Evolutionary psychology exam 3
Why do the !Kung share so much?
!Kung experience extreme variability in the availability of food and water. Sharing is a matter of life and death
Compared to non-human primates
Higher status translates to much higher reproductive success in non-human primates Because humans are different from other primates
Warfare among the Yanamomo
Napoleon Chagnon Yanomamo 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. Why? When think about warfare and if it led to reproductive success Yanomamo 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
Women are more attractive to men during ovulation as well
Study on lap dancer tips across the menstrual cycle Get more tips when ovulating
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? Coffee: women-50% men-50% Apartment: women-6% men-69% Sex: woemen-0% men-75% Men are not indiscriminate; so much more likely to have sex (even if they knew the person for an hour). At 5 years, males and females are equally likely to have sex. Clear sex difference in likeliness to have sex
Evidence for sexual selection
Trait is associated with testosterone in males Recent meta-analysis showed no relationship between testosterone and fWHR in adults This research: No clear association with T during puberty Timing of trait development coincides temporally with mating competition (for fWHR, at puberty) This research: No sex differences before, during, or after puberty
How do status lead to reproductive success?
Tsimane of Bolivia People with higher social status have better access to mates and higher mate quality (more attractive, younger, more fertile)
Theory of sexual selection (review)
Type of natural selection Sexual selection builds adaptations that increase mating success: More mates Better mates Males have faster potential reproductive rate because male reproductive success is less limited than female reproductive success Females are limited by breast feeding, care and protection, and gestation
Dominance signals in humans
Universal nonverbal 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
Life history theory and violence
Variation between groups in rates of violence may be linked to life history theory Two factors that may influence levels fo violence: The degree of social inequality Extrinsic mortality rate
Nature/nurture
Very common story in science writing: does genetics or learning matter? And which matters more? Evolutionary psychology collapses these dichotomies The article regarding nature vs nurture makes things difficult The articles like this are referring to how nature/nurture dichotomy does have some utility when it comes to explaining differences between individuals
Warfare
Warfare occurs across cultures (sporadically) and throughout history Deaths due to warfare have diminished quite substantially in modern day in comparison to the past Wide variance in the amount of warfare Overwhelming it is the activity of men. Why? Men can potentially get more mates than females. Have aggression.
Also remember
We're focusing on averages, not variation here Focus on heterosexuality
Punnett squares and Mendelian genetics
What if you had a rare genetic mutation, s, that causes disease in the homozygous condition only? Most harmful traits are recessive If you mate with your sibling, you both have a lot of the same genes and more likely have babies with messed up genes If the frequency of this rare allele was 2% of the population, the probability that your children would have this disease would be 0.5% (2% x 25%)
Personality psychology
What is personality? Interaction style. Behavioral biases. Stable Context-general Most common personality framework: Big-five model: (Goldberg 1993) OCEAN Atheoretical (there was no general theory guiding the way this model was developed) basically what they did was ask people hundreds and hundreds of questions and then used a statistical technique to see if certain questions formed a cluster. From there built a five personality framework
Examples of evoked culture
What we've already learned Paternity certainty and matrilineal inheritance Social inequality and violence Foraging variance and sharing Pathogen prevalence and mating preferences Cultures of honor
The nature/nurture dichotomy
What we've learned so far about the 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
Male-male homicide
Why do men kill other men? Incidents of trivial origin (trivial=not important). Majority of these homicides begin with something that's not a good reason. Someone started a conflict and it led to death in one of the individuals. What is this? Status.
Inter-group relations
Why do people form groups? Protection and defense Foraging 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
Life history strategy
Why do these characteristics go together? Mortality
Explanatory frameworks in ev med
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 diseases, diabetes, etc. smoking, drug use—> lung cancer, addiction Risk taking (unprotected sex, speeding, etc.)
Two types of nature/nurture questions: cake analogy
Why does this cake taste this way? 100% of both: ingredients AND cooking method (interaction). Why do these two cakes taste differently? Either due to a difference in ingredients or a difference in cooking method
In the EEA, you would have been adaptive to a;
Attempt to minimize effort when obtaining food
3D sample
3dMD digital stereophotogrammetry 24 landmarks X,y,z coordinates Make 3D representations of faces. Then have people put landmarks on face that have coordinates that allow people to make measurements of face
Bolivian Tsimance sample
91 males and 88 females Front-facing photographs Other measures: BMI, strength, testosterone (males) Clear effects: chin gets longer and nose width, nose breadth gets wider. The brow gets larger and eyebrows get larger and bushier. Also eyes get proportionally smaller in comparison to the rest of the face
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: (not just a psychological thing, physical thing too) Earlier menarche (pregnancy) 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 (in females) Lower educational and occupational status Engage in more aggressive/delinquent behavior as adults Less healthy lifestyle (more likely to smoke, eat unhealthy food) Heavier, carry more body fat If told them I'll either give you $5 now or wait a month and i'll give you $100, they'd rather take $5 now Associated with environments with high variability, mortality, uncertainty. Calibrated during development Unstable living environments Mortality of peers and siblings Poor relationships with parents Father absence when growing up Unstable relationships with parents These things set people up for fast life strategies, but not always Instead of seeing MC Hammer as super stupid, we should see him as pursuing a life strategy that would've helped our ancestors—> why wait for stuff if you're going to die soon anyway? Realistic appraisal of a shorter time horizon? "Slow" life history strategy: investing in the future Slower development, less risky behavior, investment in long-term relationships, confidence in the future
Sexual dimorphism in humans: it depends on the trait
(any number above 1 means males are larger than females) Height: not a lot of sexual dimorphism; suggests that people during evolutionary history were monogamous Arm muscle: males are 78% larger than females; there are incredibly more sex differences for males→ makes us look more like the gorillas
What do humans want from a mate?
