Evolutionary Psychology. Honors Psychology Dr. John Opfer

Transcription

1 Evolutionary Psychology Honors Psychology Dr. John Opfer

2 Natural Selection & Psychology Previously, we saw how genes constrain behaviors Now, we will see how natural selection constrains gene distribution Thus, we can see how natural selection constrains the distribution of behavior In this way, natural selection will allow us to predict and explain behavior

3 Thought experiment: Biologists recently discovered a population of plants (hausitoria) with very long pulegone. How would biologists explain how a population of hausitoria with long pulegone evolved from an ancestral population with short pulegone?

4 Natural Selection of Behavior Evolution by natural selection rests on three principles that interrelate genes and behaviors 1. The principle of variation: Within a population, individuals vary in behavior. 2. The principle of heredity: Offspring resemble their parents in behavior more than they resemble unrelated individuals. 3. The principle of selection: In a given environment, some heritable behaviors benefit the individual s survival and reproductive success more than other heritable behaviors. Therefore, these heritable behaviors will predominate in that environment from generation to generation.

5 Artificial Selection Breeder s Equation: R = S x h 2

6 Artificial Selection Plants Breeder s Equation: R = S x h 2

7 Artificial Selection Learning Breeder s Equation: R = S x h 2

8 Artificial Selection Social Behavior

9 Artificial Selection Correlated Variation Hairless dogs have imperfect teeth; long-haired and coarse-haired animals are apt to have, as is asserted, long or many horns; pigeons with feathered feet have skin between their outer toes; pigeons with short beaks have small feet, and those with long beaks large feet. Hence if man goes on selecting, and thus augmenting, any peculiarity, he will almost certainly modify unintentionally other parts of the structure, owing to the mysterious laws of correlation. Charles Darwin, On the Origin of Species

10 Artificial Selection Darwin observed that specieslike variation arises under domesticated species For example, a population of fruit flies will vary in the number of abdominal bristles. Experimenters can then select many- or few-bristled flies to reproduce. After 35 generations, the phenotypic distributions of the groups will differ substantially as a result of differential selection of their naturally varying genotype.

11 Natural Selection West African finches face a similar selection differential to the artificial one experimenters placed on the fruit flies. In this finch s environment, seeds tend to be either very soft or very hard, which requires either narrow or hard bottom bills. Intermediate sized bills are not adaptive in this environment, so the variation in bottom bill size is centered around the size that is most adaptive for cracking either hard or soft seeds.

12 Evolution of Beaks: Darwin s Finches The Blue-black grassquit of the Galapagos Islands. Some islands mountainous and rainy, some flat and arid Islands are so far apart that few finches ever migrate to another island. As a result, 14 different species of the finch have evolved.

13 But what does this have to do with PSYCHOLOGY?????

14 Bird Species Brain Power Clark's nutcracker Pinyon Jay Scrub Jay Reliance on Stored Food Lives high in mountains; stores food in summer and relies on finding it to survive the winter Lives at fairly high altitude; depends partly on stored food to survive the winter Stores some food but less dependent on it Size of Hippocampus Relative to Rest of Brain Largest Second largest Smaller Performance on Lab Tests of Spatial Memory Best Second best Less good Mexican Jay Stores some food but less dependent on it Smaller Less good From Kalat, 1998; based on results of Basil et al., 1996, and Olson et al., 1995.

15 Species Clark's nutcracker Pinyon Jay Scrub Jay Reliance on Stored Food Lives high in mountains; stores food in summer and relies on finding it to survive the winter Lives at fairly high altitude; depends partly on stored food to survive the winter Stores some food but less dependent on it Size of Hippocampus Relative to Rest of Brain Performance on Lab Tests of Spatial Memory Performance on Lab Tests of Color Memory Largest Best Slightly worse What should you predict about their mental abilities? Second largest Second best Slightly better Smaller Less good Slightly worse Mexican Jay Stores some food but less dependent on it Smaller Less good Slightly better From Kalat, 1998; based on results of Basil et al., 1996, and Olson et al., 1995.

