EBH 200: The Evolution of Human Behavior UNIT 2

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Ontonegy

the entire sequence of events involved in the development of an individual organism

Human life stages

• prenatal, before birth

• infancy, before weaning

• juvenile, before puberty

• adolescence

• adulthood, before menopause

• post reproductive adulthood

Life history

the stages of growth, reproduction, and dispersal that an individual goes through during its life

r-strategy

• changing, unpredictable environment

• large litter size

• small parental investment in individual offspring

• high offspring mortality

• rapid development and maturation

• short interbirth

• short lifespan

interbirth

time between having babies

k-strategy

• stable and predictable environments

• small brood or litter size

• large parental investment in individual offspring

• low offspring mortality

• slow development and maturation

• long interbirth intervals

• long lifespan

Why do humans have a short interbirth interval even though we use K-strategy?

due to alloparenting

advantages of being slower

• brains are energetically expensive

• culturally transmitted information

• time for learning

• spread out costs

life history trade offs

mediated by hormones

growth vs reproduction

Current vs future reproduction

Parent-offspring conflict

parents want equal investment but children want unequal, ex. breastfeeding

weaning conflict

How long mothers and offspring negotiate milk transfer

types of play

• locomotor

• object

• social

functions of play

• motor development and physical training

• learning social and communication skills

• practice skills prior to adulthood

• establish dominance relations and form affirmative bonds

• sexual learning

play in non-human primates

• Preference for same sex and same-age partners

• sex differences increase with age

play in humans

• boys: rough, locomotor, cars

• girls: fluent and perceptive, dolls

perceptual speed

ability to quickly and accurately compare letters, numbers, objects, pictures, or patterns

What accounts for sex differences in play?

• sexual selection

• group size and composition

• mating system and differences in roles

• body size and shape

• physical ability

• socialization

what causes sex differences after childhood?

physical and hormonal reasons, and parental influence

what did the ted talk about the elderly say?

• In traditional societies, elders stay with their families and are neglected until death, abandoned, killed

• In farming societies, elders are cared for and fed; they stay close

• America is biased against elders, especially since they live longer now

• use grandparents for knowledge; they ARE useful

altriusm

an individual acting in a way that will decrease his or her own survival chances and/or reproductive opportunities, but improve the survival chances and/or reproductive opportunities of another individuals

inclusive fitness

consists of direct fitness due to personal reproduction and indirect fitness due to the additional reproduction by relatives

kin selection

evolutionary strategy that favors the reproductive success of an organism’s relatives even at a cost to the organism’s own survival and reproduction

Hamilton’s rule

Altruistic behaviors will be favored by selection if the benefits to the recipient outweigh the costs to the altruist, after considering how closely related the recipient and the altruist are

Hamilton’s equation

• rB > C

• r = relatedness

• B = benefit to recipient

• c = cost

Kin selection in humans

• food sharing among close relatives

• political alliances between kin are more stable

• kin sought in times of need

• close relatives are given more expensive gifts

Polynesian adoption

Doesn’t support kin selection, adopted nieces and nephews, but is only motivated due to labor necessity

inheritance of wealth in Western culture

spouse because it also goes to the child, then dependent on the coefficient of relatedness

kin recognition

through phenotypic matching and behavioral cues

phenotypic matching

implicit assessment through traits like odor and visual cues

male baboons and phenotypic matching

• Paternity confusion due to polygynandry

• prefer their own offspring

• can differentiate between genetic and non-genetic children, but not between non-genetic and unrelated

genetic offspring

dna test confirmed

non-genetic behavioral juveniles

mated but not father

unconnected juveniles

not related and did not mate

Experiment results for behavioral cues

genetic vs non-genetic doesn’t matter, but non-genetic is differentiated from unconnected

behavioral cues

time together, mating history, interactions with other relatives

taiwanese child marriages show what cues?

behavioral

Sweaty t-shirts…again

MHCs show differences in smell, women were more attracted to men with different MHC because it allows for immune system diversity in offspring

Major histocompatibility complex (MHC)

Cell surface proteins that play a role in the immune system’s response to foreign pathogens have specific odors, play a role in disassortative mating

