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Chapter 2

Ch. 2 notes - Evolution.docx

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Christopher Teeter

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Chapter 2 – Evolutionary Psychology *note: NS = natural selection Section 1: Introduction • Evolutionary Psychology – the pursuit of psychological science with explicit attention to contemporary knowledge and theory about the evolutionary process – scientists approach the study of the mind and behaviour as a branch/subfield of evolutionary biology • Biology – science of life – encompasses everything that distinguished living things form inanimate ones • The theory of evolution is the unifying conceptual framework of biology • Study by Claus Wedekind: males were odour donors and females rated the odour for intensity and pleasantness • Used molecular genetic techniques to determine the students’ genotypes with respect to 3 particular genetic loci – members of the Human Leukocyte Antigen (HLA) group/Major Histocompatibility Complex (MHC) (2 names for the same thing) • These genes play a role in immune function and are known to affect body odour in mice and other mammals • The shirts had been worn by men who were either genetically similar/different to the rater in their MHC profiles • For the purpose of analysis, women were divided into 2 groups: on oral contraceptives/natural cycle • Naturally cycling women rated odours of genetically dissimilar men as significantly more pleasant than those who were similar/women taking the pill showed the opposite – more pleasant for those who were genetically similar • The hypotheses for this exp. were derived from ideas about the evolved functions (“purposes”) of women’s reaction to male odours 1. A woman’s choice of mate can be influenced by her affective responses to male odours 2. Potential cost associated with being attracted to people whose MHC genes are similar to yours – couples with similar MHC genotypes have an inc. likelihood of producing offspring with less versatile and weaker immune systems - NS Should favour preferences for partners who are dissimilar in their genetic makeup 3. Taking oral contraceptives puts women in an infertile psychophysiological state in which their affiliate preferences no longer reflect and evolved “strategy” for screening potential mates – instead function in the realm of social support  Male odour was collected and rated by females because females tend to be more discriminating in mate choice than males – bad choices are more costly to females – must make a major investment in each successful offspring • Experimental psychologists without an evolutionary perspective are also trying to discover previously unknown causal influences on physiological responses (what Wedekind was looking at) • Discoveries:  self-similarity at certain genetic loci affects women’s responses to male body odours  women’s hormonal state exerts a modulating effect on these affective responses • no psychologist operating without the heuristic benefit of evolutionary theories and knowledge could ever have discovered these facts Section 2: Essential Facts and Ideas about Evolution The Concept of Evolution • populations of organisms evolve over generations • one line of evidence: fossil record of extinct plants and animals • another line of evidence: both contemporary and extinct organisms can be readily and non-arbitrarily situated on a branching “tree” on the basis of: • similarity – interpretable as phylogeny – a pattern of divergence of distinct evolving lineages from common ancestors • similarities in early development (ex. anatomical similarities of embryos of different species prior to birth) • similarities in DNA sequences incl. sequences of non-transcribed “neutral” DNA • when independently constructed phylogenies are compared, they tend to be almost identical • usually evolution is a slow process but can occur within the lifetime of an individual scientist • In rapidly-producing microorganisms, it can happen even faster – significant evolutionary changes can arise and sweep through pop. in less than a year – ex. disease organism rapidly evolves resistance to a previously effective antibiotic • Darwin’s finches – seed-eating birds changed beak size and shape as Darwin studied them • Few animals went to the Galapagos Islands – one was the ancestor of the Darwin finches – they underwent “adaptive radiation” to fill all the ecological niches not ordinarily available to finches (ex. Woodpecker finch and Vampire finch which eats blood from seals and other large animals) • Peter and Rosemary Grant also studied these finches – mid 1970s there was a bad drought on one of the islands, there were few small seeded plants remaining – witnessed beak changes in the finches – Natural selection: the ones who survived had bigger beaks to eat the bigger seeds and the ones with smaller beaks died off – found that beak size was a heritable trait The Theory of Evolution by Natural Selection • Darwin called the process of animals evolving over generations “descent with modification” • Darwin had the theory of evolution worked out in the 1830s but he anticipated controversy and wanted to make an airtight case so he waited till 1858 to go public with his theory – provoked to publish by Alfred Russell Wallace (had similar ideas) • Individuals within a species differ and some of the ways they differ may affect their survival and reproduction • Offspring tend to resemble their parents in these variable attributes to some degree – parents and offspring are more alike on any quantifiable trait than 2 randomly selected individuals • Young are produced in excess – in