16 Species Clark's nutcracker Pinyon Jay Scrub Jay Reliance on Stored Food Lives high in mountains; stores food in summer and relies on finding it to survive the winter Lives at fairly high altitude; depends partly on stored food to survive the winter Stores some food but less dependent on it Size of Hippocampus Relative to Rest of Brain Performance on Lab Tests of Spatial Memory Performance on Lab Tests of Color Memory Largest Best Slightly worse Second largest Second best Slightly better Smaller Less good Slightly worse What should you predict about their brains? Mexican Jay Stores some food but less dependent on it Smaller Less good Slightly better From Kalat, 1998; based on results of Basil et al., 1996, and Olson et al., 1995.

17 Evolution of Mental Capacities: North American Jays Species Clark's nutcracker Pinyon Jay Scrub Jay Reliance on Stored Food Lives high in mountains; stores food in summer and relies on finding it to survive the winter Lives at fairly high altitude; depends partly on stored food to survive the winter Stores some food but less dependent on it Size of Hippocampus Relative to Rest of Brain Performance on Lab Tests of Spatial Memory Performance on Lab Tests of Color Memory Largest Best Slightly worse Second largest Second best Slightly better Smaller Less good Slightly worse Other explanations? Mexican Jay Stores some food but less dependent on it Smaller Less good Slightly better From Kalat, 1998; based on results of Basil et al., 1996, and Olson et al., 1995.

18 Evolution of Mental Capacities: North American Jays Species Clark's nutcracker Pinyon Jay Scrub Jay Reliance on Stored Food Lives high in mountains; stores food in summer and relies on finding it to survive the winter Lives at fairly high altitude; depends partly on stored food to survive the winter Stores some food but less dependent on it Size of Hippocampus Relative to Rest of Brain Performance on Lab Tests of Spatial Memory Performance on Lab Tests of Color Memory Largest Best Slightly worse Second largest Second best Slightly better Smaller Less good Slightly worse Mexican Jay Stores some food but less dependent on it Smaller Less good Slightly better From Kalat, 1998; based on results of Basil et al., 1996, and Olson et al., 1995.

19 Species Clark's nutcracker Pinyon Jay Scrub Jay Mexican Jay Reliance on Stored Food Lives high in mountains; stores food in summer and relies on finding it to survive the winter Lives at fairly high altitude; depends partly on stored food to survive the winter Stores some food but less dependent on it Stores some food but less dependent on it Size of Hippocampus Relative to Rest of Brain Performance on Lab Tests of Spatial Memory Performance on Lab Tests of Color Memory Largest Best Slightly worse What what do bird Second largest Second best Slightly better brains and beak sizes Smaller Less good Slightly worse tell us about psychology? Smaller Less good Slightly better From Kalat, 1998; based on results of Basil et al., 1996, and Olson et al., 1995.

20 Natural Selection & Behavior Natural selection offers explanations for three types of phenomena Species-Typical behaviors (e.g., why all canaries sing the canary song) Species-Differences in behavior (e.g., why the songs of canaries and finches differ) Species-Similarities in behavior(e.g., why canaries and finches sing)

21 Adaptationist Explanations of Species-Typical Behaviors 1. Species often face the same problems For example, finding mates of the same species is a problem all sexually reproducing organisms face. 2. Behaviors that solve these problems will become species-typical if they are heritable For example, bird songs if adaptive and heritable might be species-typical. 3. Thus, species-typical behaviors warrant adaptationist hypotheses For example, if bird songs are species-typical, then we could say that they are good for whatever their adaptive value is, such as finding mates of the same species

22 Testing Adaptationist Explanations To test adaptationist explanations, deprive species of their ability to behave in a species-typical manner, or simulate natural behavior and observe the effects. Following the second strategy, Yasukawa (1981) found that Recordings made of one species of bird song are likely to attract females of that species, repel males of that species, and have no effect on other species of birds Thus, one function of species-specific bird song is for males to find mates of the same species while warding off competitors.

