee stings • Alarm calling • Reproductive restraint

16. Reproductive restraint • Birds can produce many more eggs than they actually do! • Wynne-Edwards beleied that selection also acted on the species level to stop massive overpopulation

17. Reproductive Restraint? • Lack argued that animals are doing what is best for the INDIVIDUAL • Big clutch means possible exhaustion, death • LIFETIME fitness, not just this season

18. Lack • Well, if clutch size depends on the environment, then clutch size should vary with quality of resources

19. Hamilton figured it out • Hamilton’s Response was theoretical • Look at behaviour from the gene’s point of view • Inclusive fitness = direct fitness + effect on fitness of others

20. Hamilton • C < rb • Or r > c / b • Remember, r is relatedness, c is cost b is benefit • Would you give your life for a brother? • No, but maybe 2 brothers, or 8 cousins • Two uncles and one mother….

21. Mechanism • For this to work there must be some sort of proximate mechanism • Easy for mother/father and child • How about everyone else? • ‘Green Beard’ hypothesis • Allele produces some phenotype • Also allows for recognition • Tough for a single gene….

22. The elusive mechanism • Proximity • Families • Little dispersal • So if close by, you are related • Example: • Leaf eating ants • Far nests  more hostile • Different plants  more hostile

23. More on mechanism • Those crazy ants • Split colony and put on different plants • Hostile, but non injurious! • Gene environment interaction baby! • Vervet monkeys • 2 year olds scream • Mother comes • Others watch the mother!

24. Mechanisms, pheremones and bees • Greenberg looked at bee relatedness and allowing bees in or not • Probably genetically determined odour

25. Conclusions about inclusive fitness • Group selection is silly • Individual selection is cool • Gene level selection is VERY cool • Hamilton is a genius • Don’t over use this • Gives us some insight into some nasty human behaviour

26. Games are fun • Animals tend to behave in ways that maximize their inclusive fitness • Usually pretty straightforward • But, sometimes we must know what others are doing before we adopt a strategy • What if your mating call is drowned out by others’ calls, what to do, ahh what to do…

27. Fitness and Strategies • In certain cases payoffs, and hence fitness maximization, depend on what other populations are doing • When the payoff to one individual depends on the behaviour of others we cannot use the principle of fitness maximization until we know: • What the alternatives are • P(encountering alternatives) • Consequences of encounter

28. Game Theory • Think of it like a game • Each individual’s behaviour is its strategy, payoffs are in units of fitness • Players produce more players (offspring) • Changes in fitness are directly proportional to payoffs • An evolutionary Stable Strategy is one that, when adopted by enough individuals, maximizes payoff

29. Pure Strategy • One that cannot be replaced • Food storing • Recover your own seeds (Anderssen and Krebs, 1978) • If they recovered communally, a selfish hoarder would replace the communals damned quckly

30. Mixed Strategies • Hawks and Doves • Not real hawks or doves, strategies • Always fight, or always give up • Look at the payoffs • Look at the costs • Determine what proportion should be hawks and should be doves

31. Hawks and Doves • Say its all Doves • Hawk shows up, wins resource • Spreads genes • Now more hawks • Oh oh, now you are fighting, P(injury) = .5 • Now being a dove pays • Either strategy good when rare, bad when common

32. Doves and Hawks • V = Value of resource for winner • W = cost of a wound • T = cost of display (no fighting) • (John Maynard Smith, 1978)

33. Whoa, I know Kung Fu • Set up a payoff Matrix Opponent in the contest Hawk Dove Payoff Hawk ½(V-W) V Received By Dove 0 ½V-T

34. ESS as easy as 123 • If W > V then there can be no pure ESS • In a population of hawks, a small number of doves do better than hawks • E(dove,hawk) > E(hawk, hawk) • E(dove, hawk) = 0 • E(hawk, hawk) = ½(V-W) • W > V, therefore ½(V-W) < 0

35. Pure Doves don’t do it either • Payoff to Hawk is V • Payoff to doves is less than that • (½W – T) • Hmmm • So, what proportion of hawks and doves balances it out?

36. What is theoretical population biologist to do? • Find the proportion (p) of hawks of hawks such that the following equation balances: • p ½(V-W) = (1-p) V = p (0) + (1-p) (½V– T) • Simply (?) solve for p • p = (V+2T) / (W+ 2T)

37. Apply it, sort of • Say V = 10 • W = 20 • T = 3 Opponent in the contest Hawk Dove Payoff Hawk -5 10 Received By Dove 0 2

38. Now, sub that back into the formula • P = 16/26 or 8/13 • 8/13ths of the population, with these payoff values, must be hawks • The values are not that important really, the point is that you can determine the point at which a strategy can coexist with another strategy as an ESS • Could be percentage of population, or percentage of time each animal adopts a given strategy

39. So? • It is actually applicable that’s so • Toads looking for breeding grounds (Davies and Hallaway, 1979) • Payoffs determined

40. Another so • Dungflies • Should a male hang around poo as it gets older?

41. Conclusions • This is a very brief intro to game theory • This stuff is way powerful • You have to sit and think some about the payoffs and costs • Dynamic programming models are becoming more popular

42. Other Evolutionary Theories • Lamarckism • Inheritance of acquired characteristics • E.g., giraffes really wanted leaves, so they stretched their necks and….. • Sounds crazy, but a lot of people think this way • ‘We will all have giant heads and tiny bodies someday’ • ‘Cave swelling fish don’t use their eyes so they disappear’ • ‘We don’t use our appendix so it is disappearing’

43. Silly incorrect evolutionary theories and ideas • Orthogenesis • There is some plan to evolution. • NO WRONG INCORRECT, THANKS FOR PLAYING • The idea of an ‘evolutionary ladder’ fits in here • It is wrong too……

44. Still another silly idea • Intelligent Design • Just Creationism with a fancy name • God does not belong in a science class, any more than experiments belong in church • NOT A SCIENTIFIC THEORY