Gonna look at biological influences on personality,
Start by differentiating between traits and types,
Types refer to discontinuous categories, these are discrete categories, and everyone
fits into one.
Traits are more like measuring sticks; align ppl along a continuum/ metric
William Sheldon’s theory of somatotypes
Psychological characteristics go along with each of these physical types.
Ectomorph tends to be taller skinnier, tends to have less muscle effort put towards
Endomorphs more sociable, take pleasure from bodily sources, eating/sex etc,
characterized by inertia and sluggishness,
Mesomorph had muscle, were less intellectual.
Consider a problem: some of you may say: if someone doesn’t have muscle they would
pursue intellectual tasks, and if ppl are athletic they play sports. But it may just be
Sheldon may be right, but for dif reasons. Maybe their parents told them to go into certain
things. So skinny kids parents say “go to intellectual things”
An approach to (not a subdiscipline of) psychology that considers species-wide
universals through the lens of adaptive problems faced by ancestors
Looks for universals in humans, and considers current behaviors through the lens of
”human ancestors” that were in some environment in the past
Key assumptions they make: 1. The brain is a physical system, with neural ‘circuits’
(hunk of meat in the body) (brain is like a circuit board with a bunch of circuits)
2. These ‘circuits’ were shaped by selective pressures to solve problems that
influenced reproductive success
3. Functional specialization domain-specific circuits as opposed to broad neural
plasticity (‘Swiss Army Knife’ each tool is specialized for a certain task)
( there is modularity, idea of modules) (specific areas of the brain that have developed to
solve specific problems, as opposed to the view of the brain being broadly plastic
where one part of the brain can take over for another part of the brain etc.) [there is a lot
of evidence for neural plasticity]
Evolution doesn’t have a goal, animals don’t sit around and go “so there’s fruit and we
can’t eat it, so let’s make babies that eventually get a mutation that can eat it”
4. “Stone age brains in space age skulls”
Humans evolve very slowly, (at very least we need 12/13 yr old cuz that’s when they can
culture evolution will always out-pace biological evolution in humans.
You have to be sceptical environment we have now is very different culturally compared
to our ancestors.
Cultural changes occur faster than biological changes.
Not looking to explain universals among people. Rather, they are trying to look for
genetic explanations for within species or population variability.
(so evolutionary psychologist look for universals to help explain, “why all people or
most people do X”) Wheras behaviour geneticists are concerned with “why is it that
some people do X and some people do Y? and is there a genetic underpinning for this
They also consider environmental factors, not just genetic factors.
Considers hereditary and environmental factors as a source of within-species behavioural
variability Key methods used:
1. Family studies
Idea is : if a behavior is heritable, we should see some transmission between
parent and child. So if we study the parent and then study children based on
personality metric for a trait, we should be able to see some transmission from
parent to child.
Problem: It could be due to socialization factors that kid has bad manners, so is
the misbehavior due to some biological temperament they have or is it something
that has been taught by the parents (child modeling the parent)
So family studies don’t prove that there is a genetic basis, but it provides us evidence that
is compatible or incompatible with the theory of genetic basis. Correlation between
parent and child is a necessary factor to prove genetic basis, but it’s not a sufficient factor
there could be other explanations for this.
Schizophrenia General public 1%
Parents of schizophrenics 5.6 %
Siblings of schizophrenics 10.1 %
As a general rule, as we get less related there is less overlap in terms of schizophrenia
Suggests genetic component is at work, but it doesn’t tell us how strong it is relative to
2. Adoption studies
Look t correlation between children that have been adopted and their birth parents. So
earlier the kid is taken away from biological parent, the less the environment can be a
Adoption is not completely random, there is a selection / matching process
So kid raised til age 5, and then parents die, so they try and get the id adoption parents
that were like their original parents, and the problem this creates is that “we think we
have taken the shared environment out of the equation but we haven’t” cuz the adoptive
rents are acting just like their birth parents would have. So then some of these adoptive
studies begin to look like family studies again.
May have non-representative sample ppl that put kids up for adoption, or ppl that
adopt kids may or may not differ in some significant ways from people that don’t gve up
their kids for adoption (wealth/health related factors)
3. Twin studies
See if environmental fcators can make twins that were initally similar, different