Females want: Parental investment (economic + care) Status, wealth, ambition, motivation Good genes Fidelity (keeps resources at home) Partnership Males want: Parental investment (physiological + care) Physical investment capacity, youth, fertility Good genes Fidelity (keeps paternity at home)
Why?
//Gana San have ways to buffer variability so sharing is not as important for survival Small amount of food cultivation Including a kind of melon that stores water Goat husbandry (so they have sources of meat and milk) Sharing is not a matter of life and death The world we've created today is an extreme version of the //Gana San
Coalition also psychology
A set of psychological programs that evolved to regulate within-group cooperation and between-group conflict What are the features of coalitions 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 Ingroup favoritism Outgroup bias Bringing the groups together to work toward a common goal reduced coalitionary behavior and prejudice
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: sunburn Obesity?
Mismatch hypothesis
Adaptations exist because they helped our ancestors survive and reproduce What shaped our modern behavioral and dietary preferences? Hunting and gathering environment
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 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
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—> risk-taking, competition for mates and status Father's: slower strategy Marked by decrease in testosterone with entrance into committed relationship and with the birth of child
What makes a face attractive?
Age Symmetry—long term health, developmental stability Bilateral symmetry indicates long term health, developmental stability. Some mutations or imperfections in genes are reflected in face and affects symmetry. Consistent color—current health Make-up increases both perceived symmetry and health
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
Cultures of honor—examples
American south "Code of the streets"—inner-city street culture Herding cultures (more so than farming) Frontier areas (e.g. the American West)
Variance in men's reproduction
Because males are limited by access to mates, and females do not have to mate with different men, men's reproductive success is more variable Males' reproductive success is more variable. Women can mate with one man. When look at number of children, it's fairly equal among females. Pretty normal curve. When look at men, there is so much more variation. Some men can have 23 children. Here could be fewer men having 5 children.
Paternal investment
Bi-parental investment (social monogamy) in humans Males form long-term bonds with females, know who their offspring are (usually)
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.
Grand parenting
Biases in investment of second-degree relatives based on paternity uncertainty Paternal grandparents have lower paternity certainty
Asymmetries in parental investment
Females: egg: large (relatively) and limited in number Gestation Lactation Other costs Males: Sperm: cheap energetically and plentiful
Female preferences for investment
Financial prospects rated more important by women than by men in 37 cultures (Buss, 1987)
Humans are social animals. Why?
For this, it helps to look at why our primate relatives are social animals as well.
Weston, Friday, and Lio (2007)
Biometric evidence that sexual selection has shaped the hominin face What constitutes evidence for sexual selection? Sexual selection builds adaptations that help gets mate. Two primary forms of sexual selection (intrasexual/intersexual selection) Intersexual is like the peacock trying to get women. Intrasexual is like the gorilla having bigger teeth. Products of sexual selection: secondary sexual characteristics like differences in size, beards, etc. most of the evidence points to excluding same sex from access to the opposite sex—> same sex competition (intrasexual competition)—> have large teeth, muscle mass, etc. Evidence for sexual selection Presence of sex differences in the trait Across human populations Across species? Direct or indirect evidence for differential fertility or mortality associated with the trait Proxies: attractiveness or dominance judgements, mating success, status, health Trait is associated with testosterone in males Timing of trait development coincides temporally (in time) with mating competition —> looking at species with mating season—> see development of a trait that develops right before the breeding season (evidence that it's used for breeding); in humans, that's puberty—> when humans start thinking about mating Example: voice pitch Presence of sex differences in the trait Across human populations (yes) Across species (yes) Direct or indirect evidence for differential fertility or mortality associated with the trait (yes) Proxies: attractiveness or dominance judgements, health Trait is associated with testosterone in males (yes) Timing of trait development coincides temporally with mating competition (yes)
Foraging variance and sharing
Cashdan (1989): differences in cooperative food sharing norms among different bands of hunter-gatherers are linked to the amount of variance in foraging return rate !Kung San vs //Gana San Differences in cooperative food sharing in regards to different food items High variance food: meat Even with great effort, hunters often come home empty handed You can only eat so much meat before it goes bad Therefore, meat is shared widely among the group Low variance food: many gathered foods If gatherers come back without food, it's probably due to low effort Therefore, gathered food is typically shared among the immediate family (kin)
Sexual Selection
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. 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
Slow life history strategy
Characteristics: Larger body size Later reproductive maturity and first birth Few offspring High parental investment Low offspring mortality Longer lifespan
Fast life history strategy
Characteristics: Small body size Early reproductive maturity Many offspring Little parental investment High offspring mortality Short lifespan
Why isn't warfare more common across species?
