biological theories

• What are the basic principles of evolutionary theory? 

• Darwin proposed 2 processes of evolution:

  • Natural selection 

    • Organisms who possess characteristics that enhance their ability to survive are more likely to live to reproductive age and pass these characteristics on to the next generation 

    • E.g: preference for sweet, fatty, and salty foods among humans 

  • Sexual selection 

    •  process where organisms develop characteristics that enhance their ability to reproduce 

      • ^ happens through 2 mechanisms:

        • intrasexual selection

        • intersexual selection

• Intrasexual selection (i.e. same-sex competition) vs intersexual selection  (i.e., female/male choice)

• Occurs when same sex organisms compete for the sexual interest of the opposite sex 

• Organisms who possess characteristics that enable them to ‘win’ the sexual interest of the opposite sex are more likely to mate and pass these characteristics on to the next generation 

  • E.g. aerial hover display of the make bronzed cowbird

• Occurs when organisms of one sex prefer to mate with organisms of the opposite sex who possess specific, desirable characteristics

• Organisms who possess characteristics that are desirable to the opposite sex are more likely to mate and pass these characteristics on to the next generation

  • E.g. the plumage of the male peacock

How have the basic principles of evolutionary theory been adapted to the study of personality?

• Evolutionary research on sex differences in personality is premised on sex differences in productive capacity and minimal parental investment 

  • Men have more reproductive capacity than females 

    • Females: 8 - 12 offspring across the lifespan 

    • Males: an almost unlimited number of offspring across the lifespan (maximum recorded to date: 900)

  • Men can have minimal parental investment 

    • Females: carry + nourish fetus for 9 months; nurse child after birth; during lactation, ovulation is suppressed 

    • Males: engage in copulation 

2 hypotheses of sex differences and their influence on mate preferences and sociosexuality

• Hypothesis A: sex differences have evolved in mate preferences: 

  • Males value appearance in a mate more than females

  • Females value resource potential in a mate more than males

    • Evidence: Buss + angleitner paper where participants rated characteristics for their desirability in a potential mate

• Hypothesis B: sex differences have evolved in sociosexuality

  • Sociosexuality (i.e. willingness to engage in uncommitted sexual contact) 

  • Males are higher in sociosexuality (e.g., seek more sexual partners, are less discriminating in choice of sexual partners) than females

    • Clark and Hatfield study where confederates approached students of the opposite sex on campus and females were more selective while men were not lol 

• Common criticisms of evolutionary psychology:

Theorists critique it as: unfalsifiable, controversial (heteronormative, heterosexist, etc), there are also alternative explanations

What are the goals of behavioral genetics? (3 goals)

• Goal 1: Determine the degree to which individual differences in personality within a population are caused by genetic factors vs. environmental factors

• Goal 2: identify genetic factors that contribute to individual differences in personality characteristics 

  • E.g. gene D4DR on chromosome 11 contributes to individual differences in ‘sensation seeking’ (i.e. novelty seeking)

• Goal 3: identify environmental factors that contribute to individual differences in personality characteristics 

  • E.g. non-shared environmental factors have greater influence than shared environmental factors on the personalities of siblings 

• Vp = Vg + Ve 

• • Vp → variation in an observable personality characteristic within a population 

  • Vg → Variation in the genetic factors that contribute to that characteristic

  • Ve → Variation in the environmental factors that contribute to that characteristic

• What are heritability and environmentalism and how are they assessed? 

• Heritability: proportion of phenotypic variance that is attributable to genotypic variance

  • E.g. heritability of aggression = .67 

    • Means 67% of observed variance in aggression within a population is due to individual differences in genetic makeup 

• Environmentality: proportion of phenotypic variance that is attributable to variance in environmental factors 

  • E.g. environmentality of ambition = .62

    • 62% of observed variance in ambition within a population is due to individual differences in environmental factors 

• Assesed through: 

  • Adoption studies 

  • Twin studies 

• What personality characteristics are heritable? 

• All personality characteristics studied to date show some degree of heritability; most personality characteristics have a heritability between .40 and .60

• Heritability of temperaments 

• Temperaments appear during the 1st year of life, persist across the lifespan, have a pervasive influence on behaviour, and are highly heritable 

  • E.g. activity level, emotionality (Degree to which an individual becomes physiologically aroused (anger, distress, fear) in upsetting situations)

• Heritability of dimensions of the five-factor taxonomy 

• • Agreeableness = .42 

  • Conscientiousness = .49 

  • Extraversion = .54

  • Neuroticism = .48 

  • Openness to experience = .57

• Heritability of personality disorders 

• Antisocial = .69 

• Avoidant = .67 

• Borderline = .67 

• Narcissistic = .71 

• Obsessive-compulsive = .53 

• Schizotypal = .72 

• High degree of heritability of characteristics associated with psychopathy 

• compute heritability and environmentality from the findings of twin studies

• Heritability = 2(r1-r2) 