23 Two Types of Adaptations: Instincts vs. Instincts to Learn Are the mechanisms that produce the bird song already in the chick s brain and triggered by the environment, or is it not yet in the brain but acquired by biologically-prepared, species-typical learning?

24 Two Types of Adaptations: Mature vs. Developmental Mature adaptations meet organisms biological needs in adulthood For example, the mechanisms that produce bird songs may already be present in the brain, and simply triggered by the environment so that the adult can find mates Developmental adaptations meet organisms need to attain adult behaviors. For example, the mechanisms that produce bird songs may develop within the lifetime of the organism. That is, bird songs are learned. This learning may be biologically prepared so that adults can find mates.

25 Mature Adaptations: The Example of Fixed Action Patterns Fixed action patterns are mature adaptations, fixed in the animal s nervous system, relatively unmodifiable by learning, and triggered by a sign stimulus. The aggressive behavior of the male stickleback is species-typical. The sign stimulus is a red-belly, which is characteristic of breeding male sticklebacks that threaten other male stickleback s reproductive success. Where the behavior is useless (outside the stickleback s nest), the sign stimulus elicits no behavior.

26 Developmental Adaptations: The Example of Biologically-Prepared Learning Biologically-prepared learning processes are developmental adaptations in that they prepare the organism to attain behaviors by adulthood that are adaptive for adults. Example: White-crowned sparrows have a species-typical song They only learn to sing this song if they are permitted to hear it during their first summer after hatching During this time, they will learn to sing whatever song adult white-crowned sparrows sing But they can never learn to sing the songs of other species, such as canaries. Aspects of human language also show this critical period of acquisition

27 Critical Periods in Humans Language Newport (1990)examined the grammaticality of immigrants speech all had been in US for over 40 years

28 Inferring Lineage from Species-Similarities Tracing the evolutionary lineage of species-typical behaviors is difficult because we have to infer lineage by looking at similarities across living species, which are simply cousins. Two types of similarities: Analogies are similarities that result from mechanisms that evolved independently to meet similar needs. They arise from shared functions, which result only in similar gross similarities of form even when the underlying construction is different. Examples: similar wings among insects, flying fish, birds, and bats; living in groups in birds and humans Homologies are similarities that result from mechanisms that were evolutionarily conserved (inherited) from a common ancestor. They arise from shared genes, which result in shared physiological constructions even when gross forms are different. Examples: similar wings among species of finches, hive-building in various bee species

29 An Evolutionary Homology: Human Emotional Expressions Cultural anthropologists such as Margaret Mead long claimed that facial expressions bear no necessary relation to emotions, but are determined by one s culture. Psychologists such as Paul Ekman have tested this model against Darwin s model that emotional expressions have been evolutionarily conserved. Ekman and others have found that emotional expressions are: Culturally universal: People from every continent, including those who have virtually no contact with outsiders, manifest many emotions in exactly the same way Unlearned: Blind and deaf children manifest many emotions exactly as sighted children do Primate-typical: Orangutans, gorillas, chimps, and humans all express fear, surprise, anger, happiness, and sadness using exactly the same face muscles.

30 An Evolutionary Analogy: Evolution of Sex Differences Related species that show similar patterns of parental investment show similar sex-differences Polygyny: Polygyny arises where maternal investment is needed more than paternal investment Polygyny creates male-male competition (& big, vicious males) Seen in elephant seals and some European blackbirds Polygynandry: Polygynandry rises when parental investment is needed from the entire colony Paternity confusion maximizes parental investment and creates sperm-competition Seen in closely-related chimps and bonobos

31 Human Mate Selection One of the most controversial set of predictions made by evolutionary psychology concerns sex-differences in human mate selection. Are our preferences in potential sexual partners shaped by natural selection?