Macaque specieis

maternal siblings groomed more, peers groomed more than non-peer when there was one male alpha, and age based behavioral cues

westermarck effect

people who live in close domestic proximity during the first few years if their lives become desensitized to sexual attraction toward one another

mutualism

immediate gains for both parties

delayed reprocity

delayed returns; reciprocal altruism; time delayed mutualism

prisoner’s dilemma

two prisoners can cooperate and not testify against the other, or defect by testifying even if they have to lie and the other didn’t do it; both will likely defect and end up in jail

always defect

defects at every turn, safest but misses larger payoffs when the opponent wants to cooperate

always cooperate

only good when others cooperate

random method

start cooperating and then match, 50/50

axelrod’s tournament

had gamers come up with strategies for the prisoner’s dilemma

insured transactions

friendship, transactions characterized by repeated interactions

enlarge the shadow of the future

greater incentive to cooperate when theres an extended future, knowing the game will end increases the likelihood of defecting

teach reciprocity

the larger of those practicing tit-for-tat, the less successful a defector will be

insist on no more than equity

tit for tat does not insist on getting more than it gives

respond quickly to provocation

• retaliate so they know you wont be exploited

• cultivate reputation as reciprocator

public goods

shared goods that are not easily monopolized; inefficient to exclude other users, yet the use of resources by other parties decreases the resource value

the ultimatum game

• Player 1 given money to split; if player 2 accepts then they get money but if they dont then neither of them get anything

• no one offered above 50% but got closer the mosre industrialized a society was

explanation of ultimatum game results

• Traditional societies consider their own money and generosity to be unreasonable

• Industrial societies want to maintain their reputation and appear more generous

the dictator game

• no opportunity for rejection

• donations went down but industrial societies still donated the most

co op and co op reacition

gratitude

co op and defect emotion

co op feels indignation

defect feels guilt

defect and defect emotions

both shameful

guilt motivates

cooperation

status hierarchies

determines which individuals have access to resources such that higher ranking individuals have priority of access and imposes a degree of order

status hierarchies in non-humans

established and maintained through agonistic interactions

assessing dominance in non-human primates

through display of submissive behaviors

dyadic interaction

interaction between two individuals

dominance

property of social relationships, not characteristic of individuals

status hierarchies in humans

• Impacts conflict, resource allocation, mating, and coordination of group tasks

• egalitarian societies rank differences even when social harm suppresses them

• maintained through dominance and prestige

prestige

influence or standing in the eyes of others

semai communities

senior has influence but cannot control; prestige not dominance

martu of australia

men are directors, not commanding

example of prestige

athlete endorsement

dominance and prestige are not…

mutually exclusive

forager-horticulturalist tsimane of bolivia

Men ranked men

• their wives are both attractive, but prestige led to younger wives

• both have extramarital affairs

• both have higher fertility, but prestige children had lower mortality

• both remarry after divorce, but prestige has younger wives

social competition hypothesis

humans are extremely sensitive to status, used to be useful but it has pathological impacts

human behavioral ecology

fitness consequences of human behaviors, variance; humans can be adapted to their immediate environments

evolutionary psychology

design of cognitive mechanisms; modern humans are adapted to their ancestral environments

naturalistic fallacy

whatever is natural is good

moral fallacy

whatever is good is natural

socioeconomic status gradient

lower social position is associated with worse health

factors driving the SES gradient

• differences in healthcare

• education

• differences in health risks like exposure to drinking

• *psychosocial factors like stress

stress can come from

others or the environment

physical stressor

immediate external challenge to homeostasis

psychological stressor

anticipation that a challenge to homeostasis looms

stress of male baboons

most dominant have the highest stress, but afterwards stress increases as dominance increases

low income society

• low rank

• low calories

• risk of infection

• stress

• low SES

high income society

not physically suffering, but they are suffering psychologically

how to acquire resources

on your own or steal

stealing favored when

cant get resources on own or if its less costly

when not to fight thief

when you’re likely to lose to avoid injury

Are violence and aggression instinctive?

No, it’s a flexible response to local environmental conditions, knowing when to use it

how do men and women differ?

• desire for sexual variety (men want more partners)

• sexual over-perception bias (smiling = sex)

• deception

• infidelity

• breaking up

Ted Talk on men and women’s differences

• women: date > apartment > sex

• men : sex > apartment > date

• women cheat because they are emotionally unhappy

domestic violence and evolution?

men are violent to make sure their partner has their child and not another mans

conditions provoking jealousy in men

loss of paternity and infidelity

conditions provoking jealousy in women

emotional infidelity

women are more likely to be killed…when?

after divorce

younger men are…

more violent

younger women are…

assaulted more

what leads to sibling rivalry

prolonged juvenile dependence and short interbirth intervals

siblicide vs. gender

mostly male killers, same sex killing is more common

siblicide vs birth order

mostly younger killers, elder siblings start fights before puberty and switches after