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Chapter 8

CHAPTER 8 NOTES - Evolutionary Psych

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PSYC 3420
Irwin Silverman

CHAPTER 8: PROBLEMS OF KINSHIP THEORYAND IMPLICATIONS OF INCLUSIVE FITNESS •Favouritism that parents show their own children can be viewed as a special case of favouritism toward the "vehicles" that contain copies of their genes HAMILTON'S RULE •Altruism is defined by two conditions: 1. Incurring a cost to the self 2. To provide a benefit to the other person •Hamilton's insight: altruism could evolve if the costs to the self were outweighed by the benefit to the recipient of the altruism, multiplied by the probability that the recipient carried a copy of that gene for altruism •Hamilton's rule: natural selection favours mechanisms for altruism when c < rb 1. c= cost to the actor 2. r= the degree of genetic relatedness between actor & recipient 3. b= benefit to the recipient •Selection will favour an individual to incur costs (being 'altruistic') if the benefits to a .50 kin member are more than 2 times the costs to the actor; if the benefits to a .25 kin member are 4 times the costs to the actor; or if the benefits to a .125 kin member are more than 8 times the costs to the actor •Ex. You would jump in a river to save your genetic relatives; selection will favour decision rules if you're going to save three of your brothers, but not one 1. You wouldn’t sacrifice your own life for one brother (because otherwise that would violate Hamilton's law) •Evolvability constraint: only genes that code for traits that fulfill Hamilton's rule can spread throughout the population and hence evolve to become part of the species-typical repertoire THEORETICAL IMPLICATIONS OF HAMILTON'S RULE •The most important implication of Hamilton's theory of inclusive fitness is that psychological adaptations are expected to have evolved for different types of kin relationship Sibships: •Brothers and sisters impose unique adaptive problems and have done so recurrently throughout human evolutionary history •They can be a major social ally (they're related to you by 50%) •They can also be a major competitor for parental resources •Sulloway's theory of birth order: It's been proposed that the adaptive problems imposed by parents on children will create different "niches" for children, depending on their birth order o Since parents favour the first born, he/she is more likely to be more conservative and more likely to support the status quo • First borns receive all the parental investment EVOLUTION CHAPTER 8 page 1 o Second borns have little to gain by supporting the existing structure and everything to gain by rebelling against it o Later borns, specially middle borns, develop a more rebellious personality because they have the least to gain by maintaining the existing order • Middle borns receive less total parental investment o The youngest might receive more parental investment than middle children, as parents often let out all the stops to invest in their final direct reproductive "vehicles" • Salmon and Daly have found some support for these predictions Sibs vs. Half Sibs: • Full sibs genetically related by 50%, half sibs are genetically related by 25% • Ex. In squirrels, Warren Homes and Paul Sherman discovered that full sisters were far more likely than half-sisters to cooperate in the mutual defense of their young Grandparents and Grandchildren: • Grandparents are related to their grandchildren by 25% • Grandmother hypothesis: the fact that modern women often live well beyond menopause has led to the hypothesis that menopause itself evolved as a means of ceasing direct reproduction to invest in children and then grandchildren Hypothesis about universal aspects of kinship: • Daly, Salmon, and Wilson outline a set of hypotheses about the universal aspects of the psychology of kinship Implications of Inclusive Fitness Theory: 1. There will be a special evolved psychology of kinship involving psychological mechanisms dedicated to solving the differing adaptive problems confronted when dealing with siblings, half siblings, grandparents, grandchildren, aunts, and uncles 2. Sex and generation will be critical categories differentiating kin because these dimensions define important properties on one's fitness vehicles 3. Kin relationships will be arrayed on a dimension from close to distant, the primary predictor of closeness being genetically related 4. Cooperating and kin solidarity will be a function of genetic relatedness among kin 5. Older kin members will encourage younger kin members to be more altruistic toward genetic relatives such as siblings than younger kin members will naturally be inclined to be 6. One's position within the family will be central to one's identity 7. People will exploit kin terms to influence and manipulate others in non-kin contexts 8. People