any species more young are produced than will eventually become breeders in their turn/than would be necessary to maintain the pop. • Natural selection does not always cause change – if a pop. is well adapted to its ecological niche then NS may just be stabilizing: a process that eliminates harmful departures from the optimal species-characteristic design – prevents evolution • The circumstance that NS may be needed is when ecological demands change (like what the Grants documented with the Finches) Section 3: Why Evolutionary Theory Matters to Psychological Design Adaptations • Waterflea (Daphnia magna) – tiny crustacean that is eaten by some fish – exhibits phototactic behaviour: when the sun is visible, it sinks lower in the water to avoid being seen by predators/when the sun is not visible it comes close to the surface to feed – more likely to behave phototactically when the water contains chemicals excreted by fish predators (threat of predation) • Study of the eggs of this flea show that this phototactic behaviour evolves as a function of the risk of predation • Offspring hatched from eggs that were laid when there were no fish in the pond responded less to light in the presence of fish chemical cues than the ones that hatched from eggs laid when there were fish in the pond • The fleas with genes that caused them to behave phototactically in the presence of fish predators were more likely to survive to lay eggs than the ones that did not display this behaviour • When there was no threat of predation, the fleas with genes that did not cause them to behave phototactically in the presence of fish predators were more likely to survive to lay eggs than the ones that displayed this behaviour • Evolutionary psychologists sometimes call themselves adaptationists • Adaptation: many traits of organisms (physical and psychological) serve specific functions that benefited their bearers over generations by inc. their reproductive success/fitness • Adaptationism – approach to investigating organismal design in light of the notion that many aspects of an organism’s phenotype (appearance and behaviour) are the direct and indirect productions of adaptations Functionality • Psychologists must infer putative adaptation form its outputs (how it operates under specific conditions) – cant “see” psychological adaptations like you can with physiological ones • Russell Jackson and Lawrence Cormack (2008) – hypothesized that humans possess psychological adaptations whose function is to protect them from falling from great heights – perceive the vertical distance between two points to be greater than it actually is – inc. as the viewer inc. in distance from the ground/moves to a higher position • Subjects made larger estimates of vertical distance when positioned at a higher point than a lower one – did not overestimate when looking at the distance horizontally, not matter the height they were above it • May help people avoid falls by inducing them to be more careful when moving around in high spaces • What’s missing from the adaptationism of non-evolutionary psychologists is selectionism • Psychological adaptations serve to inc. fitness: the relative reproduction of an individual’s genotype as a consequence of its traits • Organisms have mental traits/features/attributes because their ancestors who had the same traits reproduced more successfully than other individuals in the pop. with different traits • Does not mean that individuals know (consciously/unconsciously) that their psychological adaptations served this essential purpose in the past • Also does not mean adaptations continue to be reproductively advantageous in contemporary environments – world changes all the time and adaptations take a lot longer to change • Also does not mean psychological adaptation is perfect – just that it performed better (ex. more efficiently) than other traits for the same task Section 4: Mate Choice and Sexual Jealousy Sexual Selection • Special form of natural selection – specifically pertaining to finding a mate • Competition among individuals of one sex over access to the other sex (intrasexual selection) and competition to capture the interests of the other sex (intersexual selection) • Mate choice: the psychology underlying who to mate with • Females invest a lot more into offspring than males do (carry the child then care more for its basic needs) • Difference between optimal behaviour in the sexes: males benefit from attempting to reproduce more often than females – re-enter mating “pool” more often – males invest less in offspring – recently mated male can attempt to find a new mate and reproduce with her sooner than a recently mated female • Men tend to prefer younger women (reproductive age)/women tend to prefer wealthier, slightly older men – can invest in their offspring • Men desire greater numbers of sexual partners and are more willing to engage in casual sex than women • One function of a mate is to produce offspring – hypothesize that individuals look for someone that show cues of reproductive ability/fertility • Another function is to produce “high quality” offspring (best chance to survive and reproduce) – hypothesize that individuals prefer mates that present cues of “quality” as well, assuming quality of a parent is transmissible to their offspring Cues • Why would quality genes be transmissible? – some individuals bear genes that make them better adapted to the local environment – individuals should look for cues that a mate bears these locally adapted genes • Cues to fertility and quality: • Fluctuating asymmetry – measure of bilateral (left vs. right) traits that are symmetrical over the pop. as a whole but not