Psychology 350: Human Sexuality

1. Psychology 350:Human Sexuality Spring 2010 Professor Debra Lieberman Lecture 2 Thursday, February 4th, 2010 1

2. On tap this evening Feedback on films Review of topics from last time Finish up some concepts Example of adaptation versus by-product The female orgasm Level of selection Genes as the unit of selection Kin selection as example of genic selection ESS Misunderstandings to avoid 2

3. Topics from last time Adaptationist Program Evolutionary Psychology 5 organizing principles of how to approach psychology Selection Pressures Adaptive Problems Adaptations 3

4. Time machines In this way, adaptations are like time machines, except they don�t transport us to the past, they transport information about the past to us. 4

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6. Different levels of analysisDifferent kinds of questions 6

7. Clarifying Biological Explanations:Marr�s (1982) 3 levels of explanation Functional Level (Adaptive Problem): What is the goal of the computation, why is it appropriate, and what is the logic of the strategy by which it can be carried out? Cognitive Level (Representation & Algorithm) How can this computational theory be implemented? In particular, what is the representation for the input and output, and what is the algorithm for the transformation? Hardware Implementation (Neuroscience) How can the representation and algorithm be realized physically? 7

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9. Ultimate explanations Ultimate explanation: Why is a particular feature a part of our species-typical design? How did this feature affect the probability of survival and reproduction? What were the selection pressures that brought about this feature? 9

10. Proximate explanations Proximate explanation: How does the mechanism operate in real time? Given that choosing a fertile mate was important for a male�s reproductive success, how does a male figure out who is fertile? What information is used from the world? Hormones/ chemical messengers involved in activating and deactivating behaviors How feature develops and relevant aspects of the environment. 10

11. Distinguishing adaptations and by-products: Female orgasm as an example 11

12. G.C. Williams �Adaptation� is a special and onerous concept. Use only when necessary When there is solid evidence that a given phenotypic trait is so well engineered to solve a specific problem that it couldn�t be merely a byproduct of something else. Does human female orgasm satisfy this requirement? 12

13. The Female Orgasm What would the adaptationist claim mean? That females with orgasms out-reproduced females without them because of the orgasm. Had a positive effect on fitness. 13

14. Early thinking on the orgasm Early thinking: fuzzy and vague Female orgasm �cements pair bonds.� (Who�s the beneficiary? Why does it have this effect?) �Promote marriage� by making sex more pleasurable (for women) as if one can�t have sex outside marriage? 14

15. Proposed beneficiaries were abstractions Pair-bonds, not RS of ancestral females Didn�t specify what human female characteristic was hypothesized to have been designed during the course of human evolution to promote female orgasm Genital morphology? Brain morphology? 2 reasons why these aren�t really adaptationist hypotheses 15

16. The female orgasm: A by-product? (perhaps) What would this claim mean? That this feature was not selected because it increased reproductive success. What could it be a byproduct of? Some design features �carry over� to the other sex. (e.g., male nipples. No function, but cheaper to leave them in than engineer them out.) 16

17. Comparative evidence If for pair-bonding and marriage, then perhaps unique to human females? Also might then expect it to be a universal Non-human animals Evidence for orgasm in some species Rhesus females �clutch� partners. (?) Baboon females emit a �characteristic vocalization� (?) Some chimps too. Who really knows? Humans: ethnographic data suggests that female orgasm is NOT a human universal 17

18. Engineering evidence Is female orgasm precisely engineered to achieve some reproductively beneficial goal? The physiology of female orgasm is strikingly similar to male orgasm Supports by-product hypothesis 18

19. Some data on female orgasm Study of 800 couples in 1938 22.1% always have orgasm during intercourse, 44.5% usually, 25.1% sometimes, 8.3% never. In 1956, these #�s were: 24%, 35%, 26%, 10% (rarely), 5% In 1977, these #�s were 15%, 48%, 19%, 11%, 7% 19

20. Cross-cultural data Huge variability Mead claimed the concept of female orgasm is absent in some cultures Marshall (1971) reports a culture in which �all� women experience orgasm. [Mangaia (Polynesia). Here, boys 13-14 are given formal instruction in this area] Ethnographic literature suggests: �men take the initiative and, without extended foreplay, proceed vigorously toward climax without much regard for achieving synchrony with the woman�s orgasm�� Davenport, 1977 20

