AN234 Exam #3
Red Queen Hypothesis
sexual reproduction helps organisms evade fast-breeding (and, therefore, fast evolving) parasites - example: snails (P. antipodarum) population with both sexual and asexual reproducers - long-term study showed that as parasitism increased, asexual reproducers died off sex appears to be a counterstrategy to keep up with rapidly evolving parasites and pathogens - creation of unique genotype for each offspring - hence "good genes" are the ones that confer parasite and pathogen resistance
why have sex at all?
sexual reproduction is costly 1. only half your genes passed on 2. disrupting successful genotypes is costly 3. mating is costly - time, energy, danger the Red Queen Hypothesis: sexual reproduction helps organisms evade fast-breeding (and, therefore, fast evolving) parasites
local adaptation
all living humans are of the same species; however, groups have lived in certain areas for thousands of years. - selection pressures in the local environment over long periods of time can create local biological adaptation - examples - adaptation to different latitudes - adaptations to climate - adaptations to altitude
parental investment
anything that a parent does for a particular offspring that helps the offspring and reduces the parent's ability to invest in other offspring - ultimately, why do males invest? - when it is in their best reproductive interest - bi-parental investment is more likely to evolve in species with helpless young - human infants are exceptionally helpless and take a long time to reach reproductive age
variance in men's reproduction
because males' reproduction is limited by access to mates, and females do not have to mate with different men to conceive, men's reproductive success is more variable
paternal investment
bi-parental investment (social monogamy) in humans - males form long-term pair bonds with females, know who their offspring are (usually), and invest heavily in their offspring - paternal investment and monogamy slow men's maximal reproductive rate down - are humans monogamous? two main sources of potential information: 1. comparison of human mating with close primate relatives 2. analysis of human sexual dimorphism
grandparenting
biases in investment of second-degree relatives based on paternity uncertainty - paternal grandparents have lower paternity certainty
environmental heterogeneity in fitness optima
heterogeneity: the state of being heterogeneous - diverse in kind or nature - humans have been exposed to a wide array of diverse environments (with different selection pressures) - what is adaptive may differ depending on the environment selection can favor different levels of a personality trait in different environments - ex. The 7R (long) allele of the DRD4 (dopamine receptor) gene - associated with novelty seeking, extraversion, and risk-taking - also associated with ADHD in humans - dopamine strongly associated with exploratory activity and locomotion speed/energy in rats
MHC heterozygotes and attractiveness
heterozygotes were rated as more attractive than homozygotes - attractiveness as a proxy for health
status compared to non-human primates
higher status translates to much higher reproductive success in nonhuman primates - humans form long-term pair bonds - men's reproductive rate is slowed by bonding to one mate - humans form long-term pair bonds - men's reproductive rate is slowed by bonding to one mate
universality vs. individuality
how do we reconcile a "universal" human nature with widespread human variability? - "universal" means species-specific - universality and individuality are not incompatible
group formation
humans are inclined to assume the social world is defined in terms of groups and to look for correlates ("badges") of group membership - assumption: membership = alliances - badges: - age* - sex* - political affiliation & opinion - skin color - speech - dress - food choice/prohibitions
mating systems in apes (our closest primate relatives)
humans don't fit... - live in multi-male, multi-female groups, where individuals strive to achieve status - form long term pair bonds
evolutionary medicine
if our physiological and psychological systems were designed by natural selection over millions of years to optimize survival and reproductive success, then: - why do we still have disease? - why do we do things that are detrimental to our fitness? the application of modern evolutionary theory to illness, disease, and health - the goal is to understand why we get sick - why did natural selection leave us so vulnerable?? proximate: - conventional medicine - focused on the "how" - treatment as goal ultimate - evolutionary medicine - focused on the "why" - understanding and explanation is the goal - not a method of practice - adding evolutionary theory to medicine
costs of being social
larger groups more visible to predators - larger groups need more food, so more competition for food - increased competition for mates
chromosomes come in pairs
locus: place on the chromosome where alleles are found (like an address)
why do people care about fidelity?
genes and parental investment: important fitness enhancing qualities that we get from our mates - genes and parental investment are (largely) linked for females...but they aren't for males - "paternity certainty" - the degree to which males can be confident that the offspring their investing in is their own - the primary reason why paternal investment is so rare across species
ultimately, what can humans expect from a mate?