Chimpanzees are the only other mammals Chimps engage in warfare This is very uncommon, but they do it Males get together with other males and patrol territory with their groups. When another male who isn't part of group tries to get into territory, they kill him. They are banding together, forming coalitions, and keep other males out. Anthropologists can clearly draw borders of chimpanzees' territories. Chimpanzee warfare is clearly instrumental (for a goal). It leads to annexation of territory—> more resources Defection and free-riding are important risks. As in the prisoner's dilemma, the problem of defection must be "solved." Ex: Turkana You're always vulnerable when you're cooperating, that's why there aren't more species who do it. 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 resources sanctions 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
MHC preferences
Choose individuals that are more dissimilar in MHC alleles Mate choice unique to the chooser Choose individuals that are heterozygote over homozygotes Mate choice agreement across choosers
Latitude—> sun exposure
Close to the equator=more ultraviolet (UV) radiation from the sun
Cultures of honor—southern men
Cohen et al. (1996): experimental studies of cultures of honor Conducted experiments in which the participant was insulted either in the presence of others or in absence of others (i.e. they were physically pushed while being called an "*******"). Southern (vs Northern) men were more likely to: Believe that the insult damaged their reputation Feel more upset by the incident (greater increase in cortisol, greater emotional response) Become primed for future aggression (violent completions of a mate competition vignette) Higher rise in testosterone Behaved in domineering ways Behaved in physically aggressive ways in a challenge situation
Ecological mismatch
Consequences of sleep disruption We sleep less Greater number of sleep difficulties Health deficits due to sleep deficits Human migration patterns and local adaptation
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
Foraging variance and sharing
Cross-cultural differences in the amount of cooperative sharing Ex: !Kung San vs //Gana San
Pathogen prevalence and mating
Cultural differences in the importance attached to physical attractiveness Gangestad and Buss (1993) Pathogens degrade physical appearance Therefore, people may adjust their mate preferences (i.e. importance placed on physical attractiveness) in response to pathogen prevalence If you had to rank everything you wanted in a mate, they find that people who live in high pathogen prevalence environments tend to rank attractiveness very high In Sweden, everyone is physically attractive. That's why people don't care about physical attractiveness
How does human nature affect culture?
Culture as a facultative response: "Evoked" vs transmitted culture Evoked culture (Tooby and Cosmides 1992) Phenomena that are triggered in some groups more than in others because of differing environmental conditions
How does human nature affect culture?
Culture as a facultative response: Evoked vs transmitted culture Evoked culture (Tooby and Cosmides, 1992) Phenomena that are triggered in some groups more than in others because of evolved responses to different environmental conditions/inputs
Cultures of honor: summary
Culture of retaliation may be evoked in response to a particular social environment (i.e. no rule of law, wealth can be easily stolen).
Production-Consumption: females
Deficit until age 45 Surplus during post-reproductive years Women are able to be at a deficit because they have males bringing food
In the EEA, it would have been adaptive to:
Desire foods in high 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.
Detecting kinship
Detecting kinship is a difficult problem How do people know their kin? Many potential inputs: Who does your mother care for? (MPA) Duration of childhood co-residence? Who does your father care for? Other childhood behaviors? (Co-sleeping, meals, play?) Phenotype matching? MHC complex? Facial similarity? What people tell you?
Mismatch
Diet/flavor mismatch Activity mismatch Ecological mismatch (sun)light exposure Pathogen exposure Reward mismatch Social mismatch
Evidence for sexual selection
Direct or indirect evidence for differential fertility or mortality associated with the trait Meta-analysis of research on fWHR showed: Higher fWHR is rated as less attractive Higher fWHR is rated as more threatening, and is associated with greater threat/dominance-type behaviors
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
Frequency-dependent selection
Frequency-dependent selection
Dominance hierarchies
Dominance hierarchies emerge from social competition for zero-sum, contested resources (food, mates, territory) Preferential feeding and mating access—> higher fitness How are dominance hierarchies "constructed" (and how are they studied)? They emerge from competitive encounters between individuals, and are a property of groups An individual defeats another individual when trying to get food—> next time, the defeated individual will not spend time fighting with other individual for food and just lets that individual get food. Then a social rank ladder type thing comes out. Transitive/linear: if A defeats B and B defeats C, A is automatically dominant to C Positional: rank is relative Rank shifts over time
Secondary cue: co-residence
Duration of childhood co-residence Westermarck hypothesis Prediction: they onger you co-resided with another individual during childhood, the more likely you are to encode that individual as a relative When hunger-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-gatherers/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.
Hunter-gatherer "massacre;" 10KYA
Evidence of 27 individuals who met violent deaths Have clubbing deaths, etc. evidence that many individuals' hands were tied behind their back. Clearly there was one aggressor that won. It's aggression from one group towards another group—> can put it in heading of warfare in small scale societies.
Which cues does kin detection system evolve to take as input?
Evidence so far... Maternal perinatal association? (Yes) Duration of childhood coresidence? (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 Males: guard against partner's sexual engagement
Cooperative coalitions
Examples: Large game hunting (ex: people have two boats on either side of boat and attack whale with spears) Food sharing Building shelters Launching a raid on another group (warfare) Defending against attacks from another group (warfare)
Are humans monogamous?
Extra-pair mating + defacto polygyny + sexual dimorphism: suggests a history of mild polygyny in humans However... paternal investment is an important feature of the human mating system
Are humans monogamous?
