Nature vs Nurture Flashcards
Phenotypic origins
individual differences, characteristics vary, quasi discrete, bi modal distributions
phenotypic trait
aspect of the organism can be mental or physical, myriad background factors and occasional events
Basic categories of explanation
nature = genetics, inborn biological blueprint
Nurture = environment, impinging external events
Neither = free will, uncaused rational volition
Triangle of destiny
three poles of possibility
1. Free will
2. Environment
3. Genes
Range from internal and innate
Genes - free will - environment
And causal determination and metaphysical freedom
Genes + environment - free will
free will
scientifically and philosophically problematic , perennially debated
Graham Young
example of idiographic triangle of destiny
Tea cup poisoner
Poisoned family members, one died
Convicted sent to prison
Released after 9 years as fully recovered
Proceeded to poison his of-workers, 2 died
Sent back to prison and he died
Why did he do it?
- genes - genetic makeup wrong?
- environment - upbringing wrong?
- free will - wrong choices?
Nature nurture debate
case extensively made on both sides, much accusation of bias by both sides
explanatory preferences partly reflect political vireos
right wing vs left wing
Accusation + constitutions vs conditions + extenuation
Genes
DNA - identical molecule inside every nucleus in the body, long strands of repeating nucleobases shaped like a double-helix, split into 23 chromosomes
Some gene code via RNA messenger for amino acids, building blocks of proteins = gene expression
Ultimately shapes features of the organism
Gene is a segment of DNA that may do some shaping
Mutations = mistakes in replication, source of biological variation
23 pairs of chromosomes, 23 from mum and 23 from dad, random which ones we inherit, inherit mutations too
Heredity vs inheritance
- heredity - passing on of phenotypic characteristics to offspring
- inheritance - the biological mechanism of heredity
- subtle distinction inborn effects can be due to genes, but not reflect heredity. All genes are inherited, but not all phenotypic characteristics are
Environment
more familiar and straightforward concepts (perhaps)
What surrounds the organism and often impinges on it
Note that the environment can be biological like genes
But is society biological
shared vs non-shared
Shared: those characteristics that are common to the environment of different people
Usually the overlapping family environment of kids, social status, parental income
Non-shared: those characteristics are unique to the environment of different people, usually the distinctive social environment of kids.
Heritability
genotype - yes, environment - yes
Phenotype - yes
Can you quantify variation?
Key formulae
VAR(Phenotype) = VAR(Genotype) + VAR(Enviornment)
Heritability = VAR(G) / VAR(G) + VAR(E)
Heritability = VAR(G) / VAR(P)
Heritability = H^2 (broad-sense) can be expressed as %
Heritability = VAR(G) contribution to VAR(P)
Non-heritability = VAR(E) / VAR(G) + VAR(E)
Non-heritability = VAR(E) / VAR(P)
Non-heritability = 100 - H^2
Non-heritability = VAR(E) contribution to VAR(P)
genes win
eye colour
- heritability approaches 100%
- Mendelian inheritance = a few genes responsible
- characteristics are strongly polygenic
environment wins
language and accent
- heritability is near 0%
- adopt language and accent of our community
Most other phenotypic traits
somewhere in between
- intelligence
- personality
- psychopathology
- height, weight, morbidity, mortality
- sex, gender, role orientation
genetic variance comes in three types
- Additive = VAR(GA)
- genes have independent effects on the phenotype - Dominant = VAR(GD)
- some genes tell others what to do, same locus - Epistatic = VAR(GE)
- some genes tell others what to do, different loci
All three add up into overall genetic variance
VAR(G) = VAR(GA) + VAR(GD) = VAR(GE)
Three types of combination
- Aggregation (G+E)
- effects of nature and nurture in inverse proportion - Interaction (G X E)
- effect of nature depends on nurture (or vice versa) - Influence (G<-> E)
- Effect of nature operate via nurture (or vice versa)
Aggregation
what we have discussed so far
There main types of combination
Quantify using behaviour genetic designs
interaction
some environmental factor operates only if or to the extent that some genetic factor is present
Some genetic factor operates only if or to the extent that some environmental factor is present
Diatheses-stress model - vulnerability to a potentially harmful factor - also a type of interaction
Epigentics phenomenon
- sometimes the environment can switch gene expression on or off
- one way this is done by adding or taking away chemicals - methylation / demethylation of DNA
- drugs and stress can act via this method
- biological/medical finding
- only speculative link to personality/ IQ so far
- genes make me smart to begin with - genetic effect on intelligence phenotype
influence
genes sometimes dispose people to choose environments which enable their expression
Virtuous circle (intelligence), or a vicious circle (aggression)
If nature facilitates nurture, which facilitates nature, can you separate logically in these cases?
Heritability is hard to intuitively determine
the cycle of violence
- abusive parents
- been abused so abuse own kids
- cycle continues short of an intervention
Separating environmental and genotypic variance
Var(G) ≈ 0; Var(E) ↔ Var(P)
Var(E) ≈ 0; Var(G) ↔ Var(P)
separating environmental and genotypic variance
- ethical and logical obstacles
- must capitalise on natural experiments, also compare to VAR(E) > 0 OR VAR(G) > 0
- assumptions not perfectly met, but may be adequate