good genes
sex differences in reproductive rate
males have a faster potential reproductive rate because male reproductive success is less limited than female reproductive success - what are females limited by? parental investment
product-consumption
males: - in foraging populations, men produce more than they consume females: - deficit until age 45 - surplus during post- reproductive years
jealousy studies
men and women asked to picture themselves in a serious, committed romantic relationship - they were presented with two alternative scenarios: 1) their partner forming a deep emotional attachment to someone else 2) their partner having sexual intercourse with someone else
intrasexual selection
men are larger, more muscular, and more aggressive than women - this suggests a history of intrasexual competition over access to women
explanatory frameworks in ev med
mismatch hypothesis - competition/coevolution with fast evolving organisms - every trait is a trade-off (life history theory) - organisms are shaped for reproductive success, not necessarily health/long life/happiness per se. - some illnesses are a product of evolved defenses and therefore are not "disorders"
naturalistic fallacy
naturalistic fallacy (i.e. error): - what is "natural" (or adaptive) is "good" (in a moral sense) - natural selection is amoral
naturalistic fallacy
naturalistic fallacy (i.e. error): what is "natural" (or adaptive) is "good" (in a moral sense) - natural selection is amoral - we decide our moral code - natural selection can help us to understand our vulnerabilities
why would we care about UV?
why we want more UV: - UV assists in the production of Vitamin D. - why we want less UV: - skin damage from UV can lead to skin cancer. - folate is depleted with increased exposure to skin light - what you'd want is just the right amount of UV... how to get just the right amount? - melanin controls the amount of UV radiation that penetrates the skin. - people produce different amounts of melanin in their skin cells --> differences in skin pigmentation
reward mismatch
our reward systems in the brain are designed to make us feel good when we are advancing our reproductive success - sex and love - social inclusion - food - winning/status in the present: we've created drugs hijack reward systems in the brain - "drugs of abuse create a signal in the brain that indicates, falsely, the arrival of a huge fitness benefit" -Nesse & Berridge (1997)
"Can race be erased?" (Kurzban)
participants show 8 photographs with sentences below them that formed a story about a coalitional conflict - sentences included verbal cues to coalition membership (e.g. "you were the ones that started the fight.") - each coalition had 2 darker-skinned individuals and 2 lighter-skinned individuals. - surprise recall test. - when participants misremembered coalitional membership, they did so using skin color second experiment: like the first, except coalitions wore different t-shirts - participants didn't pay as much attention to race - our tendency to encode race results from a misfiring of adaptations for detecting coalitional alliances
paternity uncertainty
paternity vs. maternity certainty - the degree to which a parent can be certain that the child to which they're directing PI is their own - varies across human populations. - ex. Ache of Paraguay - partible paternity paternity vs maternity certainty - the degree to which a parent can be certain that the child to which they're directing PI is their own - variation across cultures in: - who provisions moms? - what do men do with their resources?
ovulation and women's preferences
women are particularly attuned to indicators of "good genes" when they are most likely to conceive: during the ovulation window - meta-analysis showed robust cycle shifts (50 studies) - occurred when women rated "short-term" ( but not "long-term") attractiveness of: - MHC divergence - symmetry and scent cues of symmetry - masculinity: body (almost significant for facial and vocal) - behavioral dominance
Hunter-gatherer "massacre"; 10KYA
evidence of 27 individuals who met violent deaths
sexual dimorphism
sexual dimorphism reveals the degree of polygyny in a species - e.g. gibbons vs. gorillas
fast vs. slow life history strategies
"fast" life history strategy: living for the "now"; live fast, die young - faster development and less restricted "sociosexuality" in females: - earlier menarche (i.e. first menstruation) - higher reproductive hormones (e.g. estradiol) - shorter period of adolescent subfertility - earlier ages of first sexual intercourse, first birth steep "time discounting" and "risky" behavior - negative evaluations of men's investment (in females) - lower educational and occupational status/aspirations - engage in more aggressive/delinquent behavior as adults - less healthy lifestyle (more likely to smoke, eat unhealthy food) - heavier, carry more body fat associated with environments with high variability, mortality, uncertainty. calibrated during development. - unstable living environments - mortality of peers and siblings - poor relationships with parents - unstable relationships with parents - realistic appraisal of a shorter time horizon?