Extra-pair mating + defacto polygyny + sexual dimorphism: suggests a history of mild polygyny in humans However...paternal investment is an important feature of the human mating system
Measures
Facial width-to-height ratio Three other ratios known to be sexually dimorphic All incorporate dimensions of the lower face/jaw Looked at trait in age, testosterone, strength. Strong and significant relationship with age, testosterone and strength when it comes to the chin trait. With fWHR, there is no correlation.
Role of culture: EP
False dichotomy between biology and culture EP: culture is both the independent and the dependent variable Human nature affects human behavior and influences culture SSSM only looks at how culture affects human behavior
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
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 they're investing in is their own The primary reason why paternal investment is so rare across species
Good genes
Genes that confer better parasite and pathogen resistance Indications of good genes/health: Visual cues: facial attractiveness Age Symmetry Consistent color High carotenoids content Sexual dimorphism Smell (MHC) Beauty is in the mind of the beholder
Good genes
Genes that confer better parasite and pathogen resistance Indications of good genes/health: Visual cues: facial attractiveness Age Symmetry Consistent color High carotenoids content Sexual dimorphism Smell (MHC)
Gini and homicides
Gini: measure of income and inequality Gini index (indexes income and equality) is clearly related to the rate of homicides in a community. More income, more levels of homicide
The present research
Goals: Is fWHR sexually dimorphic? If so, when do sex differences emerge? And is fWHR associated with pubertal testosterone? If not, why not? Two samples North American individuals, 3D scans, Ages 3 - 40 Bolivian Tsimane individuals, 2D photos, Ages 7-21 3D sample: 3D facial norms database 2,450 unrelated individuals of European-Caucasian ancestry Males and females, ages 3-40 (roughly equal N in age and sex categories)
Very controversial research
Men have something to gain in their raiding People didn't like to think that there is good from raiding Even showing that warfare has decreased in the modern world. People thought that he was trying to say that we don't need to diminish warfare because everything is peachy right now. That's not what he was trying to say. Naturalistic fallacy.
What makes a face attractive?
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 (testosterone is a handicap because negatively affects immune system—>like peacock's tail) Female sex hormones (e.g. estrogen) are associated with age and fertility
Environmental heterogeneity in fitness optima
Heterogeneity: the state of being heterogenous. 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 Human migration 100-10kya Selection can favor different levels of a personality trait in different environments Ex: the &R (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 Higher historically migratory populations than sedentary populations Higher in populations that migrated farther (in miles; 1,000-30,000kya). This could be an issue of mismatch; this hyperactivity was good for moving around in environment and learning through exploration. Now leads to behavioral difficulties in people who have this allele in modern environments—> sitting still at a desk in a classroom all day
MHC heterozygotes and attractiveness
Heterozygotes were rated as more attractive than homozygotes Attractiveness as a proxy for health
Overgeneralization of emotion
High fWHR bears some resemblance to the anger face Draw down the brows, which makes face look wider. When parse lips, make the bottom part of face narrower. So emotion makes faces look wider perhaps High fWHR are more accurately recognized as angry and and low fWHR are more accurately recognized as fearful and happy
Female dominance hierarchies
Higher rank leads to higher reproductive success in females too For females, status translates into reproductive success We inherited from primates this general system for seeking status Inherited it because higher status led to higher reproductive success both for females and males
Dominance hierarchies
How can we study dominance hierarchies in non-human primates? Observe deference behavior (deference behavior=lower status being shown; making yourself smaller and lower)
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
Timing of trait development coincides temporally with mating competition?
Human puberty Mating competition sharply increases in humans Facilitated by a drastic increase of testosterone in males
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 Skin color Political affiliation Speech Dress Food choice/prohibitions, and more...
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 Polygyny: multimale (like chimpanzees) We look a lot like Pair bonded species because we have emotional attachments and we raise kids together.
How are humans different from other primates?
Humans form long-term pair bonds Men's reproductive rate is slowed by bonding to one human Humans are different in another way: prestige. Humans can attain status not necessarily by their strength, but by their unique skills that they have to people. Like Stephen Hawking on a stage: people giving him status because they want to learn from him
FWHR and testosterone
If fWHR is a product of intersexual selection, and testosterone (T) coordinates male phenotypes for mating competition, fWHR should be associated wit hT. Meta-analysis of adult T and fWHR: No relationship
Carre and McCormick (2008)
If fWHR is sexually dimorphic, then it may be the product of intersexual selection (i.e. male-male competition) If a product of intersexual selection, fWHR should be correlated with other .... Looked in varsity and professional hockey players to see if this ratio is correlated with aggression; found out that men with wider faces spent more time in the penalty box. Asked these hockey players about their aggressiveness—> guys with wider faces had more aggressive behavior
What is 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 these 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???
