Nature, nurture or neither Flashcards
how can characteristics be displayed?
- Usually normally distributed (e.g. IQ, height, weight)
- Sometimes quasi-discrete and bimodal (e.g. sexual orientation, aesthetic preferences e.g. Marmite)
define phenotype
the sum of all of our traits or characteristics that we exhibit
what are the characteristics that make up our phenotype?
- mental characteristics (e.g. personality, intelligence, psychopathology)
- physical characteristics (e.g. health, illness, weight, height, sex, gender)
define phenotypic trait
any aspect of the organism - mental or physical
how can phenotypes and phenotypic traits be explained?
Myriad of background factors and occasional events that determine the phenotype or a phenotypic trait
Phenotypes and phenotypic traits can be explained using 3 categories:
nature, nurture or neither
explain ‘nature’ as an explanation for phenotypes
genes are caused - inborn biological blueprint - cannot be changed
explain ‘nurture’ as an explanation for phenotypes
environment is caused - impinging external events - can be changed/ targeted
explain ‘neither’ as an explanation for phenotypes
free will is a choice, caused by you - uncaused rational volition - many people do not belief in free will
what are the three poles of possibility in the ‘triangle of destiny’?
free will
genes
environment
which factors show causal determination?
Genes and environment are both deterministic as they cause the phenotype to be what it is
explain genes as a pole of possibility
genes are internal and innate
explain environment as a pole of possibility
environment in external and acquired
explain free will as a pole of possibility
free will is scientifically and philosophically problematic, difficult to explain, heavily debated but generally assumed to exist - metaphysical freedom
how does the triangle of destiny explain serial killers?
Genes - something wrong with their make-up?
Environment - something wrong with their upbringing?
Free will - something wrong with their choices?
how does the Big Five explain serial killers?
Serial killers tend to be:
○ Extraversion - low
○ Neuroticism - low
○ Conscientiousness - low
○ Openness - low
○ Agreeableness - low
○ Honesty-humility - low
how does the nature-nurture debate reflect political views?
Left wing people tend to focus more on external conditions that make people the way they are - fatalistic
Right wing people tend to focus more on personal responsibility and favour genes - free will and genes
what is DNA?
- Identical molecule inside every cell nucleus in the body
- Long strands of repeating nucleobases
- Shaped like a double-helix
- Split into 23 longer chromosomes
- Replicates reliably as new cells form
- Sometimes mutations are made
what are chromosomes?
- 23 chromosomes each from mother and father
- Random selection
what are genes?
- Code, via RNA messenger, for amino acids for gene expression
- Shapes features of the organism
- Segment of DNA that shapes how an organism develops
what are amino acids?
- The building blocks of proteins which produce physical expression
what are mutations?
- Causes biological variation between people
- Inherited from parents
- Some are good, most are bad
- Evolution produces variations
what is the theory of evolution?
- Random mutations of genes affecting behaviour
- Leads to organisms better or worse at surviving
- Organisms that are fittest to survive and reproduce pass on their successful genes to the next generation
what is a genome?
- Your complete DNA
what is the human genome?
- Average DNA for human beings
- Small variations in the human genome is what makes people different
what is a genotype?
- Aspects of DNA that make individuals unique
- Bearing on one or more particular characteristics
- Reflects alleles
what are alleles?
- Unique forms of your genes
- 1% difference between people produces individual differences
what does heredity mean?
- The observation that phenotypic characteristics of the parents are passed on to the offspring in subsequent generations
what does inheritance mean?
- The biological mechanism of heredity
what does heritability mean?
what is the difference between heredity and inheritance?
- Inborn effects can be due to genes but not reflect heredity. All genes are inherited, but not all phenotypic characteristics are
what is environment?
- What surrounds the organism and often impinges on it
- Can be biological e.g. the womb is the environment for a fetus, and nutrition is part of that environment - poses question: is society biological?
what is shared environment?
- Characteristics that are common to the environment of different people
- e.g. overlapping family environment of kids –> social status, parental income etc
- Freud said shared environment is very important
what is non-shared environment?
- Characteristics that are unique to the environment of different people
- e.g. distinctive social environment of kids –> special parental treatment, peer group etc
- e.g. random aspects of the environment –> noise around you
- For many characteristics, non-shared environment is more important
general calculation for phenotypes
Phenotype = genotype + free will + environment
Free will is not scientific so cannot be measured so…
Phenotype = genotype + environment
what happens when nature and nurture competes?