coalitional psychology
- a set of psychological programs that evolved to regulate within-group cooperation and between group conflict - what are the features of coalitional psychology? - easy to activate a coalitional mindset - sherif: Robbers Cave experiment (1950s) - 12-year-old boys went to camp at Robbers Cave SP. - similar background - randomly assigned to two groups and engaged in competitive activities sherif: Robbers Cave study - elicited strong coalitional psychology: - signals of coalitional membership: groups adopted names and symbols to differentiate them from the other group - in group favoritism - out group bias - bringing the groups together to work toward a common goal reduced coalitionary behavior and prejudice
mixed mating strategies
- because males invest in offspring and their reproductive rate is slowed to that of females, we can predict that males will also be choosy (at least about their long term mates) - men and women have different criteria for evaluating "long-term" mates versus "short-term" mates
latitude --> sun exposure
- close the equator = more ultraviolet (UV) radiation from the sun
why isn't warfare more common across species?
- defection and free-riding are important risks. as in the Prisoner's Dilemma, the problem of defection must be "solved" - ex. Turkana - Sarah Mathews - Turkana warfare one solution: punishment - inflict costs on free-riders (those who don't participate in the risks, but partake of the rewards) - verbal or resource sanctions - physical punishment - cooperation is higher when there is a system in place to punish free-riders - leadership or institutional control isn't necessary to sustain large-scale cooperation
in the EEA, it would have been adaptive to:
- desire foods high in fat, sugar (both rare in the environment), and salt (a necessary electrolyte) - in general, to use our taste as a guide to what to eat - experience considerable reward when eating these foods - attempt to minimize effort when obtaining food -
good genes
- genes that confer better parasite and pathogen resistance indications of good genes/health: - visual cues: facial attractiveness - age - symmetry - consistent color - high carotenoid content - sexual dimorphism - smell (MHC) genes that confer better parasite and pathogen resistance - indications of good genes/health: ¤ Visual cues: Facial attractiveness n Age n Symmetry n Consistent color n High carotenoid content n Sexual dimorphism ¤ Smell (MHC) ¨ Beauty is in the mind of the beholder
in-group favoritism & out-group derogation
- in-group favoritism: The tendency to favor people we regard as members of our own group over those we classify as belonging to some other group - more positive evaluation of in-group members and products - unequal distribution of rewards. Ex: - ingroup gets 6, outgroup gets 4 (preferred choice) - ingroup gets 7, outgroup gets 10 - occurs even when group assignments are temporary and trivial - out-group homogeneity effect: We see members of our in-group as unique individuals, and members of the outgroup as all being identical - out-group derogation
benefits of being social
- mates usually easy to find - more individuals to look for food - more individuals to defend food - better defense against predators
personality
- openness to experience: curious broad interests, creative - conscientiousness: organized, reliable, hard-working - extraversion: sociable, forceful, active, talkative. - - extraversion continuum (approach—avoid) is the most basic component of personality across species - agreeableness: good-natured, trusting, helpful. - neuroticism: worrying, nervous, emotional. - study of hunter-gatherers showed only a Big Two: "prosociality" and "industriousness"
why is skin color treated as a "badge"?
- our ancestors would have been unlikely to encounter individuals with differing skin color in the EEA - so why do people pay attention to skin color? - Kurzban, Tooby, & Cosmides: People (mis)read skin color as a badge of coalitional membership/alliance
why is paternal investment so rare in mammals?