Production-Consumption: males
In foraging populations, men produce more than they consume After 5, consumption and production are the same Every piece of food the chimp eats they produce For humans, at 18 the people are eating way more than they were producing. After that, they produce way more than they eat—> goes towards children
Social mismatch
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 People underestimate the common risks, like car crashes because they see stuff on the news or in real life all the time
Ecological mismatch
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 —> people descended from africa have much higher deficiency than white people. Because dark melanin blocks sun Low vitamin D related to a number of physical and psychiatric conditions, including depression and fatigue
Men's preferences for physiological investment
Men place greater emphasis on physical characteristics in mates across 37 cultures Men's preferences for hip and thigh fat Prefer a waist to be smaller than the hip Then found that if had more fat on hips and thighs, women were more preferred Comic book characters—> tiny waists that are impossible for real life women to have This is supernormal stimuli—> still elicits a response from men Like jewel beetle mating with beer bottle —> shows that natural selection created these programs that are used to select for certain traits
In-group favoritism and out-group derogation
In-group favoritism: the tendency to favor people we regard as members of our own groups 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, ouitropus 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 out-group as all being identical Out-group derogation
What forces have acted on humans?
Intrasexual selection/same-sex competition Intersexual selection/opposite-sex choice Men commit nearly all same-sex homicides. Intra vs intersexual selection? Look at how it affects attractiveness vs how it affects dominance (strength) Looked at full beard vs clean shaven, masculine vs feminine voice, masculine vs feminine male face, brawny vs typical male build—>all these things affected dominance instead of attractiveness. One source of evidence that intrasexual selection had more effect on males
Evidence in support of westermarck
Israeli kibbutzim: Children were reared, from an 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 Kind of like a communal living type thing 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 relations 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" 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
Examples of human parental investment across cultures
Men take care of sister's kids becuase know sister is related, but dont know if own kids are related
Costs of being social
Larger groups more visible to predators Larger groups need more food, so more competition for food Increased competition for mates
The architecture of human kin detection
Lieberman, Tooby, and Cosmides (2006) Facultative regulation of heavier based on kinship Coresidence duration monitoring circuitry, maternal perinatal association monitoring circuitry, additional cue monitoring circuitry—> kinship estimator—> programs regulating sexual attraction, programs regulating altruistic behavior Predictions: Older siblings detecting younger siblings: MPA, not co-residence Younger siblings detecting older siblings: MPA unavailable, co-residence most important Survey measures of sib-directed altruism and sibling incest aversion Altruism toward particular sibling: How many favors did you do for this sibling in the last month? (Behavioral) Would you donate a kidney to this sibling? (Attitudinal) Sexual aversion: Degree of disgust at prospect of sexual contact with a specific sibling (passionate kissing, sex). Rank and Likert measures Moral opposition to incest Results show that when MPA is absent, individuals use coresidence duration as a cue to kinship
Homicide rate and male life expectancy
Life expectancy is homicide-independent! This one variable explains ¾ of the variation in homicide rates. Higher mortality—> faster life history strategy
Chromosomes come in pairs
Locus: place on the chromosome where alleles are found (like an address)
MHC
MHC=Major HIstocompatibility Complex Genes that impact the immune system Parasites and pathogens are an important selection pressure in human evolutionary history These genes are incredibly important; part of immune system and attacks parasites and pathogens 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 Totally identical at 2/3rds of genome, but people are super duper different at this location of the genome. This diversity was obviously important; adaptive value in having a different allele than someone else. Running as fast as you can to stay in the same place; favored people with different immune system because able to reproduce with people that have more tools to fight off parasites and pathogens. Being a heterozygote is good for survival and reproduction Among HIV-infected humans, heterozygote had better survival In a study of humans, MHC-dissimilar mates had greater fertility (if dissimilar more likely to produce heterozygote with different MHC alleles; have more diversity and more likeliness of surviving) 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.
Maternal perinatal association (MPA)
MPA: observing your biological mother caring for a neonate. Only works for older siblings detecting younger siblings. Younger siblings can't use older sibling MPA. Evolved system defaults to a different input/cue.
Sex differences in desired sexual partners
Males desire a greater amount of sexual partners than women Conforms to basic mammalian prediction that males want more sexual partners How many sexual partners do men and women actually have? More men have more partners
Benefits of being social
Mates usually easy to find More individuals to look for food More individuals to defend food Better defense against predators
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 Latitude—> sun exposure—> melanin—> vitamin D and folate South America has more densely forested areas, whereas in Africa there are more deserts and savannahs—> more exposure to sun even though in equator Migration has the most effect on this. Humans evolved in Africa. In africa, have long history of adapting to africa. In South America, they're descendants of people that had lighter skin to begin with, and they've been in that area for not very long. Haven't had as much time to build up a darker skin color.
Jealousy studies
Men and women asked to picture themselves in a serious, committed romantic relationship They were presented with two alternative scenarios: Their partner forming a deep emotional attachment to someone else Their partner having sexual intercourse with someone else Men found sexual infidelity more threatening than emotional infidelity and the opposite for women
Intrasexual selection
Men are larger, more muscular, and more aggressive This suggests a history of intrasexual competition over access to women.
Is fWHR actually sexually dimorphic?
Meta-analysis (Geniole et al., 2015) showed small effect of sex (d=.11; small effect Not across species Direct or indirect evidence for differential fertility or mortality associated with the trait (are people with wider faces living longer?) Forensic sample 523 males, 339 females Narrow-faced males are more likely to die from contact violence Stimuli sets of male faces, have moderate effect size Looked at fWHR in actual faces and extent to which it is subject to violence and dominance behavior Found that males with broader faces have cheated more in economic games, more broader faced males are CEO's Males with broader faces are also strongly perceived by others as more aggressive (effective size r=.46) This trait is actually seen as unattractive If it is a product of selection, not a product of female choice; must be male-male competition
But...what is going on here?