everywhere will be aware who their "real" relatives are 9. Kinship terms will be used to persuade and influence other people, even when no kinship is involved ALARM CALLING IN GROUND SQUIRRELS • When Belding's ground squirrels detect a predator, such as badger or coyote, they sometimes emit a high-pitched staccato that functions as an alarm call alerting other ground squirrels in the immediate vicinity to danger Three hypotheses that explain the apparent act of altruism: EVOLUTION CHAPTER 8 page 2 1. Predator confusion hypothesis: the alarm call might function to confuse the predator, in which all squirrels rush around for safety 2. Parental investment hypothesis: although the alarm caller is at greater risk by sounding the signal, his/her children are more likely to survive 3. Inclusive fitness hypothesis: the signal alerts the "vehicles" that contain copies of the squirrel's genes, providing an inclusive fitness benefit •Sherman tested out the first hypothesis, and found that the predators are NOT confused by the alarm call, instead they home on the alarm caller directly •Since females give off more alarms than males do, it supports both hypothesis 2 and 3 •Even female squirrels that don’t have genetic relatives still do the alarm calling KIN RECOGNITION AND KIN CLASSIFICATION IN HUMANS Kin Recognition mechanisms: 1. Association: Researchers believe that early association - exposure to kin in infancy - is the key cue that primates use o Association during childhood in human populations is known to produce subsequent sexual aversion, functioning as incent avoidance adaptation 2. Odor: We can detect kin by smell 3. Kin Classification System based on a Universal Grammar: We can identify kin through kin terminology o The grammar consists of 3 innate primitives of social cognition: • Genealogical distance: how close or distant the kin are • Social rank: relative age; older ranked higher than younger • Group membership: different clumps of kin 4. Phenotypic resemblance: similarity between your face or body and the faces or bodies of others •Humans can detect kinship among strangers or groups of other people to whom they are not related •The upper part of the face seems to be especially important for kinship cues •When the lower part of the face was masked = performance on kin recognition decreased by 5% • When the upper part of the face was masked = performance on kin recognition decreased by 65% PATTERNS OF HELPING IN THE LIVES OF L.A WOMEN •A study of 300 Los Angeles women found that helping was a function of the genetic relatedness to the individual being helped o Among kin, helping will increase as a function of genetic relatedness o Among kin, helping will increase as the recipient's reproductive value increases LIFE-OR-DEATH HELING AMONG HUMANS •A study by Burnstein, showed that in a hypothetical life-or-death scenarios, such as risking one's life to pull only one person out of the three people from a burning building, EVOLUTION CHAPTER 8 page 3 helping was highly predictable from the degree of genetic relatedness between the helper and the person being helped • Helping in the life-or-death situation decreased as the degree of genetic relatedness decreased • Helping in the life-or-death situation also declined as the potential recipient's age increased GENETIC RELATEDNESS & EMOTIONAL CLOSENESS: IS BLOOD THICKER THAN WATER? • Two theorists have proposed that "emotional closeness" is a psychological mediator • Genetic relatedness predicted willingness to act altruistically o Not only were individuals more likely to be close to their family members who were the most genetically related to them, but emotional closeness also statistically mediated the tendency to behave altruistically toward their family members • Two other indications of emotional closeness: frequency of contact and doing favors • Another indication is the amount psychological grief various relatives experience when a child dies VIGILANCE OVER KIN'S ROMANTIC RELATIONSHIPS • Faulkner and Schaller's study tested two hypotheses: 1. Individuals will maintain greater vigilance over the mating relationships of their close than distant kin 2. Individuals will maintain greater vigilance over the mating of their female than male kin KINSHIP AND STRESS • Stressful situations cause the release of the hormone cortisol into the blood stream • Cortisol's functions: o Releasing energy for action o Affecting mental activity such as degree of alertness • Cortisol tends to inhibit growth and hinder reproductive function • Study by Flinn: growing up without close kin, or in stepfamilies with half siblings, can be stressful, indicated by higher cortisol levels of children in these families in the Caribbean village KINSHIP AND SURVIVAL • Evidence that having kin in close proximity affects actual survival rates during real life-or- death
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