Chapter 4 Nature, Nurture and Development
1. Heritability & Behavioral Genetics
2. Facultative Adaptation & Learning
- What are effects of genetic and environmental factors on behavior and
- Headlines like “67% of intelligence is due to genetics” are misleading. What does it
- Claim: All behavioural traits are heritable.
- e.g. TV watching - Does this mean there is a gene for TV watching? No!
- However, if you separate people into heavy internet use vs low internet use, there
might be some trait that is somehow linked with internet use.
- 2 Premises:
1) To extent that genetics is important:
genotypic similarity -> phenotypic similarity
“The more similar two people’s genes are, the more likely that they are similar
genotype: actual genes. phenotype: traits shown
2) To extent environment is important:
similar environment -> phenotypic similarity
Techniques used in genetic studies:
- Look at some traits (e.g. smart, sociable, aggression, psychotic, height)
- Family study:
- look at correlation between:
- individual and close relatives
- individual and more distant relatives
- Which correlations are higher?
- Problem: families may share or differ in environments.
- Look at correlations between:
- Adopted person & adopted family (e.g., parents, siblings)
- Adopted person & biological family (e.g., parents, siblings)
- Which correlations are higher?
- Look at correlations between
- Monozygotic twins (identical twins)
- Dizygotic twins
- If MZ twins show stronger correlation, implies importance of genetics.
Adoption twin study:
- Correlations between twins reared apart
- Correlations between twins reared together
Example: Correlation between IQ of:
MZ twins: 0.86
DZ twins: 0.60
Parent offspring: 0.42 Half-siblings: 0.35
Reared-apart biological relatives
MZ twins: 0.72
Reared together nonbiological relatives
Statistical estimate of proportion of variance on a given trait among individuals in a
given population that is attributable to genetic differences.
Example 1: There’s a insanely rich group of people. They all moved to an island and
raised their kids with the best of everything. Assume this provided the exact same
environment. Because the kids are different genetically, they will still have different
100m dash performance.
If they are in fact not at all related, and that the environment can be perfectly the
same for everyone, 100% of these variations in performance are genetic.
Example 2: 12 clones are sent off and raised in wildly different places since birth.
Then on their 18th birthday, they are brought together and their performance (dash
speed) is compared. In this case, none of the performance variation are attributable
1. Heritability score applies to particular group in particular environment at
e.g. height in rich countries vs country w/ disparity.
- So in the rich country, genetics might contribute more to height compared to
environment (which varies less in the country). -> higher heritability score
- And in the poor country, environment may contribute more. -> lower
- Take home message: heritability score is specific to a particular population.
2. Heritability does not inform about % contributions to individuals, just to
variance in group…
- i.e. you can’t say “80% of my intelligence is from genetics”
3. High heritability does not imply immutability:
- i.e. high heritability of a trait doesn’t mean the trait can’t be changed by
- e.g. everyone in a population is starving. Thus everyone is short due to
malnourishment. This means the heritability score will be very height. But this
doesn’t mean environmental factors have no impact.
4. Low heritability does not imply non-inherited.
- e.g. # of toes: there are almost no variation in # of toes due to genetic
variations, but how many toes you get is clearly inherited…
Amount of variation in a trait not attributable to inheritance.
Shared Environmental effects: (from sharing same family even if adopted)
e.g., SES, education level of parents, etc.
- Interesting fact: siblings are often alike than they think they are.
Non-shared Environmental effects:
Make family members different.
- Birth order.
- Events that happened before one sibling was born.
- Difference in education, peer groups…
- Gender differences
Dissimilarities in children of the same family:
.40 for cognitive abilities
.20 correlation for personality
.10 correlation for psychopathology (e.g., schizophrenia)
.05 correlations for personality
~0.0 for cognitive abilities by adolescence, and for psychopathology
What does this tell us?
- Maybe non-shared environmental effects matter more than shared environmental
- Maybe peer groups have more influence than your parents.
- For example, children who immigrated don’t have their family’s accent but the local
Adaptation that respond developmentally to specific environmental conditions/stimuli.
e.g., suntans, calluses.
As opposed to obligate adaptations these are adaptations selected by evolution such
as being able to see, sugar tasting sweet, which are developed regardless of the
environment we’re raised in.
But facultative adaptations like suntans will not develop if you stay inside all the time.
Many people think that some aspects of our psychology are a result of facultative
- For example, some people think that languages are facultative adaptations. We
only develop it when we are exposed to the language.
Two kinds of learning mechanisms
• Experience expectant
- Depend on stimuli/experiences reliably encountered in species-typical environment.
- Development of visual system and necessity of using eyes.
- People born with cataracts.
- When kids born with cataract get them treated and can see. Their visual
development are often handicapped, such as have trouble recognizing faces.
- Regions can take on other functions.
Critical (and sensitive) period - There’s a period of time when the brain is expecting a certain stimulation, such as
light entering the eyes that is essential to proper development.
- This might be similar to crowding. It’s possible that the parts of the brain that’s
supposed to be used to learn something was taken over by others.
- Depend on stimuli/experiences unique to individual
- not “timed” (i.e. no critical period)
- For example: no critical period for learning the Canadian national anthem.
- Learning the national anthem;
- Musician’s brain - there are differences in their brain related to playing instrument.
- Rat trained to bar press with one paw show differences in their brain.
The different kinds of learning debate.
- Skinner: learning happens by conditioning. Everything should be learned in the
- But we seem to be more prepared to learn certain things.
- Rhesus monkeys were raised in a lab (with no exposure to flowers or snakes)
- Initially they have no fear of snake or flowers. -> there is no innate fear of snakes.
- Some watched video of other monkey being scared of snake.
- The monkey was too scared to go past a toy snake to reach food. (Average time to
go past snake is higher).
- Others watched video of other monkey being scared of flowers.
- The monkey wasn’t scared to go past flowers to reach food.
(They also tried using crocodiles vs rabbits and got similar results)
Similar results in humans:
- Experiment show that kids (and adults) are quicker at identifying pictures of snakes
out of a group of pictures.
These are essentially facultative adaptations: monkeys only develop the adaptation
for fear of snakes if they are exposed to snakes.
- Two videos, one snake and one non-snake, are shown side by side on a projector.
The sound played is either a happy voice or scared voice.
- When the sacred voice is played, they watch the snake more.
- When the happy voice is played the other is watched more.
- This means if kids are given two emotions to match with snakes. They are
predisposed to associate fear with snakes.
These experiments may be proof for prepared learning - learning that is stronger
than would be expected by pure associations.
Chapter 5 Perceptual Development
Naive realism - Our senses give the world exactly the way it is.
Instinct Blindness - If a cognitive process is easy for us, we think it’s simple.
For example, identifying a man in a picture is easy for humans, so we think it’s
simple, but it’s in fact a complicated problem.
Taste & smell
At the end of pregnancy, the baby already has some sense of taste and smell.
Swallowing: Drinking and digestion of the amniotic fluid. Fetuses swallow amniotic
fluid. They injecte