- paternal uncertainty: the degree to which a parent can be certain that the offspring to which they're directing PI is their own - also, there may be additional survival benefit to father investment in our species
frequency-dependent selection
- the optimal strategy depends on the frequencies of other strategies in the population - example: large diversity in MHC genes - better to have a diverse immune system "toolbox" that is not exactly like others in your species ex. male scorpion flies two strategies: - hunting males offer nuptial gifts to females - deceiver males pretend to be females, steal the hunting males' gifts, and then offer the gifts to other females potential example in humans: psychopathy - characteristics: deceitfulness, lack of empathy and guilt, - impulsiveness, antisocial behavior - could psychopathic behavior ever be reproductively advantageous? - why did empathy and guilt evolve? frequency-dependent selection: extreme cheating only works when everyone is trusting - how many psychopaths could a trusting population support? 0.5-1%
two types of nature/nurture questions
1) why is my skin this color? - 100% Genes AND environment: Interaction between genes and environment that has been pre-programmed by natural selection 2) Why do people differ in the color of their skin? - cake analogy
MHC preferences
1. choose individuals that are more dissimilar in MHC alleles - mate choice unique to the chooser. 2. choose individuals that are heterozygotes over homozygotes - mate choice agreement across choosers
skin cancer risk
Australians: fair-skinned (i.e. Northern latitude) people living in a tropical environment (with an outdoor-oriented lifestyle)
political beliefs as badges of group membership
Dan Kahan, Yale Law School - how does political identity/ideology affect reasoning/cognition? - "Identity-protective Cognition": when political beliefs become badges of group membership, individuals' normal reasoning abilities become disabled
evidence in support of Westermarck
Israeli kibbutzim: - children were reared, from a very early age — the first few months — with other children of the same age in peer groups - children eat, sleep, play, bathe, with members in their own peer group - Spiro (1963) observed no cases of marriage within a peer group even though there were no sanctions against it. In fact, parents reported that they would have preferred such marriages - 125 couples in 2 kibbutzim: - not one couple consisted of individuals reared together in the same peer group from birth - of 2,769 marriages, only 13 (.05%) couples were from the same peer group - in 8 of these 13, partners became members of the same peer group after the age of 6 - in the other 5, the time spent together in the same peer group was never more than 2 years of the period from birth to 6 years of age - suggests a critical "imprinting" (i.e. learning) period of some sort exists during the first 6 years of life — in order for this aversion to appear, individuals must be exposed to one another for 4 of the first 6 years of life
more incest avoidance
Lebanese parallel cousin marriage - cultural preference for father's brother's child as mate - Lebanese parallel cousin marriage - preference for father's brother's child as mate - fathers typically live close to brothers, and children grow up together - lower fertility and higher divorce rates than other types of marriages - cultural beliefs and practices can sometimes come into conflict with evolved human psychology
The "architecture" of human kin detection
Lieberman, Tooby, and Cosmides (2006) - facultative regulation of behavior based on kinship
MHC
MHC = Major Histocompatibility Complex - genes that impact the immune system - parasites and pathogens are an important selection pressure in human evolutionary history - MHC loci are the most variable part of the genome (tons of different alleles—i.e. versions of genes) - many people are heterozygous for MHC alleles - heterozygous: 2 different alleles - being a heterozygote is good for survival and reproduction - among HIV-infected humans, heterozygotes (those with different alleles) had better survival - in a study of humans, MHC-dissimilar mates had greater fertility being an MHC heterozygote is good for survival and reproduction. - therefore: we should be selected to choose mates with MHC alleles that are different from our own
life history strategies
Stanley Burrell (aka MC Hammer) - peak: earning 33 million/year (1991) what he spent it on: - entourage of 200 (costing 500K/month) - mansion (gold-plated gates, etc.) - 21 racehorses bankrupt by 1996 - 78% of former NFL players have gone bankrupt - 1/3 of lottery winners go bankrupt two general life history strategies across species: - fast life history - slow life history - think of these as ends of a continuum
Warfare among the Yanamomö
Napoleon Chagnon - Yanomamö raiders kill men, abduct reproductive-age women, and take them as wives - 30% of men are killed by other men - 44% of men have killed someone Yanomamö men who had killed an enemy had 3x as many wives and 3x as many children as those who had not - killers are held in respect by group members - other motives: revenge for previous killing or abduction (resources?)
how we choose mates with MHC alleles that are diff from our own
T-shirt studies - men and women wear a clean t-shirt for two nights - raters smell the t-shirts and rate the smell for pleasantness results: - individuals rated the t-shirts of individuals as more pleasant when their MHC alleles were divergent
Westermarck & childhood coresidence
Taiwanese sim-pua marriages (aka minor marriage) - baby girl adopted into future husband's household, raised with him (ended in the 1970s approx.)
