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  1. Family & Friends By Selina Wood and Kathleen Kiang By Selina Wood and Kathleen Kiang

  2. Altruism: Behavior characterized by self-denial or self-sacrifice to benefit others, seen especially among close kin. • Inclusive Fitness: An individual’s own fitness and his/her effect on the fitness of any biological kin. ALTRUISM

  3. Let’s take a closer look at… Inclusive Fitness • Burnstein et al., (1994) pointed out that during natural disasters people's uppermost concern is with their families. • The idea that CONCERN FOR OTHERS should be dependent upon RELATEDNESS has been predicted by evolutionary biologists in their discussions of 'inclusive fitness’. • Our decisions to help/assist another individual should be influenced by the perceived degree of relatedness we share with an individual.

  4. The AGE of both the giver & recipient help determine whether altruism will tend to raise inclusive fitness. • “We regret a young man’s death more than an older man’s.” • Parental devotion should grow until about early adolescence, when reproductive potential peaks. • “Growing intimacy with a person over time and the shrinking size of that person’s unlived life happen to reach some sort of maximum combined grief value right around adolescence.”

  5. Hamilton’s Theory • Genes for sacrificial behavior will thrive as long as the cost to the altruist (in terms of impact on future reproductive success) is less than the benefit to the recipient times the degree of relatedness between the two. • C< BR Kin Selection • Monozygotic (identical) twins would, thus, be expected to show GREATER within-pair altruism than dizygotic (fraternal) twins. • Segal & Hershberger Experiment (1999) : • Compared MZ and DZ twins’ behaviors during a Prisoner’s Dilemma game. MZ twins • made more cooperative choices than • DZ twins, as expected. Looking at Survival from Gene’s Point of View Prisoner’s Dilemma: If one implicates the other, he may go free while the other receives a life in prison. If neither implicates the other, both are given moderate sentences, and if both implicate the other, the sentences for both are severe.

  6. For rich, high-status families, the sons can use wealth and status to produce scores of offspring. • Since girls “marry up” on the socioeconomic scale, mothers in poor physical condition might profit genetically from treating daughters as more valuable assets than sons. • High-status parents spend more time with sons and low-status parents with daughters. • Parents will care relatively little for children who are so defective as to have negligible reproductive value. “MOM & Dad Always Liked You Best”

  7. Relationship rewards: • What kind of threat does the relationship my mom/dad and RIVAL (in this case, a sibling) have pose to the things you get from the relationship? • Hart Experiment • Subjects: 6 month olds (no siblings) • Independent Variable (IV) : • - Mom plays with DOLL(treat it like a sibling) vs. NONSOCIAL TOY (book that makes sounds). • - Nonsocial toy is the control. • Dependent Variable (DV) : • Facial Expressions and Behavior • Results: • - Infants show MORE NEGATIVE AFFECT when mom is interacting with baby doll. • Negative Affect: Doll > Toy • - Even in infants as young as 6 months, jealousy occurs. SIBLING RIVALRY

  8. RECIPROCAL ALTRUISM • The more desperate the plight of the beneficiary, the larger the IOU. • We don’t seem to mind not giving nearly as much as we mind being seen not giving. • With reciprocal altruism the goal is that the organism be left under the impression that we’ve helped; the impression alone is enough to bring the reciprocation.

  9. Ultimatum Game: • Two people come in assigned to either be Proposer and Responder). • Proposer divides the money. Decides how much to keep or give away.. • Responder either accepts or rejects. If he/she rejects, both don’t get anything. • Acceptance  Proposed division occurs. • Rejection  No one gets any money. • U.S Results: • Modal (most often proposed) offer = 50% of $$ • Lowball offers (less than or equal to 30% of $$) often rejected 50% of time. • Suggests that if you were to give only 1/3 of the $$, the other person will say No 50% of the time. • Cameron (1999) • Indonesians played for 200,000 rupees (~ 3 months salary). • Modal Offer: 50% of $$ People generally offer an even split. • Lowball Offer: Rejected 10% of time. • Willing to not get 3 months of salary. • Shows a cultural difference. • Dictator Game • Rules: • “Whatever I say goes.” • Results: • Offers are less equal than Ultimatum Game. • But rarely offer nothing!! Even though there’s no penalty to take all the money, people still gave the other person something. • So.. why not betray your partner entirely? Ultimatum Game

  10. Family Kin Selection Choosing (through natural selection) to forgo reproducing in hopes of increasing a family members reproductive fitness. Thus increasing inclusive fitness. Natural selection working on the gene not the individual or family. Hamilton’s Theory Idea that one is more likely to be altruistic towards family verses strangers to increase reproductive fitness. Sibling Paradox No such thing as unlimited love Help a sibling but also compete for resources between mum and dad.

  11. Mothers and Others Sarah Hrdy Alloparenting Humans Callitrichids No other primates Allows for ‘stacking’ babies Greater Parental involvement/ familial involvement May have developed due to mind reading Grandmother Hypothesis Humans have a longer life span due to grandmother care needed as a maternal resource.

  12. Genetic relatedness and sibling relationshipcharacteristics in a modern society • Studies contemporary ‘patchwork families’ and relationships between siblings (half, step, full) • Studies show more conflict in a household with half siblings and full siblings present • With adult siblings women tend to be “kin keepers” • Looks directly at social investment • Contact • Showing care when needed (ie. Birth of child, emergency ect) • Two Hypotheses • Due to evolved psychological factors concerning investment non-related (or slightly related) siblings will show lower investment • Due to identification theory and kin selection theory , sibling relatedness with play no role in social investment. • Control for age and maternal verses paternal half siblings

  13. Face To face contact (1 year)

  14. Results • Half siblings were more likely to complain of giving and not receiving (half siblings same father, not present in maternal half siblings) • Proximity to siblings played a role however full siblings still seemed to have stronger relationships then half siblings suggesting another underlying psychological mechanism is present other then having been raised together.

  15. Differential parental investment in families with both adopted andgenetic children☆ KYLE GIBSON • Step parents and Step children • 40 times more likely to be abused and 120 times more likely to be killed by live in non-related parents (according to a Canadian study) • Full related children the relationship is based on parenting • Step parent and child relationship exists in the context of mate acquisition • Adopted children • Typically with in kin adoptions across cultures • Used as a way to control family size (evolutionary tactic) • Social climbing in the U.S • Hypothesis: parents with both a genetic and adopted child will skew resources to genetic child

  16. Used participant survey (from an adoption agency) • Mean age 57 • Mostly females responded (Mum) • Measured: • Health (braces, surgery, contact lens ect) • Education (preschool, college, tutoring, extra lessons) • Personal (car, vacation, wedding) • Time (homework, boy problems, assistance with work/ school applications)

  17. Results • No difference in health • Adopted children received better education and time commitments from parents • Failed to support hypothesis • Skewed towards adoptees not genetic children • Due to the fact they had more health problems “squeaky wheels gets more grease”

  18. Why Have Friends? Reciprocal Altruism Food Examples Information Exchange (gossip) Emotional ‘tit for tat’

  19. Baboons: What are Friends For?Barbara Smuts Promiscuous mating (non random) Monitored non-mating females Social bonds through grooming to define friendship Proximity during foraging Older man = more friends Females gain protection Attacks Males gain a possible mate Offspring