21. Orgasm: evidence If it�s an adaptation, does it have features that make it good at doing something? The physiology looks like the male physiology. Recent work (Baker & Bellis) suggests that Orgasm near the time of ejaculation increases retention of sperm. No evidence of maximum likelihood of conception Given muscle contractions, not surprising that sperm is retained. For women who are having extramarital affairs, orgasms with lovers (not husbands) led to greater sperm retention. 21

22. Mr. Right Detector? Maybe it�s designed to �sort� men by competence. Thornhill, Gangestad, & Comer (1995) ��it seems reasonable to hypothesize that orgasm is an adaptation for manipulating the outcome of sperm competition resulting from facultative polyandry� Probability of orgasm increases with symmetrical males (!) (Fluctuating asymmetry index) 22

23. What a �Mr. Right� hypothesis implies There was some kind of information about men�s mate value that ancestral females could ONLY obtain by having sex with prospective mates and seeing whether they had an orgasm. Information they couldn�t have more cheaply obtained some other way That this information was beneficial ENOUGH to outweigh the costs of having sex with candidate mates. 23

24. Another way to evaluate adaptationist claims If the proposed hypothesis is correct , what OTHER adaptations ought we to expect to exist? Consider the Baker and Bellis hypothesis for selection pressures on ancestral males. What designs should we see in human males? Specialized calibration and training of technique Detection of faking? Timing 24

25. The female orgasm: Conclusions My view is that there is some evidence in favor of the view that it is an adaptation, but not sufficient evidence to make a strong claim. An important moral is that traits should be considered byproducts by default; adaptation is a strong claim, requiring evidence of design. 25

26. What is the level of selection? 26

27. What is the level of selection? Do design features (behaviors) persist because they promote the fitness of: the gene? the individual? the population? the species? 27

28. Levels of selection The idea that there is a purpose and a direction of events � teleological. Good for keeping the balance of nature Good of the planet: Gaia hypothesis plants provide oxygen for the animals Good of the ecosystem predator and prey keep each other in check Good of the species �for the survival of the species� what is the good of the species? Number? 28

29. Good of the group langurs, reproductive restraint Good of the individual approximation intragenomic conflict: kill rival gametes Good for the gene -- real answer: gene propagation Argue: Good at �higher levels� is a byproduct of being good for the gene Levels of selection 29

30. Beginning at the Beginning Let�s assume a universe. Let�s assume some things are more stable than other things. By definition, stable things will persist longer than others If you go away, and then come back, you�ll tend to see stable things. One kind of stability is making copies. Things that have the property that they make copies of themselves are called �replicators.� 30

31. Replicators Let�s assume there are lots of different kinds of replicators. Given this assumption, some are going to replicate faster than others. Now assume copying errors (mutations). Errors that cause the replicator to decrease its replication rate Errors that cause the replicator to increase its replication rate (or don�t change it) Which kind of error will be retained? 31

32. Replicators Original replicators, 4 billions years ago. Copying errors are inevitable Replicators came into competition Selection favored: Stability Fecundity � Speed of replication Copying fidelity Power to influence own survival e.g., build a protective coat which increases stability 32

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34. Perfect replication (physics): crystals -- no alternatives (nanotech/vaccine/disk/ digital) no evolution is possible Less than perfect replication means there can be change along lineages (evolution) replication + low mutation = capacity to evolve = life in an interesting sense can accumulate functional design There is a capacity to evolve if�. Fatal disintegration is avoided Difficult to do (e.g., movie Hollow Man) 34

35. Results The evolution of organisms (vehicles) whose phenotypic properties are shaped solely to promote the survival of the genes (replicators) that directed their construction. An organism is a �survival machine� built by genes. Organisms = mortal Genes = potentially immortal 35 But, always keep in mind, genes are DNA molecules, not little conscious entities with beliefs and desires, who want us to reproduce so they can survive. A chicken is just the DNA�s way of making more DNA. THere is an unbroken chain of reproductive events leading from the very first replicators to you here today!But, always keep in mind, genes are DNA molecules, not little conscious entities with beliefs and desires, who want us to reproduce so they can survive. A chicken is just the DNA�s way of making more DNA. THere is an unbroken chain of reproductive events leading from the very first replicators to you here today!