Meta-analysis of research on fWHR showed: Higher fWHR is rated as less attractive Higher fWHR is rated as more threatening, and is associated with greater threat/dominance-type behaviors in men
Ovulation and women's mate preferences
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
Major themes
Natural selection is a powerful framework for understanding our world and for generating testable hypotheses. Learn to ask WHY! Proximate vs. ultimate distinction The following dichotomies are false: nature vs. nurture, biology vs. culture, genes vs. environment, innate vs. learned The influence of natural selection on our brains does not imply a fixed destiny Most (interesting) adaptations are facultative, and calibrated during development
Cultures of honor
Nisbett and Cohen describe the "cultures of honor;" Having a reputation for strength and toughness is treated as extremely important Individuals are prepared to protect their reputation (i.e. gain respect) with violence Governed by the "rule of retaliation" Proverb in North Carolina: every man "should be a sheriff on his own hearth" Those who are wronged must exact revenge themselves to restore their honor These cultures are likely to develop where A man's resource holdings can be stolen in full Ex: herds of animals, drugs The governing body is weak or nonexistent thus cannot prevent or punish theft
Life history strategies
Stanley Burrell (aka MC Hammer) Peak: earning 33 million/year (1991) What he spent it on: Entourage of 200 (costing 500K/moth) Mansion (gold-plated gates, etc.) 21 racehorses And much, much, more... Bankrupt by 1996 78% of former NFL players have gone bankrupt ⅓ of lottery winners go bankrupt Two general life history strategies across species: Fast life history (aka r-selected, when referring to species) Slow life history (aka K-selected) Think of r- and K- selected species as ends of a continuum
Differences between now and the EEA
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 Fruit is an attraction for organisms to eat the fruit and spread of that plan Goff and 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" No flavorings mimic plant secondary compounds No Doritos in the EEA Mismatch between flavor and nutrition: in the EEA, flavor and nutrient were effectively the same thing. A huge difference between now and then is that ancestors would have been healthier acts a result. No supermarkets,s to take out, no Cuisinarts Allfood 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?
Differences between now and the EEA
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
3D sample
No evidence of sex differences in any of the age categories Significant decrease in fWHR during development Also huge amount of variance in this trait in adult sample (age 22-40). No sex differences. When looked at all ages combined, significant negative association—> face getting narrower Multiple regression predicting fWHR with sex, age, and BMI No sex difference for any of the age categories.
Difference 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.
Differences between now and the EEA
No fat and sugar dense foods Leaner game meat (with high omega-3 fats) vs.domesticated CAFO animals bred for high fat content. No modern food creations Foo hydrogenated, trans fats Not additives, stabilizer, and other chemicals No refined goods (so there was always a lot of fiber, and high nutrient density
Hypotheses
North American individuals, 3D, ages 3-40 Child group: 3-6 Juvenile group: 7-11 Adolescent-to-young-adult group: 12 - 21 Adult sample, 22-40 If fWHR is a secondary sexual characteristic shaped by sexual selection, the sexual dimorphism should be absent prior to puberty (childhood and juvenility), increasing during adolescence, and present in adulthood.
Ecological mismatch
Novel ecology Light regulates our circadian rhythms Relative presence of blue light indicates the day/night We are diurnal species (asleep during night awake during day) Light exposure and sleep Exposure to blue light at night disrupts sleep patterns Consequences of sleep disruption We sleep less Greater number of sleep difficulties Health deficits due to sleep deficits
Fast life history strategy
Often found in environments with high extrinsic mortality (e.g. predation) rates Why? Long-lived individuals were selected against; those that reproduced quickly passed more genes to the next generation In rats and mice, it doesn't pay to invest in long life because they are preyed upon. Have very high mortality
Slow life history strategy
Often found in environments with low extrinsic mortality (e.g. predation) rates Why? 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
Individual differences
On which dimensions do we vary? Every dimension! Personality refers to the ways we differ psychologically
Fast vs. slow life history strategies in humans?
Stanley Burrell (aka MC Hammer) Grew up extremely poor, many many siblings in a one-room apartment Grew up with less expectation for future
Kin selection
One of two explanations for apparent altruism (the other is reciprocal altruism) Altruism: taking a cost to benefit another individual
Having children decreases men's testosterone
One study examined changes in testosterone (T) over time in the same individuals Groups are categorized by change in fatherhood status
Personality
Openness to experience: curious broad interests, creative Conscientiousness: organized, reliable, hard-working Extraversioin: 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 (might not be a species specific thing. So maybe modern humans are different?)
