Who are you?
Write down the first 10 descriptions of yourself that come to mind. Try to work as quickly as possible.
Defining Family
Emlen (1995) described two types of families: simple families & extended families
both of these definitions hinge on the presence of a reproducing female What about homosexual couples?
Only 3% of all bird and mammalian families live in family groups
living with families is detrimental to reproduction
The Evolution of Families
Ecological Constraints ModelFamilial Benefits ModelConditions necessary for the evolution of
families: more offspring than reproductive vacancies offspring must wait for reproductive vacancies
until they have the required attributes to compete for mating positions
benefits of staying with the family must be large
Predictions of Emlen’s TheoryRegarding kinship and cooperation
shortage of reproductive vacancies more resources, more stable families more assistance in child-rearing in families sexual aggression is low
Regarding changes associated with the elimination of a breeder conflict concerning the appointment of a successor breeder who is not genetically related will increase
sexual aggression
clip: Steven Pinkerhttp://video.google.com/videoplay?docid=3554279466299738997&q=siblings+%2B+evolutionary+psychology&hl=en
Origin of Kinship Altruism
Reciprocity demands familiarityin ancient times, familiarity meant
kinshipkinship altruism = manifestation of
reciprocal altruismHow far-reaching are the effects?
Inuits = strongest non-kin relationship < weakest kin relationship
understanding among non-kin
Studying Kinship
Families are more difficult to study than strangers
extended families don’t live near one another
favoring kin seems normalnepotism challenges Western
principles
Inclusive Fitness Theory
An individual’s own reproductive success plus the reproductive success of relatives as weighed by the degree of genetic relatedness
Altruism - a behavior that results in costs to the self and benefits another
Hamilton’s Rule:c < rb
c = cost to individual r = degree of genetic relatedness b = benefit to other person
Genetic Relatedness
Identical twin = 100%Sibling = 50%Parent = 50%Grandparent = 25%Aunt/Uncle = 25%Cousin = 12.5%Great Aunt/Uncle = 12.5%Great Grandparent =12.5%
Hypotheses about Kinship(from Daly, Salmon, & Wilson, 1997)
Ego-cetered kin terminology
Distinctions regarding sex
Distinctions regarding generation
“Closeness” associated with genetic relatedness
Hypotheses about Kinship(from Daly, Salmon, & Wilson, 1997)
Elder members will encourage altruism towards collateral kin clip: “Gilmore Girls”
Position within kin network becomes a part of self-concept
People know who their “real” kin areKinship terms produce illusory feeling of
connectedness between unrelated people
Alarm Calling in Squirrels
Alerted squirrels benefit, but the alarm caller is in trouble
potential explanations: predator confusion hypothesis predator deterrance hypothesis reciprocal altruism parental investment inclusive fitness hypthesis
can these findings be applies to humans?
http://www.agpix.com/catalog/AGPix_Read/large/AGPix_Read_0041_Lg.jpg
Helping in Humans
A study of 300 women in Los Angeles more likely to help closely related kin more likely to help those with greater
reproductive valueHughes (1988) used mathematical
analysis to show that key individuals in a society are those who have just passed through puberty now able to reproduce
Helping in Humans
Fieldman et al. (submitted) asked subjects to sit in isometric position for cash reward
performed on successive daysrecipient of reward changed with each
exerciselength of time subjects were prepared to
endure pain proportional to genetic relatedness of recipient
Life-or-Death Helpingstudy by Burnstein et al. (1994)
Two types of helping: substantial helping trivial helping
Two scenarios: burning house and must save one
person inside run errands for someone
Life-or-Death Helpingstudy by Burnstein et al. (1994)
Helping decreased as genetic relatedness decreased especially strong effect in life-or-death scenario
Helping in life-or-death scenario decreased with age effects of age reversed in trivial scenario
Helping is a function of genetic relatedness and age
Why were one-year-olds helped the most?
Life-or-Death Helping Clip: “The Pretender” Expansion on Burnstein et al. (1994)
measure of emotional closeness
more likely to be emotionally close with more related kin
emotional closeness correlated with altruistic behavior Are these constructs really as different as
Buss makes them out to be?
having kin in close proximity during life-or-death situations affects survival rates Mayflower and Donner party
Kitty Genovese
SiblingsParent-offspring conflictSibling conflictsiblings can be strong social
allies, but also represent competition for parental resources clip: “In Her Shoes”
adaptive problem for siblings clip: “Narnia”
SiblingsSulloway, 1996
In all societies, parents discriminate among their children
Adaptive problems create niches based on birth order oldest child: support the status quo middle child: continually trying to surpass
older children youngest child: most likely to be spoiled
clip: “Narnia”
Siblings(from Sulloway, 1996)
Strategies siblings use to procure parental resources promote parental
favor directly dominate their rivals counter domination
How does this relate to your experiences with siblings?
Patterns of Inheritance
Three predictions: genetically related kin & spouses closely related offspring rather than siblings
study of 1000 randomly selected decendents in British
Columbia recorded dollar value of estates labeled beneficiaries by genetic relatedness + “spouse”
and “nonfamily”
Patterns of Inheritance
Women distribute wealth to more people men leave everything to their spouse women did not trust men to distribute wealth older men remarry more often than older women
may divert wealth from decedent to new offspring rather than shared offsrping
older women are usually postmenopausal
92.3% wealth to spouses or family 46% to relatives sharing 50% genes 8% to relatives sharing 25% genes less than 1% to 12.5% of genes
Four times as much to offspring than siblings
Investment by Grandparents
Genetic relatedness =.25Two generations of paternity uncertaintyorder of investment:
Mother’s mother Mother’s father Father’s mother Father’s father
clip: “Gilmore Girls”
Investment by Grandparents
Discriminative grandparental investment theory
DeKay (1995) confirmed hypotheses
Euler & Weitzel (1996) results confirmed hypotheses MoFa being higher rules out
sex differences ruled out differences due to
proximity
Grief: A Measure of Selectionstudy by Littlefield & Rushton (1986)
Examined magnitude of grief when a child dies loss of inclusive fitness prospects
Self-reported measures of griefParents grieved more than distant
relativesage and health of childdifferences in grandparents’ grief
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