mixed reproductive strategies
female mixed reproductive strategy - if good genes and investment can't be found in the same person, get genes from one male and paternal effort from another - male mixed reproductive strategy - put substantial investment into one long-term mate, but also pursue short-term mating opportunities
WHR
Why is hip and thigh fat attractive? - evolutionary perspective: - men who attended to hip and thigh fat had greater fitness than those who ignored hip and thigh fat. why? - women who had greater hip and thigh fat had greater fitness than those who had less hip and thigh fat. why? - humans differ from other primates in body fat 1. primates don't really have hip and thigh fat 2. no sexual dimorphism in hip and thigh fat this is not the case in humans: reproductive-aged women deposit fat differently than men Dr. Gaulin's argument: - menarche (age at first menstruation) depends on fat distribution, not total fat - each successive offspring depletes hip and thigh fat (relative to upper body fat) - hip/thigh fat and abdominal fat have opposite effects on the supply of two LCPUFA's (LCPUFAs: long-chain polyunsaturated fatty-acids—i.e. omega 3 fatty acids like DHA found in fish, for example) - hip and thigh fat: more LCPUFAs - abdominal fat: less LCPUFAs - LCPUFAs are critical for fetal and infant brain development! - why is hip and thigh fat attractive? - evolutionary perspective: - men who attended to hip and thigh fat had greater fitness than those who ignored hip and thigh fat. why? - they preferentially mated with women who were better able to support fetal brain growth - women who had greater hip and thigh fat had greater fitness than those who had less hip and thigh fat. why? - they were better able to support fetal brain growth - not just about calories, otherwise we'd see sexual dimorphism in fat in other primates
adaptation vs. "susceptibility"
adaptation - ex. sun tanning - susceptibility (aka maladaptation): a failure to respond to the environment; when adaptations are not designed to accept certain inputs, and the body is damaged as a result - ex. sun burn - obesity?
facultative traits
adaptations that require input from the environment - ex. sun tanning ability - input from the environment: presence of Uvb - output: increase in melanin - think of facultative adaptations as "if....then..." programs traits that respond to the environment - emotions are facultative, could personality also be facultative? but what is it contingent upon? - ex. extraversion - extraversion: sociable, forceful, active, talkative - approach/avoid dimension in other species ex. Extraversion - self-rated physical attractiveness significantly predicts extraversion - may also change in response to self-perceived social status - facultative adaptations as "if....then..." programs - extraversion may be a personality that capitalizes on the benefits of social interaction - introversion capitalizes on the costs of social interaction
adaptations may be out of date (recap)
adaptations we see in the present are here because they survived the challenges of the past - environments change, but the pace of evolution is slow - therefore, adaptations may be out of date
changes in life history strategy across the life course
adolescents (esp. young, single males): Fast(er) strategy - males: higher testosterone à risk-taking, competition for mates and status. - fathers: slower strategy - marked by decrease in testosterone with entrance into committed relationship and with the birth of child - having children decreases men's testosterone
men's preferences for physiological investment
age - women's fertility declines with age - men's preferences for age in a mate: 20-25 - as men get older, they prefer mates who are increasingly younger - teenage males prefer slightly older women (i.e. college aged) - 37 cultures study: in every culture, men preferred younger (vs. older) wives - preferences for facial attractiveness by men: youth - youth signals current fecundity (probability of conception) as well as future fertility (number of offspring) - men place greater emphasis on physical attractiveness in mates across 37 cultures (Buss, 1987)
what makes a face attractive?
age, symmetry, consistent color (make-up increases both perceived symmetry and health) - group of UK researchers found that high fruit and vegetable content changed skin color - carotenoids in the skin from diet - the "golden" color was perceived as most attractive (more attractive than color due to tanning) - averageness - tend to be more symmetrical masculinity/femininity - linked to sex hormones during development - male sex hormones (e.g. testosterone) are thought to signal health because they may be immunosuppressive - female sex hormones (e.g. estrogen) are associated with age & fertility
slow life history strategy
characteristics: - larger body size - later reproductive maturity and first birth - few offspring - high parental investment - low offspring mortality - longer lifespan often found in environments with low extrinsic mortality (e.g. predation) rates because: - investment in the body and in offspring paid off for these individuals—they got more genes into the next generation than those that went fast
fast life history strategy
characteristics: - small body size - early reproductive maturity - many offspring - little parental investment - high offspring mortality - short lifespan - often found in environments with high extrinsic mortality (e.g. predation) rates because: - long-lived individuals were selected against; those that reproduced quickly passed more genes to the next generation
why isn't warfare more common across species?
chimpanzee warfare is instrumental - it leads to annexation of territory --> more resources
when "should" we expect intergroup conflict to occur?