36. Genes as the unit of selection Two BIG Leaps DNA: A particular sort of very successful replicator. Cells: Stuff DNA builds. A vehicle for replicators Note that: Genes (i.e., replicators) live forever (by making copies of themselves). Individuals (i.e., vehicles) die (by dying). This is why genes, not individuals, groups, or species, are best thought of as the unit of selection. 36

37. Focus on Replicator Survival As opposed to reproduction of individual Helps explain: How forms of altruism can evolve: kin selection Conflicts between: siblings, parents and offspring, Mates Between different replicators in the same organism (mDNA versus nuclear genes) 37

38. What is the role of genes? Only genes survive to the next generation � they are true replicators. Your offspring are not exact copies of you, but their genes are exact copies of yours (and your mate�s) Genes survive because they build parts of organisms the right way. 38 Genes build adaptationsGenes build adaptations

39. Goal: To avoid teleological thinking Teleology: Explaining the present in terms of some possible future benefit Belief in or the perception of purposeful development toward an end, as in nature or history. To avoid teleology, good of the species thinking, and other mistakes, need to learn to think causally: The past (not the future) determines the present. Example: Imagine two alleles with different average effects on phenotypes: Which will become more common from one generation to the next? 39

40. For example, What if there was a mutation that caused an individual to sacrifice itself for another (random) member of the group. Would this trait be passed on? What about a mutation that caused a male to not care whether the offspring he raised were his own or not. Would this mutation spread? What about a mutation that caused an individual not to reproduce when the population was getting too large? Would this design spread? These designs would cause their own frequency to decrease. We are not descended from individuals bearing those mutations 40

41. Darwinian fitness is the spreading of genes that are most fit. How can this competitive process of natural selection lead to the evolution of cooperation and restraint? Individuals competed for resources such as food, shelters, and mates, that led to survival and reproduction. It�s a dog eat dog world Initially, it was believed that it could not. So other levels of selection were invoked to explain the existence of seemingly contradictory behaviors such as helping and restraint. 41

42. Group selection is the idea that behaviors evolved that were disadvantageous for the individual but profited the group. This way of thinking was popular for some and was used to explain behaviors and phenomena that seemed contrary to genic or individual selectionist theories. 42

43. Group selection was invoked to explain: Lorenz dominance hierarchies absence of aggression, ritualized aggression Genetic variation in populations sexual reproduction social structure -- society as an organism sacrifice to the group: the �law of the pack� struggles of groups, nations, �races� 43

44. Group selection was invoked to explain: Everything �Adapted� or functional features of individuals, groups, populations, species, even assisting the process of evolution Beneficial features were present because they contributed to the survival of the species: teleology Prince Peter Kropotkin versus Hobbs Kropotkin argued that it was cooperation rather than struggle that accounted for the evolution of man and human intelligence. Wynne-Edwards population control: carrying capacity reproductive restraint -- we will use this as an example. 44

45. Reproductive Restraint Wynne-Edwards, a proponent of group selection, explained reproductive restraint as a mechanism to curb population growth of the species. Evidence: Flickers, were found to be capable of producing many more eggs than they in fact rear. Females of this species tend to produce clutches of 6-8 eggs. Egg removal experiments found that physiologically, females could produce many more. 71 eggs over the course of 72 days! 45

46. Group Selection on trial David Lack an ornithologist demonstrated that this reproductive restraint documented by Wynne-Edwards was not due to group selection. He looked at birds and the number of eggs laid in a given season. The question: Are females holding back and not producing as many eggs as she could rear so that the population doesn�t sky rocket? Or, are females in fact producing as many eggs as they will be able to successfully raise to maturity? 46

47. Lack looked at female swifts who lay about two eggs in a single clutch. Egg removal experiments showed that they can physiologically produce many more eggs But, it is not about quantity per se, but how many you can produce that will survive to reproduce themselves. What might affect the probability of survival and reproduction? 47

