Download 19. Nature vs Nurture PPT

CREATE A CHART: NATURE VS. NURTURE
The Nature-Nurture
Debate
Nature or Nurture?
Nature and Nurture?
NATURE
• The view of the
NATIVISTS
• “Nature” here refers
not simply to abilities
present at birth but to
any ability determined
by genes, including
those appearing through
maturation
NURTURE
• The view of EMPIRICISTS
• Everything is learned
through interactions
with the environment,
the physical and
social world, more
widely referred to as
‘experience’
Example:
The Entrepreneur
• Discuss - Is the person who starts up a business born with the
necessary independent drive, interpersonal skills and creativity
etc. “born to run a business”, or are these things mostly learned?
•
Researchers followed more than 5,500 students and graduates of five
universities:
• Initial results indicate that students who take entrepreneurial
courses are more likely to launch, run or be employed by a start-up
than others
• The more insightful finding is that students who took an
entrepreneurial course were more innovative than company
founders who didn't:
• Those students had far more patents or copyrights (75% vs. 19%),
new production processes (62% vs. 28%), and new services or
products (86% vs. 18%). So much for the "nature" philosophy.
Hypothetical Example:
Twins with the MAOA Gene
• The MAOA gene comes in multiple variants:
– those with the AH variant of the gene are optimistic and resilient
to bad treatment
– Those with the AL variant react strongly to maltreatment, and
often develop antisocial behaviour in response to it
• Imagine identical twins, both with the AL variant, are separated at
birth:
– one was adopted by a loving family
– the other was adopted by an abusive family
• Discuss:
Which child has the greater chance of becoming antisocial?
Clearly, the one raised in the abusive family would have a greater chance of
becoming antisocial
Just because the outcomes are different does not mean that the behaviour isn't
100% genetic. The environmental scenario detection is built into the design of
the genes (i.e. the brain circuitry designed by the genes)
How About You?
• Can you think of something about you that is clearly the result of
what you were born with?
– Please share with the class...
• Can you think of something about you that is the clear result of
how you have been raised, or of the experiences you have had?
– Please share...
NATURE
NURTURE
• Plato, the Greek
philosopher, believed
that a child began
life with knowledge
already present within
him.
• 17th century, the
French philosopher
René Descartes argued
similarly
• English 17th century
empirical philosopher
John Locke, said that
there were no innate
ideas
• He believed that the
mind at birth is like
‘white paper void of
all characters’, a
‘blank slate’
NATURE
NURTURE
Darwin’s theory suggested
• The behavioural
that traits were inherited,
theories championed by
which influenced early
Watson(1913) and
psychologists
Skinner(1938)
explained all
behaviour solely in
• James(1890) believed
terms of experience
that humans beings
had innate tendencies
which determined
natural selection
NATURE
• 1950s - Chomsky challenged the behaviourist
account of language acquisition: it happened
not just through experience but because human
children had an innate language module in the
brain
• Also in the 1950s, Burt was promoting the idea
that IQ is inherited
• The latest move away from ‘blank slatism’ is
evolutionary psychology, which explains
behaviour in terms of innate factors
NATURE
NURTURE
Evolutionary psychologists
assume that behaviour is a
product of natural
selection
Behaviourists assume
all behaviour can be
explained in terms of
experience alone
E.g. - Interpersonal
attraction can be
explained as a consequence
of sexual selection – men
and women select partners
who enhance their
reproductive success
E.g. Skinner(1957)
proposed that a child’s
acquisition of language
could be explained
entirely in terms of
rewards and shaping
NATURE
NURTURE
• Gibson(1979) argued that
perception is entirely
innate
• Gregory(1972) pointed to
the ambiguous and
fragmentary nature of
most sensory input
• The sensory array is
sufficiently rich in
information for
perception to take place
without any additional
cognitive input
• Perception must thus rely
on expectations (derived
from experience) to
complete the perceptual
process
Nature affects Nurture
Nurture affects Nature
Genes may affect behaviour
directly or may exert an
indirect effect in a number
of ways
Experience effects innate systems.
The brain has the ability, during
development and adulthood, to be
changed by experience.
E.g.
A new study suggests young
people are more likely to become
addicted to cigarettes if they carry
a specific form of a gene that helps
clear nicotine out of the liver.
E.g.
Pascual-Leone et al.(1995) found the
region of the brain that controls
finger movement increased in size in
participants who played a piano
finger exercise daily over only 5 days
NATURE
NURTURE
• Twin studies - .85 correlation in
IQ among identical twins vs. .60
correlation among non identical
twins
• Flynn Effect - Flynn showed that avge. IQ
scores over the world had risen over
generations, about 3 points per decade
• Authors of The Bell Curve Asian/Asian Americans have a
generally higher IQ than white
Americans who in turn have a
higher IQ than Black Americans
• Studies show IQ varies with:
• # siblings, malnutrition,
• # yrs in school,
• social group of the parent home
• parent professions & economic status
• parent ambitions,
• average book reading,
• emotional adaptation
NATURE
NURTURE
• Identical twins reared
apart show similar IQ
scores as those
reared together
• Schooling and intelligence influence
each other A 1997 study showed
that delays in schooling cause IQ to
drop 5 pts per year and a temporary
drop in IQ during school vacations
• This indicates that
intelligence is mostly
genetic
• Another study showed a 2.7 point
IQ advantage for each year of
schooling
Genetic and environmental contributions to cancers at 28
anatomical sites were studied in a sample of almost 45,000 pairs
of twins from the Swedish, Danish, and Finnish twin registries,
some cohorts going back to the 19th century
At least one cancer
occurred in ~11,000
persons among 9500
pairs of twins
Increased genetic risk
was shown for
stomach, colorectal,
lung, breast, prostate
cancers
Prostate cancer = 42% of risk explained by
heredity
Colorectal cancers = 35% due to heredity
Breast cancer = 27% due to heredity
The implication drawn is that more than half
the risk of cancer is due to the environment.
Virtually all is due to “unshared” environment
rather than common environments (e.g. family
diet, in home smoke exposure)
For cancer at the common sites in identical
twins, the rate of concordance is generally
less than 15 percent.
• The study has its limitations
• But is consistent with other results
• These results indicate a major
environmental role in carcinogenesis
• It’s not just the genes
It is said that a journalist once asked
psychologist Donald Hebb which
contributes more to personality,
nature or nurture?
In response, Hebb asked, “Which
contributes more to the area of a
rectangle, its length or its width?