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 et al: people (mis)read skin color as a badge of coalitional membership/alliance
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 and 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
Parental investment and monogamy
Paternal investment and monogamy slow men's maximal reproductive rate down Are humans monogamous? Two main sources of potential information: Comparison of human mating with close primate relatives Analysis of human sexual dimorphism Plus, several other clues
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
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—> women mate with many men. Any woman that mates with different men will tell men which child is theirs. Men think that each child is a little bit his own. In this species, have very low paternity certainty. Particle paternity
Status is positional in humans
People strive for relative status, not absolute wealth, dominance, or prestige Arms race for positional goods Two options: You live in a 4000 square foot house and others will live in a 6000 house You live in a 3000 square foot house and others will live in a 2000 square foot house People want to have a bigger house than everyone else Choice is switched for vacation time (non-positional good) You get 4 days of vacation and others will get 6 days You get 3 days of vacation and others will get 2 days Seems like you should choose the 4 days even though you will have less days than someone else, but people care about relative status—> want more than everyone else. Even though less than absolute. 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
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 Nonpositional goods: 401K, savings account, vacation time These goods show how capable you are of things People try to strive for relative status, not how much wealth they have or how many birds they have seen, but how much they have in comparison to other people. Have I seen more birds than you?
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 engages Social comparison and impossible ideals Celebrities as pseudo-neighbors People see other people posting happy things on facebook and feel like there's more competition
Benefits of status inhumans
Status and reproductive success in 33 non-industrial societies Looked at polygynous and monogamous societies Dark line on graph=higher than chance Total fertility, mating success, infant mortality, etc. basically higher status led to higher reproductive success
Heritability
Personality and intelligence (and other measures of psychological variability) have moderate heritabilities (0.35<h2<0.65). What does that mean? Usually misunderstood by journalists 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: They have different genes They have different experiences Heritability is a method to "partition" the differences 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 Vp=Vg+Ve Phenotypic variation in a population (Vp) is the sum of the underlying genetic variation (Vg) plus the effects of different environments (Ve) on the expression of those genes And so, if we want to know how heritable a trait is, h2=Vg/Vp, thus h2=Vg/(Vg+Ve) and h2 varies from 0 to 1. Heritability is low when Vg is low and/or Ve is high. (Eye number, language) Heritability is high when Vg is high and/or Ve is low. (Blood type, height) Heritability of the same trait can vary depending on the environment Having two eyes or five fingers has 0 heritability. Heritability is not whether or not something is hereditary. Heritability is a proportion Heritability of height is around 0.8 (this is among the United States). In sub Saharan Africa, the heritability of height is 0.5 because of the environment. There is a lot of variability in sub Saharan Africa (Ve is bigger in sub Saharan Africa) because there is more environment variability. More people starving there. Many psychological traits have significant heritability You personality cannot be 60% of genes or environment. They are trying to compare people, so one person can have more genetics that control personality than someone else
Evoked culture
Phenomena that are triggered in some groups more than in others because of differing environmental conditions !Kung San: sharing norms triggered by food variability
Why is there variation in these traits?
Potential reasons: Facultative traits Life history trade-offs Selectively neutral Sexually produced variation around polygenic optimum Spatial or temporal variation in selective regime Frequency-dependent selection Environment heterogeneity in fitness optima
Evidence for sexual selection in fWHR
Presence of sex differences in the trait Across human populations Meta-analysis of 2D photos and 3D scans: small effect size Meta-analysis of skulls: small effect, only in East Asians Present study: no sex differences Across species: Sex differences in fWHR among Capuchin monkeys (but mediated by sex differences in body weight) and chimpanzees Can sexual selection have occurred if there are no sex differences?
Detecting kinship
Problem: how do people know their kin? Solving this problem is important Kin selection: who should receive altruistic behavior ALSO: incest avoidance: who shouldn't you mate with?
Biometric evidence that sexual selection has shaped the hominin face
Proposed a new criterion to sex human crania: facial width-to-height ratio 68 males and 53 female H. sapiens Native southern Africa population
What is evolutionary medicine?
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
Why is this important?
Remember gorilla example Harems (one male, many females)--> male mates with all females and has a ton of babies Males potentially have more to gain by mating with more mates
Examples of evoked culture
Review Paternity certainty and matrilineal inheritance Social inequality and violence Foraging variance and sharing Pathogen prevalence and mating preferences Cultures of honor
FWHR measure
Right Tragion (t_r): point marking the notch at the superior margin of the Targums, where the cartilage meets the skin of the face Etc
Status
Status: the position or rank of an individual (or group) within a society Authority, cachet, dignity, dominance, esteem, face, position, etc People treat status as very important
!Kung San
Strong economic and political egalitarianism Strong sanctions that reinforce food sharing and discourage hoarding Calling someone "stingy" is a great insult Displays of arrogance and authority are also discouraged "The proper behavior or a !Kung hunter who has made a big kill is to speak of it in passing and in a depreciating manner...; if an individual does not minimize or speak lightly of his own accomplishments, his friends and relatives will not hesitate to do it for him." (Cashdan, 1980)
Role of culture: SSSM
SSSM (standard social science model): Culture is the independent (causative) variable Culture—> behavior But where did culture come from? Why don't other animals have culture? Do they? Why is human culture so constrained? Why are there so many universals?
DHA (one omega 3 fat) builds healthy brains
Saw that countries with higher omega 3's in breast milk scored higher on math tests In another study looked at hip and thigh fat and cognitive scores of offsprings. Found smaller hip and thigh ratio correlated with higher cognitive scores
Red queen model for sexual reproduction
Sex appears to be a counter-strategy to parasites and pathogens Creation of unique genotype for each offspring Hence "good genes" are the ones that confer parasite and pathogen resistance
Sexual dimorphism
Sexual dimorphism reveals the degree of polygyny in a species E.g. gibbons vs. gorillas Gibbons look identical, but there is high sexual dimorphism in gorillas
First, why have sex at all?