contested, zero-sum resources (real or perceived) - resource scarcity (real or perceived) - especially when people feel they have "nothing to lose" - mechanisms in place that support large-scale cooperation - punishment
two routes to status in humans
dominance - status attained by one's ability to inflict costs on others through force or threat of force prestige - status attained by one's ability to confer benefits (e.g. knowledge) to followers
dominance hierarchies (are transitive)
dominance hierarchies emerge from social competition for zero-sum, contested resources (food, mates, territory) - preferential feeding and mating access --> higher fitness - transitive/linear: if A defeats B and B defeats C, A is automatically dominant to C - positional: rank is relative - rank shifts over time
what humans can expect from a mate
females want: - parental investment (economic + care) - good genes - fidelity (keeps resources at home) - partnership males want: - parental investment (physiological + care) - good genes - fidelity (keeps paternity at home) - partnership
asymmetries in parental investment
females: - egg: large (relatively) and limited in number - gestation - lactation males: - sperm: cheap and plentiful
dominance hierarchies
fighting is very costly, so individuals use signals of fighting ability to decide dominance status
female preferences for investment
financial prospects rated more important by women than by men in 37 cultures (Buss, 1987)
coresidence --> secondary cue
duration of childhood co-residence: - Westermarck hypothesis - prediction: the longer you co-resided with another individual during childhood, the more likely you are to encode that individual as a relative - when hunter-gatherer bands "fission and fuse," nuclear families stay together
prestige also leads to reproductive success
effect of dominance and prestige on offspring survivorship among the Tsimane
status in hunter-gatherer//EEA
even "egalitarian" societies show differences in status - some individuals have more say over group decisions, gain more respect from others, are more sought after as mates, etc.
which cues does kin detection system evolve to take as input?
evidence so far... - maternal perinatal association? (yes) - duration of childhood co-residence? (yes) - paternal perinatal association or co-residence? (no) - other childhood behaviors? (co-sleeping, meals, play?) (no) - phenotype matching? MHC complex? facial similarity? (?) - what people tell you? (no)
mate guarding
evolutionary function of jealousy - guard against mate's mixed reproductive strategy - both sexes experience jealousy but MRS theory suggest their jealousy would more often be triggered by different risks - females: guard against partner's emotional engagement - females: guard against partner's sexual engagement
heterogeneity in the social environment
examples: - extraversion - pros: social benefits, e.g. mating, cooperation - cons: social costs, e.g. illness, social conflict - extraverts suffer from more illness and injury - neuroticism pros: increased vigilance for dangers cons: health problems due to prolonged stress - characteristics may be "calibrated" over development - 'given condition x, pursue behavioral strategy y'
cooperative coalitions
examples: - large game hunting - food sharing - building shelters - launching a raid on another group (warfare) - defending against attacks from another group (warfare)
individual differences
on which dimensions do we vary? - every dimension! - personality refers to the ways we differ psychologically
differences between now and the EEA
no fat- and sugar-dense foods - fruits and vegetables bred for high sugar content and large size but low in nutrients and fiber. - ex. Wild Sikkim apple (native to Nepal) has 100x more phytonutrients than our favorite apples - small and barely sweet no fat- and sugar-dense foods - leaner game meat (with high omega-3 fats) vs. domesticated feed-lot animals bred for high fat content no "flavorings" - what is flavor? - the sensory impression of food or other substance, and is determined primarily by the chemical senses of taste and smell no "flavorings" - what is flavor beyond salty, sweet, bitter, sour, and umami? - secondary plant compounds: chemicals produced by a plant to repel or attract herbivore/omnivore - part of a larger class of molecules called volatiles Goff & Klee, Science. (2006) - tomatoes produce over 400 volatiles, but only a small number are detected and preferred by humans - almost all are derived from essential human nutrients - no "flavorings" - flavorings mimic plant secondary compounds - no Doritos in the EEA - mismatch between flavor and nutrition: in the EEA, flavor and nutrition were effectively the same thing. no supermarkets, no takeout, no Cuisinarts - all food is obtained with considerable caloric expenditure - exercise every day: hunting, gathering, Food processing, child care - hunter-gatherers don't go jogging after work! no obesity (or chronic disease) in mobile foraging populations - could the health problems associated with obesity ever have been a significant selective pressure if no one was obese?