48. What factors might affect clutch size? Availability of food sources Health and ability of parent to rear young When clutches of 3 were experimentally increased to 4, fewer fledglings survived to reproduce. Allocating parental effort out of finite parental resources Large litters versus selection for small litters. Maximizes parent�s lifetime reproductive success 48

49. Which design would be selected for? One that tried to do it all at once and risked own health and ability to feed offspring, or one who produced fewer offspring in each clutch but produced multiple clutches over the lifetime? 49

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55. These species of birds must have design features that allow them to calculate the optimum number of eggs to lay in a particular clutch given resource availability, ability to rear young, and probability of offspring surviving. Tests on bird species: swifts found that it isn�t number alone but: number X survival X parental quality Maximization of number of offspring successfully raised to healthy, reproductive maturity Maximization of lifetime reproductive success 55

56. Sorry group selectionists Reproductive restraint in birds was found to be an illusion. Birds are not restricting how many eggs they lay so that the population will stay under control. Instead, they are producing the optimum number of eggs in a given clutch that will survive and reproduce. 56

57. Group selection What is the fate of a mutation that sacrifices its own reproduction for the benefit of the group? Will it become more frequent or less frequent? Natural selection acts not on individuals, populations, or species, but on alternative alleles competing at the same locus in the species So the explanation for an adaptive trait must always be: How is it adaptive in spreading itself compared to other alleles at the same locus? Everything else is a side effect. 57

58. Genic selection: The case of inclusive fitness 58

59. Definition of altruism A design feature (gene) that causes its bearer to behave in ways that: increases another individual�s chances of surviving and reproducing i.e., their fitness and decreases their own fitness Causes is in a statistical sense. Observations of genuine altruism: sterile individuals among social insects alarm calls Causes is in a statistical sense. Observations of genuine altruism: sterile individuals among social insects alarm calls

60. The problem of altruism Natural selection ? differential reproduction A design that helps others is costly. Consider the fate of a mutation that helped others versus one that was selfish How in the world can a gene that causes its bearer to suffer a reduced probability of survival and reproduction evolve??????????? Doesn�t this mean that selection can never favor altruism? How can niceness (altruism) evolve?

61. Let�s start with a population of� Indiscriminate Altruists Doesn�t care about who receives their help Doesn�t care if the favor is ever returned Doesn�t care about the cost of help Everybody has the gene to help others whenever, where ever, etc.

62. Imagine a mutation� Causes an individual to receive help but never give it! Not incurring same costs Only benefiting Which behavior will win out? What would happen?

65. Question: If not indiscriminate altruism, what are the conditions under which caring for another�s welfare can evolve?

66. We�re talking about the selection of genes that produce helping behavior. How can a particular gene that causes helping behavior spread? If you help individuals at random, this cannot change the frequency of any allele time they share the same allele canceled by the times they do not.

67. What if there was a mutation that caused someone to help another individual who happened to have the same gene? How would you know they had the same gene? What if there was a marking like a green beard. What if you knew who shared the same gene (and behavior)?

68. Green Beards So let�s say a gene has two effects: produces a greenish beard motivates helping toward those who have a green beard.

71. Evolution of altruism is not straight forward. Is there someway to know who has a probability of sharing a particular gene in common? Who has a high probability of sharing a particular gene? The lesson of indiscriminate altruists and green beards

72. Have to think about the different ways a gene can spread. How can a gene increase in frequency? Answer: It can make copies of itself It can help make copies of copies of itself Intentional language warning!

73. YOUR FAMILY:CLOSE GENETIC RELATIVES

74. Kin Selection/Inclusive Fitness Theory W.D. Hamilton (1964) An allele may spread because it causes its bearer to reproduce (RS), OR� because it causes its bearer to help others to reproduce who are likely to carry the same gene. This is called kin selection because individuals who are likely to carry the same genes are genetic relatives. have the same genes from having ancestors in common.