necessarily for a particular individual – optimal body will tend to be symmetrical  Ex. more efficient to walk with 2 legs that are the same length  Over their lifespan, individuals will encounter hardships (ex. disease/injury) that will affect their development and they will become more asymmetrical – harder to maintain symmetry than it is to become inc. asymmetrical – individuals that are better adapted to the environment should be more resistant to these things and will develop more symmetrically than individuals who are less adapted • Health is related to fluctuating asymmetry – individuals more likely to succumb to disease will also tend to be more asymmetrical – one of the cues to health  Healthier individuals will make better choices for mates – might pass on the genes that keep them healthy to their offspring and they can stay around longer and in better condition to help rear and support offspring • How feminine/masculine an individual appears – consequence of differences in hormones that men and women have been exposed to over development – can affect qualities incl. fertility and physical strength and physical appearance related to the biological sex  ex. waist to hip ratio (circumference of waist divided by circumference of hips) – strongly sexual dimorphic – women tend to have narrower waists relative to their hips than men do – indicative of feminine/masculine characteristics – women with lower ratios are more fertile • these cues predict attractiveness – people find symmetrical faces to be more attractive and symmetry is associated with self-reports of personal health • women’s attractiveness preferences vary as a function of their stage in their menstrual cycle • cuckoldry – long-term mate is led to believe that another man’s children are his own • women are fertile during the ovulation phase – most concerned about certain qualities of physical attractiveness during this phase – stronger preferences for facial masculinity and short-term preferences shift towards being attracted to men who are more confident and talented – also prefer smell of symmetrical men based on a t-shirt that they wore (never saw the person) • More concerned with other benefits like the long-term investment potential of a mate during other phases of their cycle • Long-term preferences were relatively unchanged by menstrual cycle phase Infidelity • Until recently (technological advances) a fetus carried by a woman was guaranteed to be her own genetic offspring • Men cannot be certain of their paternity (until recent technological advances) – a woman could mate with any man incl. a different one than her long-term partner • Man’s fitness interest to invest in his own genetic offspring and not the offspring of another man – male psychology should have evolved to avoid being the victim of cuckoldry • Evolution-minded psychologists predict that male and female sexual psychology should differ in how the 2 sexes respond to infidelity • Men risk losing fitness when their mates have sexual relations with other men • Women risk losing fitness when their mates take resources out of the relationship and invest them in a relationship with another women • Men are more prone to sexual jealousy: feelings of anger and a desire to guard a mate/sexual prospect from engaging in sexual activity with potential rivals • Women more prone to romantic jealousy: feelings of anger and a desire to guard a mate/sexual prospect from leaving the relationship to form a new one with potential rivals • Study by Buss, Larson, Westen, and Semmelroth (1992): subjects presented with 2 scenarios and had to choose which would be worse: (1)your long-term romantic partner forming a deep emotional attachment to another person/ (2) your partner enjoying a passionate sexual intercourse with that other person • Men were significantly more likely to choose (1) as being more distressing/women were more likely to select (2) as being more distressing • If sexual jealousy is designed by NS to reduce a man’s risk of cuckoldry, then men should respond to cues of such risks in jealous ways – observed by Flinn (1988) – recorded at regular intervals the behaviour he came across in a Caribbean village – being mated to a fertile woman (reproductive age, not currently pregnant and could become pregnant) leads to more conflict within the relationship (especially if the relationship was not sexually exclusive) and with sexual rivals • This conflict over a man’s sexual exclusivity over his mate can escalate quite dangerously – can lead to domestic assault and homicide • Sexual jealousy is a common motive for domestic violence – far more commonly the cause of male-perpetrated violence than female-perpetrated violence • Historical laws in a variety of different places consider adultery (a violation of sexual exclusivity) a crime against the husband/male partner in the relationship but often do not accord women the same legal protection • Many legal systems once considered women to be the property of men – property of fathers before marriage and the property of their husband once married – women have demanded and achieved a legal status equivalent to that of men - men have been obliged to acknowledge women’s agency and right to autonomy Section 5: Kinship and Human Affairs Social Behaviour • Actions that affect the individual’s performing them and other individuals as well • Performing an action in self-interest in Darwinian terms: if an individual performs a behaviour that improves its own fitness, then the genes promoting it would be selected for and the behaviour will eventually become widespread • Ex. of helping behaviour: e
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