Sexual reproduction is costly Only half your genes passed on Disrupting successful genotypes is costly Mating is costly Time, energy, danger
//Gana San
Show considerable economic inequality: More hoarding, and food is rarely shared outside of the extended family More polygynous (some have many wives, others have none at all) Wealthy, high-status men are quick to claim that they speak for others
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 Childbearing starts after adolescence Relatively few possessions, mostly egalitarian No way to know about the world beyond the people you talk to. No media exposure. Human brains predicts larger group size 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
FWHR, perceptions, and behavior
Summary of meta-analysis: Strong effect of fWHR on perceptions of threat, dominance, and masculinity in men's faces Moderate effect of fWHR on actual dominance behavior and sports performance Why? Must be from testosterone
How to detect MHC?
T-shirt studies Men and women wear a clean t-shirt for two nights. Rafters 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 more divergent
Westermarck and childhood coresidence
Taiwanese sim-pua marriages (aka minor marriage) Baby girl adopted into future husband's household, raised with him (ended in the 1970's approximately) The later the girl was adopted to the family, the more children they had (we can guess they had less sex if the girl was younger because they were less sexually attracted) Probability of divorce were much higher when the girls were adopted into the family at a younger age.
Our intellectual baggage
The "debate over human nature:" Hobbes vs. Rousseau Hobbes: "nasty, brutish, and short" Rousseau: man is essentially "good" We feel like we need to choose if people or good or bad. One or the other. Evolutionary psychology just wants to know how something evolved and how it led to reproductive success and as a result more popular in a population.
Naturalistic fallacy
The error in logic that what is "natural" (i.e. evolved by natural selection) is "good" (i.e. in a moral or ethical sense). Naturalistic fallacy was the basis of "social darwinism" / eugenicists Equality of rights and opportunities cannot be contingent on equality of traits (e.g. temperament, personality, behavior, etc.)
The evolution of sexual reproduction
The red queen hypothesis: sexual reproduction helps organisms evade fast-breeding (and, therefore, fast evolving) parasites Evolve very fast to beat parasites Faster generations Example: snails (p. Antipodarum) population with both sexual and asexual reproducers Long-term study showed that as parasitism increased, asexual reproducers died off (no genetic variation in a lineage—> once parasite evolved a way to beat snail, it was able to since the genes were the exact same as the parents)
Inbreed depression
There is a 50% chance your sibling also carries the harmful mutation If you mated with a sibling, the probability that your children would have the disease would be 12.5%
Variation in violence
This perspective suggests that risky competition (violence) is a facultative response Those who anticipate short lives, have minimal access to resources, and observe that they are lowest on the social hierarchy may be more motivated to employ drastic measures to try to change their life course
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
Why do men care about 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? 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 Humans differ from other primates in body fat. Primates don't really have hip and thigh fat No sexual dimorphism in hip and thigh fat This is not the case in humans: reproductive-aged women deposit fat in their hips thighs and butt. Women have higher body fat percentage than men Dr. Gaulin's argument: Menarche (age at first menstruation) depends on fat distribution, not total fat. Greater hip and thigh fat is associated with earlier menarche. Indicates that the body is ready to conceive Each successive offspring depletes hip and thigh fat (relative to upper body fat). Hip and thigh fat is some sort of resource that the body draws upon when has children. Hip/thigh fat and abdominal fat have opposite effects on the supply of two LCPUFA's (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!
Incest avoidance
Why is mating with siblings bad for reproductive success? 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. Children of incest have a higher chance of congenital diseases and deformities
Two types of nature/nurture questions
Why is my tan this color? What are the causes of development? Genes AND environment: interaction between genes and environment that has been pre-programmed by natural selection Ex: calluses, tanning Why do people differ in how tan they are? What are the causes of variation? Cake analogy
Cultural variation in violence
Why might social inequality be rated to violence? People value their relative (not absolute) amount of resources because social status is inherently relative What are the consequences of winning and losing social/status conflicts for those who have the most vs. the least?
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
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
Men's preference for physiological investment: age
Women's fertility declines with age With unprotected sex, there's a 25% chance (at age 22) of getting pregnant during ovulation period. Goes down after that. Women are limited to number of years of fertility Late 30's, early 40's, chance of fecundity declines sharply Men's preference 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 wives
Observed patterns of human parental investment across cultures
Women: invest in their own children In no society do women take care of their sister's children but not their own. In no society do women take care of their brother's children but not their own. Men: invest in their own children Some societies, men invest in their sister's children but not their own. Like father-uncles. In no society do men take care of their brother's kids but not their own If paternity confidence is strong, that's 0.5, but if less confidence, lowers that number Women could be unsure about sister's children in low paternity confidence because her mother could have mated with a different father (sister could be half sister) For men, when there's high paternal confidence, they take care of their own children, and when low paternal confidence, take care of their sister's children
Are humans monogamous?
Yes? Humans form long-term pair 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 reported having at least one affair Divorce and remarriage: defacto polygyny (men are more likely to remarry). Intermediate testes size (suggests that there is competition for access to the egg). Intermediate testes size (larger testes size is selected for) means polygyny. not perfect monogamy during evolutionary history. females not always mating within pair bonds.