- Environment is more important than genes - variation in environment has a bigger effect on phenotypic variance than genes
- Genes are more important than environment - variation in genes has a bigger effect on phenotypic variance than environment
key formulae:
VAR(Phenotype) = VAR(Genotype) + VAR(Environment)
VAR(P) = VAR(G)+ VAR(E)
Plus 2 x COVAR(G, E) - can be ignored
Heritability = VAR(G) / VAR(G) + VAR(E)
Heritability = VAR(G) / VAR(P)
Heritability = H2 (Broad-sense): can express as %
Heritability = VAR(G) contribution to VAR(P)
additional formulae
Non-heritability = VAR(E) / VAR(G) + VAR€
Non-heritability = VAR(E) / VAR(P)
Non-heritability = 100 - H2
Non-heritability = VAR(E) contribution to VAR(P)
explain how eye colour works
- Heritability of eye colour is high (normally approaches 100%) - following simple Mendelian inheritance
- Only a few key genes are responsible for eye colour
- Most characteristics are strongly polygenic meaning lots of genes contribute to the expression - in these cases heritability is not approaching 100%
- Oodles of genes each contribute a tiny bit
explain how language and accent works
- Heritability of language and accent is low (normally near 0%)
- We adopt language and accent from our community
- Parents have less impact on the child’s accent
- Country itself has a bigger impact on influence of child’s accent
examples of traits that are genetically and environmentally explained
First law of behavioural genetics say that most traits are in-between
Intelligence, personality, psychopathology
Height, weight, morbidity, mortality
Sex, gender, role, orientation
Attitudes, belief in genes/ environment/ free will
what are the 3 types of genetic variance?
additive
dominant
epistatic
Adding up all three gives overall genetic variance: VAR(G) = VAR(GA) + VAR(GD) + VAR(GE)
VAR(GA) predominates so ignore VAR(GD) and VAR(GE)
what is additive genetic variance?
VAR(GA)
genes have independent effects on phenotype
what is dominant genetic variance?
VAR(GD)
some genes tell others what to do, at the same locus
what is epistatic genetic variance?
VAR(GE)
some genes tell others what to do, at different loci
what are the 3 different types of combination of genes and environment?
aggregation (G+E)
interaction (GxE)
influence (G<–>E)
what is aggregation?
○ Main type of combination
○ Effects of nature and nurture vary in inverse proportion e.g. more nature means less nurture and vice versa
○ Shows competition between genes and environment
○ Quantify using behaviour genetics design
○ Twin studies and adoption studies
what is interaction?
○ Effect of one depends on the other e.g. effect of genes depends on the environment and vice versa
○ 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
○ Diathesis-stress model is also a type of interaction
○ Aggressive illustration: does environmental abuse or bad genes (MAOA-L) increase aggression - how much does each depend on the other (interact)?
○ Epigenetics phenomenon: the environment can sometimes switch gene expression on or off e.g. drugs, stress
what is influence?
○ Effect of nature operates via nurture (or vice versa)
○ Genetic effect on intelligence phenotype –> genes affect environment choice –> environmental effect on intelligence phenotype
○ Genes sometimes dispose people to choose environments which further enable their expression - virtuous circle (intelligence) or vicious circle (aggression)
○ If nature facilitates nurture, which facilitates nature?
○ Example: cycle of violence
explain the cycle of violence
Abusive parents abuse their children –> children of abusive parents become abusive and go on to abuse their own children –> cycle continues
This says that environment is the explanation as you can observe the effects of parental abuse
However, parents are also passing on their potentially aggressive genes which cannot be observed
Situation is ambiguous but bias towards the visible
how can you separate environmental and genotypic variance using aggregate approach and competition approach?
separate out nature and nurture by: holding one constant (e.g. genotype) and varying the other (e.g. environment) then observing the variation in phenotype
what is the problem with separating environmental and genotypic variance?
○ Cannot conduct real experiments on humans as they are expensive and/or unethical
○ Must capitalise on natural experiments instead which is often criticised
○ Twin studies: MZ twins have same genes but can be reared together or apart which shows environmental effect - look at concordance rates for a characteristic and compare the difference between MZ and DZ twins
○ Adoption studies: adopted child has genes but not environment of biological parents and has environment but not genes of adoptive parents so if genes are more important, there will be a bigger concordance rate between biological family and child, whereas if environment is more important, there will be a bigger concordance rate between adoptive family and child
what does Falconer’s formula allow us to do?
Falconer’s formula allows you to compute the amount of heritability of a trait
- Shows that attitudes may be more genetic than environmental
- Shows that divorce may be genetic
- Shows that watching TV may be more genetic
what makes non-shared environment more important than shared?
- Common family environment that people grow up in doesn’t seem to impact how people turn out
- Behavioural genetic research suggests that many traits are due to the genes and/or non-shared environment rather than identifiable things like shared environment
e.g. weight may be more genetic than shared environmental
important things to note:
· Heritability cannot be computed for individuals as heritability is to do with variation across a group - there is no way to untangle the contributions of genotype and environment to the phenotype
· Heritability does not imply immutability as genes are hard to directly modify but their phenotypic result can be modified (e.g. hair can be dyed, PKU diet).
· Non-heritability does not imply mutability as some environments are difficult to change too
· Equalising the environment increases heritability as heritability depends on the ratio of genotypic variance to genotypic variance + environmental variance. If everyone is equal then environmental variance disappears, so only genotypic variance can account for phenotypic variance