32 Human Mate Selection A Thought Experiment: Design two aliens (sex alpha, sex beta) that will successfully reproduce with the natives and spread their genes as widely as possible over the generations If genes could code mate selection strategies, which ones would be maximally efficient at getting copies of themselves spread throughout a population? It depends... 1) Minimum Parental Investment 2) Time Horizon

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38 Designing Successful Reproduction Machines Minimum Parental Investment Common gametes (e.g., lots of sperm/day + zero gestation) Rare gametes (e.g., one egg/ month + long gestation) Time Horizon Long-term Short-term

39 Designing Successful Reproduction Machines When minimum parental investment is high, It becomes a limiting resource, leading to greater competition Cost of wrong decision is very high, leading to greater selectivity

40 Designing Successful Reproduction Machines Minimum Parental Investment Common gametes (e.g., lots of sperm/day + zero gestation) Rare gametes (e.g., one egg/ month + long gestation) Time Horizon Long-term Outcompete other alphas for fertile betas Be choosy; get genes + added value Short-term Outcompete other alphas for fertile betas Be choosy; get best possible genes

41 Designing Successful Reproduction Machines When time horizon is short, find mate that will contribute genes that enhance inclusive fitness of offspring When time horizon is long, find mate that will add value to genetic contribution

42 Designing Successful Reproduction Machines Minimum Parental Investment Common gametes (e.g., lots of sperm/day + zero gestation) Rare gametes (e.g., one egg/ month + long gestation) Time Horizon Long-term Outcompete other alphas for fertile betas Be choosy: look for good dads Short-term Outcompete other alphas for fertile betas Be choosy: look for good genes

43 Predictions about Human Mate Selection According to Buss (1994), there should be two sets of strategies humans use strategies for short-term and long-term relationships, which are derived from differences in minimum parental investment. For males, short-term and long-term strategies should be very similar because their minimal parental investment is low. Therefore, they should look for signs of fertility in prospective partners youth, a pelvis adapted for child-birth, no signs of disease, etc. For females, short-term and long-term strategies should be very different because their minimal parental investment is high. For short-term relationships, they should look for signs of good genes health, height, strength, etc. For long-term relationships, they should look for signs of potential for male parental investment social status, financial health, kindness and warmth, humor and intelligence.

44 International Study of Mate Preferences Buss, samples of people 10,047 subjects drawn from 33 countries located on 6 continents rated 18 characteristics on a 4-point scale ranging from 0 = irrelevant 3 = indispensable

45 Locations of 37 Cultures in IMSP

46 Preferences that are relatively similar among men and women: Mutual attraction-love Exciting personality Healthy Pleasing disposition Kindness & understanding Education & Intelligence Sociable Refinement-Neatness Wants children Easy going Creative & artistic

47 Sex Differences in Preferences

48 1. Preference for potential resources

49 2. Preference for potential resources

50 3. Preference for youth* Data from dating website OKCupid!

51 3. Preference for youth* Data from cross-cultural studies

52 Actual Age Differences in 1,511 Marriages on the Island of Poro ( )

53 4. Interest in Infants

54 5. Desire for physical attractiveness in long-term mate

55 Fertility or Reproductive Value Cues Full lips Clear skin Clear eyes Lustrous hair Muscle tone Sprightly gait Symmetry Health Youth Etc. Standards of Attractiveness

56 Body shape (WHR)--fertility cue

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58 A Pattern Emerging Men look for potential to bear children: Don t put premium on resources Seek women of fertile ages (not younger than puberty, not much older than peak fertility) Women look for potential to invest in children: Seek resources (or potential resources) Seek men slightly older (i.e., with more resources)

59 Human Mate Selection Knowns: Evolutionary predictions about sex differences in mate selection strategies have received wide support from studies performed all over the world. Unknowns: Heritability of mate selection strategies are unknown Unlike the selection of hippocampal size among species of North American Jays, no brain mechanism to date has ever been found to account for sex differences in mate selection strategies.