75. Kin Selection Theory: A major scientific advancement Major theoretical reconceptualization of the nature of living things Old view: All organisms are selected to be completely selfish Nature red in tooth and claw Hobbesian war of all against all Nonselfishness result of effortful socialization against intrinsic selfish tendencies

76. New view: Altruism and convergences of interest as intrinsic to the design of organisms as is selfishness and conflicts of interest. In the early 1960�s, biologists (John Maynard Smith, George Williams, and especially W.D. Hamilton) recognized that because relatives sharing traits or genes could also pass them on, designs could be selected for which traded off their own reproductive success to enhance the reproduction of their relatives.

77. Fitness and Inclusive Fitness Fitness: The ability for a design feature to reproduce itself by promoting the survival and reproduction of its bearer Inclusive fitness: The ability of a gene (design feature) to cause its own spread either through its bearer or those having a high probability of sharing the gene, close genetic relatives.

78. But, don�t we all share genes? By virtue of being members of the same species, we all share approximately 99% of the same genes. However, the variation in the other 1% of the genome allows for the evolution of kin selection.

79. Degree of relatedness (r) r is the probability an allele present in one individual is present in another individual, over and above the population average frequency of the allele. r is the probability that alleles sampled from 2 individuals are identical by descent Events of mating organize relatedness between individuals.

80. Degree of relatedness (r) r =0.5 for: Parents & offspring Siblings r=0.25 between: Grandparents & grandchildren Uncles or aunts & nieces or nephews Half siblings r=0.125 between: 1st cousins r=0 between: Step parents & children Step siblings

82. Asexually reproduced individuals, and identical twins, are genetically identical. Therefore, r=1.0

83. What is the probability you share a gene with your sister? Consider each possible route of transmission separately Mom Probability a gene in you came from mom: Probability mom gave sib same gene: Total probability share through mom? Dad Probability a gene in you came from dad: Probability dad gave sib same gene: Total probability share through dad? Combined probability of sharing same gene?

84. Eusocial insects Unfertilized eggs develop into males. Fertilized eggs develop into females. What is r between sisters? Mom Probability gene in sis1 came from mom Probability mom gave sis 2 same gene Total prob gene came from mom Dad Prob gene in sis1 came from dad Prob dad gave sis 2 same gene Total prob gene came from dad r

85. Hamilton�s Rule When should you help someone? When the B to them > C to you But need to take into account probability of sharing the same gene (allele) for helping Whether you help someone is a function of: The probability you share the same gene (r) How costly it would be to help (C) How much of a benefit the person receives (B) Hamilton�s rule: rB>C In general, the more related, the greater the helping behavior.

86. rB>C Should you help your sibling? B = 10, C=6, r = � rB>C? (1/2)10 > 6? 5 > 6? No! Does not pay to help in this situation Should you help your sibling? B = 8, C = 3, r = � rB>C? (1/2)8 > 3? 4 > 3? Yes! So it pays to help What if it was an uncle or aunt? (r=1/4)

87. An ESS is a behavior/strategy/trait that is the optimal solution and cannot be replaced or out-competed by mutants. Hamilton�s rule (C<rB) is an evolutionary stable strategy: Individual�s who had psychological adaptations that generated behavior according to Hamilton�s rule tended, on average, to leave a greater number of offspring. No other strategy would out-compete this rule Aliens Evolutionary Stable Strategy

88. Hamilton�s Rule: What it does and doesn�t mean. This rule is about selection pressures. It indicates what mechanisms can be selected for Does NOT indicate organisms will come to be designed to consciously �try� to �help� Again, people don�t have the �goal� of promoting replication of their genes � they might have mechanisms that were selected because of Hamilton�s rule.

89. ESS Can also talk about sexual strategies For example: In a population of males who spend time and energy investing in offspring, would it pay for a male to adopt a short-term mating strategy? Sneak fertilizers Male infanticide in langurs which strategy would do better?