ecological mismatch
novel ecology - light regulates our circadian rhythms. - relative presence of blue light indicates the day/night transition - novel ecology - light exposure and sleep - exposure to blue light at night disrupts sleep patterns - in the present: mismatch between light exposure and natal skin color - office work, then one week out in the sun per year, clothing - people living at different latitudes than their ancestors
Maternal Perinatal Association (MPA --> primary cue)
observing your biological mother caring for a neonate - if your mother is taking care of an infant, it is likely to be your sibling - only works for older sibs detecting younger sibs
Lieberman, Tooby, and Cosmides (2006): predictions
older sibs detecting younger sibs: • MPA • not co-res - younger sibs detecting older sibs: • MPA unavailable • co-residence duration is best survey measures of sib-directed altruism and sibling incest aversion: - altruism toward a particular sib: - how many favors did you do for this sibling in last month? (behavioral) - would you donate a kidney to this sib? (attitudinal) sexual aversion: - degree of disgust at prospect of sexual contact with a specific sibling (passionate kissing, sex) Rank & Likert measures - moral opposition to third-party sibling incest - byproduct of personal disgust — an unobtrusive measure - results show that when MPA is absent, individuals use coresident duration as a cue to kinship
kin selection
one of two explanations for apparent altruism (the other is reciprocal altruism)
status is positional in humans
people strive for relative status, not absolute wealth, dominance, or prestige - arms race for positional goods (Robert Frank) - positional goods: things you can see - non-positional goods: 401K, savings account, vacation time - arms race for positional goods - two options: A. you live in a 4000 sq ft house and others will live in a 6000 sq ft house B. you live in a 3000 sq ft house and others will live in a 2000 sq ft house people strive for relative status, not absolute wealth, dominance, or prestige - arms race for positional goods - mismatch: - humans in developed countries have ample time to pursue status because we don't have to spend all day foraging - sedentary, settled lifestyle allows the accumulation of goods - economy of scale allows some to amass much more wealth than others
heritability
personality and intelligence (and other measures of psychological variability) have moderate "heritabilities" (0.35 < h2 < 0.65) heritable and heritability are different (but related) concepts!! - heritable: whether or not a gene or trait can be inherited - heritability: the proportion of phenotypic differences that is due to genetic differences two sources of variation - differences between individuals can arise because: A. they have different genes B. they have different experiences - heritability is a method to "partition" (i.e. divide up) the differences between people into genes vs. environmental effects - how much of the phenotypic differences between individuals: - is due to the fact that they have different genes? - and how much is due the fact that they have different experiences? - method: twin analysis. comparing identical twins (reared apart and together), fraternal twins
why is there variation in facultative traits?
potential reasons: 1. facultative traits 2. life history trade-offs 3. frequency-dependent selection 4. environmental heterogeneity in fitness optima 5. selectively neutral 6. sexually produced variation around polygenic optimum 7. spatial or temporal variation in selective regime
why is there variation in heritability traits?
potential reasons: 1. facultative traits 2. life history trade-offs 3. selectively neutral 4. sexually produced variation around polygenic optimum 5. spatial or temporal variation in selective regime 6. frequency-dependent selection 7. environmental heterogeneity in fitness optima
challenges (in terms of maximizing reproductive success) for ancestral females
quality - female reproduction is limited by her physiological investment capacity (energy gestation, lactation) - produces adaptations for maximizing quality - prediction: females will desire a smaller quantity of mates and will be more choosy.
challenges (in terms of maximizing reproductive success) for males
quantity - male reproduction is limited by access to fertile females - produces adaptations for maximizing quantity - prediction: males will desire a greater quantity of mates and will be (relatively) less choosy
evolutionary personality psychology
requires reframing - personality as strategic individual differences - environment as distributions of adaptive problems
social mismatch
social environment in the EEA: - few people (50-300) - mostly relatives - wide range of ages. lots of children, and relatively few individuals your own age - child-bearing starts after adolescence - relatively few possessions, mostly egalitarian - no way to know about the world beyond the people you talk to; no media exposure social environment in the EEA: - few people (50-300) in the present: novel social environment - lots and lots of people, mostly unrelated - college: thousands of people your own age - wide variation in wealth and possessions - media: lots of very beautiful people - result (e.g.): - cues of increased competition for status and mates - social stress: anxiety and depression in the EEA, our assessment of risks and dangers were based on what we observe around us - in the present, media amplification of risks - people overestimate rare risks and underestimate the common risks
where did status hierarchies come from?