• Environmentality = 1.00 - heritability 

discuss genotype-environment correlations (3)

• Passive genotype-environment correlation

  • occurs when parents passively provide a gene-conductive environment for their children, encouraging the expression of their children’s genetic predispositions 

• Reactive genotype-environment correlation:

  • Occurs when parents actively provide a gene- conductive environment for their children, encouraging the expression of their children’s genetic predispositions 

• Active genotype- environment correlation (‘niche picking’) 

  • Occurs when individuals with a genotype create or seek out gene-conductive environments, encouraging the expression of their own genetic predispositions 

• Behavioral genetics cannot be applied to individuals due to these ^^^

• Phenotypic and genotypic variance (in relation to heritability) 

• Phenotypic variance 

  • Individual differences in an observable characteristics (e.g., height, aggression, extraversion) 

• Genotypic variance 

  • Individual differences in genetic makeup 

adoption studies vs twin studies

adoption:

• Contrast adopted children to their biological parents and adoptive parents on a characteristic of interest

  • Assess 2 correlations: 

    • r1 : correlation between adopted children’s scores and the scores of their biological parents on the characteristic (influence of shared genes) 

    • r2: same as r1 but influence of shared environment

    • If r1>r2, indicates that the personality characteristic is heritable 

• Criticism: adoption studies do not correct for ‘selective placement’ (i.e. the possibility that adopted children are placed with adoptive parents who are genetically similar to their biological parents ) 

twin:

• More powerful than adoption studies 

• Contrasts monozygotic (100% of genes shared) twins to dizygotic (50% of genes shared) twins on a characteristic of interest 

• Assesses two correlations: 

  • r 1 : Correlation between MZ twins on the characteristic (large degree of genetic overlap) 

  • r 2 : Correlation between DZ twins on the characteristic (small degree of genetic overlap)

  • If r1>r2, indicates that the personality characteristic is heritable

• Criticism: 

  • Twin studies do not correct for the “equal environments assumption” (i.e., they assume that MZ twins are not treated more similarly than DZ twins)

What does contemporary research suggest about the physiological basis of (a) extraversion

• a.) eysenck’s theory: extraversion is linked to the ascending reticular activation system (ARAS) in the brainstem, which regulates cortical arousal 

  • Introverts: have high ARAS activity, leading to high baseline cortical arousal. They seek low stimulation environments to avoid over-arousal  

  • Extraverts: have low ARAS activity, leading to low baseline cortical arousal. They seek high- stimulation environments to increase arousal 

  • fMRI evidence: extraverts and introverts differ in arousability (responsiveness to stimuli) rather than baseline arousal, partially contradicting eysenck’s original theory 

What does contemporary research suggest about the physiological basis of sensitivity to reward and punishment

• sensitivity to reward and punishment 

  • Grays theory: two systems regulate sensitivity to reward and punishment 

    • Behavioral Activation System (BAS): Located in the left prefrontal cortex, linked to dopamine. It responds to rewards, generates positive emotions (e.g., excitement), and regulates approach behavior. Associated with differences in extraversion.

    • Behavioral Inhibition System (BIS): Located in the right prefrontal cortex, linked to serotonin, GABA, and norepinephrine. It responds to punishment, generates negative emotions (e.g., anxiety), and regulates avoidance behavior. Associated with differences in neuroticism.

What does contemporary research suggest about the physiological basis of sensation seeking?

• Zuckerman’s Theory: Sensation seeking is linked to low levels of monoamine oxidase (MAO), an enzyme that breaks down neurotransmitters like dopamine.

  • MAO act as a “brake,” inhibiting neurotransmission + SSeekers have relatively low MAO, resulting in relatively high neurotransmission of dopamine 

  • Low MAO leads to high dopamine levels which causes disinhibition (reduced control over behavior, thoughts, and feelings).

  • Sensation seekers are drawn to novel, exciting, and risky experiences due to high dopamine levels 

• discuss the influences of the BAS and BIS on learning and psychopathology

• Learning:

  • BAS: Promotes learning through reward-seeking behavior (e.g., positive reinforcement).

  • BIS: Promotes learning through punishment avoidance (e.g., negative reinforcement).

• Psychopathology:

  • BAS Dysregulation: Overactive BAS may lead to impulsivity, risk-taking, and disorders like mania.

  • BIS Dysregulation: Overactive BIS may lead to anxiety, fear, and disorders like generalized anxiety disorder.

• define sensation seeking (SS)

• The tendency to seek novel, exciting, and risky experiences. It includes traits like thrill-seeking, disinhibition, and boredom susceptibility.