90. Killing the nature/nurture dichotomy until it is dead. Misunderstandings to avoid 90

91. BIOLOGICAL IS NOT THE OPPOSITE OF LEARNED Question: Are calluses biological or cultural? Answer: neither. More bad questions: �Is aggression due to nature or nurture?� �Which is more important in aggression, nature or nurture?� �What makes a car go, the engine or the gasoline� Similar bad dichotomies: biological/cultural, innate/learned, gene/environment. 91

92. The issue that gets confused with nature/nurture: heritability KEEP THESE TWO QUESTIONS SEPARATE: What is the universal human evolved architecture? (Variability comes from adaptive responding to environment.) Given a large population of people, to what extent can differences between these people be accounted for by differences in their genes? (heritability) 92

93. Phony issue: genes vs. environment Heritability statistic (h) h = Vg/(Vg+Ve+Vge) Vg = variance due to genes Ve = variance due to environment Vge = variance due to the interaction of both genes and environment Applied to populations, not individuals � an individual does not have variance! 93

94. Heritability Something that has no genetic variance has a heritability = 0 Doesn�t mean trait isn�t inherited Two legs, heart, brain, etc Heritability doesn�t tell you how difficult it is to change a particular behavior. When measuring heritability, important to know what environment you are measuring it in. 94

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96. Heritability You can�t talk about the heritability of a certain trait without knowing what kind of environment you are measuring it in. The genetic variation doesn�t express itself in the environmental conditions it evolved in � only in novel environments. 96

97. More �nature� = More �nurture� A vehicle with a sensor attached to a motor. 97

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99. Misunderstandings to be strenuously avoided� Genetic Determinism Individual Differences Inalterability Innateness at birth Optimal design Do people try to replicate their genes? Improbable computational abilities 99

100. Genetic Determinism Wrong: to say something is evolved is to say only genes matter. Right: Biological approaches emphasize environmental inputs � phenotypes are ALL the joint product of genes and environment Development is complex A goal is to specify what environmental inputs are relevant for different traits/phenotypes 100

101. Individual differences Wrong: To say that something is evolved is to say that there is no individual variation in it. Right. Genes are selected to construct adaptations, but the construction process is complex, and the target is not always hit perfectly. Example: eyesight. Also, many adaptations develop contingent on the environment (what language you speak, calluses�) 101

102. Inalterability Wrong: �Genetic� implies �fixed� Right: Adaptations are designed to respond to environmental elements Examples: calluses, pku 102

103. Innateness at birth Wrong: To say that something is evolved is to say that it is present at birth. Right: Many adaptations take time to appear. Examples: teeth, breasts 103

104. Optimal design Wrong: Adaptationists think that all aspects of organisms are perfectly designed and functional Right: Many reasons for sub-optimal designs: Local maxima in a fitness landscape. Time lags, novel environments. Many parts of organisms are by-products of adaptations Constraints you haven�t figured out: �Evolution is smarter than you are.� � Leslie Orgel 104

105. Do people try to replicate their genes? Wrong: Peoples� motivations are identical to the laws of natural selection. For example, all people want is to have sex and not die. Right: Natural selection designs motivational systems that are specialized for specific tasks. That is, genes build systems that function such that they led to their own replication. There are many cases where these produce behavior that does not promote reproduction or survival. For example, we are fond of fat and sugar even when it is �bad� for us. 105

106. Fallacy of attributing evolutionary purposes to species, individuals, or genes Each only carries out whatever causal rules are built into it they do not seek evolutionary goals, like survival -- no imperative to survive Wrong idea: organisms develop group-beneficial traits (or species-beneficial traits) because those that don�t become extinct Animals don�t reproduce to insure the survival of the species 106

107. They reproduce because they inherited machinery that caused them to do things which usually led to reproduction They inherited the genes to build such machinery because such genes caused themselves to spread in the species Species survival, when it occurs, is a byproduct of the fact that individual reproduction usually increases species reproduction 107

108. Improbable computational abilities WRONG: Hunters and gatherers do not have counting systems beyond one, two, and three. I refrain from comment on the even greater problem of how animals are supposed to figure that r [genetic relationship between the animal and its first cousin] = 1/8. The failure of [people like me] to address this problem introduces considerable mysticism in their theory. --Sahlins, 1977, 444-445 Right: Conscious awareness of computations are unnecessary for performing a task. Do spiders �understand� the physics of web-spinning? 108

109. Finally: The Naturalistic Fallacy WRONG: To say that something is evolved is to say that it is good, and ought be that way. Right: Science is a process of trying figure out what is true. Morality is not something that is in the world to be discovered. Biological scientific approaches are just that, scientific approaches. 109