sociality: humans and many other non-human primates aggregate in social groups
mismatch and depression
status and mate competition - facebook and depression - more Facebook use --> Higher levels of depression - effect seems to be driven by the passive consumers, not the active engagers - social comparison and impossible ideals - celebrities as pseudo-neighbors
women are more attractive to men during ovulation as well
study on lap dancer tips across the menstrual cycle
chemical senses: taste
taste receptors reveal something about the food: - simple carbohydrates --> sweet --> calories (+) - sodium --> salty --> essential electrolyte (+) - diverse chemicals --> bitter --> toxins (-) - acids --> sour --> spoiled (-) - amino acids --> umami --> protein (+) - fatty acids --> texture, mouth feel --> fat (calories) (+)
our intellectual baggage
the "debate over human nature": Hobbes vs. Rousseau - Hobbes: "nasty, brutish, and short" - Rousseau: Man is essential "good"
status
the position or rank of an individual (or group) within a society - authority, cachet, dignity, dominance, eminence, esteem, face, position, preeminence, prestige, rank, regard, repute, respect, standing, stature... - people treat status as very important
additional mating benefits men more than women
throughout history, high status males have had a large number of offspring - ex. Moulay Ismail, "the bloodthirsty" - currently holds a record for the most documented offspring, 867 - ex. Ghengis Khan - 1 in 200 worldwide (and 10% in Mongolia) are (likely) his descendants
sexual selection in humans
to what extent does this apply to humans? - date solicitation experiment - confederates asked unsuspecting subjects for a date - variable: coffee, apartment visit, sex. - acceptance rate? Women Men Coffee 50% 50% Apartment 6% 69% Sex 0% 75%
sexual selection
type of natural selection. - sexual selection builds adaptations that increase mating success: 1. more mates 2. better mates
dominance signals in humans
universal non-verbal displays of pride - performed by blind people - voice pitch - in one study, males who perceived themselves to be dominant lowered their voice pitch when addressing a potential competitor
nature/nurture dichotomy
very common story in science writing: does genetics or learning matter? and which matters more? - what we've learned so far about the nature/nurture dichotomy: - nature/nurture dichotomy has no utility when it comes to explaining the traits of individuals - 100% of both genes and environment. - ex. calluses, language - "nature wrote the rules for how nurture works" nature/nurture dichotomy does have some utility when it comes to explaining differences between individuals
warfare
warfare occurs across cultures and throughout history - warfare occurs across cultures and throughout history - wide variance in the amount of warfare - overwhelming it is the activity of men
personality psychology
what is personality? - interaction style -- behavioral biases - stable - context-general most common personality framework: - Big-Five model: OCEAN - atheoretical
male-male homicide
why do men kill other men? - "incidents of trivial origin" - what is this? status
inter-group relations
why do people form social groups? - protection and defense - foraging and mating efficiency - cooperation - cooperative coalitions: alliances of more than two individuals for the purpose of collective action to achieve a particular goal what limits the size of groups? - resource availability
mismatch hypothesis
why do we behave in ways that are detrimental to our fitness? - massive quantities of salt, hydrogenated industrial oils + sugar, and low vegetable intake --> obesity, cardiovascular disease, diabetes, etc. - little exercise --> obesity, etc. - smoking, drug use --> Lung cancer, addiction - risk taking (unprotected sex, speeding, etc.) many behaviors that appear maladaptive are the consequence of a mismatch between our modern environment and the environment in which we evolved (EEA) - EEA: environment of evolutionary adaptedness adaptations exist because they helped our ancestors survive and reproduce - what ecology shaped our modern behavioral and dietary preferences? - hunting and gathering environment diet/flavor mismatch - activity mismatch - ecological mismatch - (sun)light exposure - pathogen exposure - reward mismatch - social mismatch
incest avoidance (detecting kinship)
why do we find mating with siblings so repulsive? - Freud: we actually want to mate with family members, but cultural taboos keep us from doing it - evolutionary biology: natural selection selected against incest behavior - mating with siblings is bad for reproductive success: - evolutionary biology: children of incest have a higher chance of congenital diseases and deformities - what if you had a rare genetic mutation, s, that causes disease in the homozygous condition only? - there is a 50% chance your sibling also carries the harmful mutation --> increased percentage that your offspring would have it
are humans monogamous?
yes? humans form longterm bonds (unlike close primate relatives) - mating is done in private - fathers often invest in their offspring no? - sexual dimorphism in body size, muscle mass, aggressive behavior - 85% of societies allow polygyny - in one study, 23% of women in the US reported having at least one affair in their life - divorce and remarriage: defacto polygyny (men are more likely to remarry) - intermediate testes size extra-pair mating + defacto polygny + sexual dimorphism: suggests a history of mild polygyny in humans - however...paternal investment is a VERY important feature of the human mating system
