Evolutionary Theory and Behavior Genetics

1. Evolutionary theory and species typical behavior

a) why individual differences?

(1) if something is important to survival, it should be selected for and there should not be within species variation
(2) balanced polymorphisms
- (a) the example of sickle cell
- (b) adaptive advantage of mid level of personality
  - i) approach traits
  - ii) avoidance traits

b) 5 types of competition

(1) between species
- (a) adaptation rates
- (b) sexual reproduction as a response to pathogens and parasites
(2) within species
- (a) intra-sexual competition for survival and reproduction
  - i) niche selection
  - ii) multiple strategies
- (b) inter-sexual competition for resources
  - i) maternity certainty and high investment
  - ii) paternity uncertainty and lower investment
- (c) parent-offspring competition
- (d) sibling competition
  - i) differential reproductive fitness as a function of birth order
  - ii) multiple strategies in response to birth order differences

2. Behavior genetics and the inheritance of individual differences

a) Behavior genetics: experiments of nature

(1) structural genes
(2) regulatory genes

b) The inheritance of cognitive and non cognitive aspects of personality

(1) experimental studies
- (a) rats and selective breeding
  - i) maze bright -- maze dull
  - ii) reactive, non reactive
- (b) dog breeding
(2) "simple" genetic models --Mendelian analysis
- (a) single gene models
  - i) multiple alleles
  - ii) additive genetic variation
  - iii) non-additive (dominant/recessive) variation
- (b) multiple gene models
(3) polygenic inheritance
- (a) simply the sum of separate genes
  - i) biometric analysis-- classic Mendelian analysis
  - ii) most likely for complex behavioral measures
- (b) analysis of genetic fragments
(4) the concept of heritability
- (a) Sources of variance
  - i) Vp = phenotypic variance in population
  - ii) Vg = additive genetic variance
  - iii) Vam = variance due to assortative mating
  - iv) Vd dominance deviation variance
  - v) Vi epistasis (interaction among genes)
  - vi) Ve environmental variation
    - (1) within family environmental effects
    - (2) between family environmental effects
  - vii) COVhe covariance of environment and genes
  - viii) Veg environment and genetic interaction
  - ix) Verror unreliability of measurement
- (b) Common misconceptions about heritability
  - i) heredity versus environment -- a meaningless question
    - (1) genes code proteins, not behavior
    - (2) genes act through the environment
  - ii) individual versus population
    - (1) variance estimates are population estimates, not for individual
    - (2) variations in environment affect estimates
  - iii) constancy
    - (1) heritability changes by changing any source of variance (h2=Vg/Vp)
    - (2) reducing environmental effects increases heritability
    - (3) heritability can increase with age
  - iv) measurement versus reality
  - v) Know all versus know nothing
  - vi) immutability
    - (1) within current environments
    - (2) by changing the environment
  - vii) genes act at birth
    - (1) some genes have late onset
- (c) empirical findings
  - i) consistency across studies and across nations
  - ii) for intelligence measures
    - (1) Rmza = .75
    - (2) Rmzt = .87
  - iii) for non-cognitive measures
    - (1) h2 ‰ .5±.2
    - (2) note that reliabilities are .7-.8

c) Designs

(1) Mono-zygotic twins reared apart
- (a) Shields' study
- (b) Bouchard/Minnesota Twin Study
- (c) Swedish Twin study
(2) MZ versus DZ twin designs
- (a) assumptions of equal environments
- (b) basic findings
  - i) cognitive measures
    - (1) intelligence
  - ii) non-cognitive
    - (1) extraversion
    - (2) neuroticism
  - iii) psychopathology
    - (1) schizophrenia
    - (2) depression
  - iv) attitudes
(3) adoption studies
- (a) the example of schizophrenia
- (b) decreasing similarity of adopteds reared together

d) Conclusions

(1) moderate additive genetic effect
(2) moderate environmental effect
- (a) but no between family environmental effect

e) implications

(1) for personality theory
(2) for clinical change
(3) for society