Transcript PSY 226 Nature_Nurture_Mahoney_revised_9_9_2015

PSY 226: CHILD AND ADOLESCENT DEVELOPMENT
NATURE WITH NURTURE
Why are these kids…
…Depressed?
…Happy?
…Intelligent?
Learning Objectives
(1) Understand the following perspectives:
• Development is driven by nature.
• Development is driven by nurture.
• Development is part nature, part nurture.
(2) Be able to discuss how and why the
concept of heritability is flawed.
(3) Be able to discuss with examples the idea
that nature and nurture are parts of the
same whole and development is driven by
the process of epigenesis.
(4) Give examples of gene-environment
correlations (active, passive, evocative)
Genetic Myths
• Complex behavior(s) or
characteristic(s) such as
intelligence, aggression,
emotion, and obesity are
not caused by a single gene.
• There are no naked genes.
Genes are “wrapped” in
multiple contexts.
– Cell nucleus, cell, organ, organ system,
body and brain, multiple interacting
extra-organism contexts
Development is Driven by Nature
• Preformation – born to sin?
• Rousseau’s “innocent” babies
– Children are innocent at birth and
develop according to nature’s plan
• Genetic determinism and
eugenics (good genes)
– Individual cannot be changed by
nurture or education
– Advocate controlled breeding to
encourage childbearing among people
with “desirable” characteristics
Development is Driven by Nurture
• The Blank Slate
– Locke’s view of the mind “tabula rasa”
– Everything is the result of experience
• Watson’s Behaviorism
– Strict “fundamentalist” version of environmentalism
"Give me a dozen healthy infants, well-formed, and my own specified world
to bring them up in and I'll guarantee to take any one at random and train him
to become any type of specialist I might select--doctor, lawyer, artist,
merchant-chief, and, yes, even beggarman and thief, regardless of his talents,
penchants, tendencies, abilities, vocations, and race of his ancestors.
I am going beyond my facts and I admit it, but so have the advocates of the
contrary and they have been doing it for many thousands of years."
–John B. Watson, Behaviorism, 1930
Why are these extreme ideas
so popular?
VIDEO: Methods in Behavioral Genetics
http://study.com/academy/lesson/twin-and-adoption-studies-practices-findings.html
7:00
Fraternal and Identical Twins
Fraternal
“twins”
from
separate
eggs are
not any
more
geneticall
y alike
than
other
siblings.
To assess the
impact of nature
and nurture, how
do we examine
how genes make a
difference within
the same
environment?
Development is Part Nature, Part Nurture
• Heritability
– The extent to which a phenotypic trait* is due to genes
1. Twin studies
• H2 = 2 (rMZ – rDZ)
2. Adoption studies
3. Family relatedness studies
*A phenotype is an observable characteristic
resulting from ones genotype and environment
Heritability of Traits in Twins
Heritability Indices (Bouchard et al. 1990)
Height = .90
Intelligence (IQ) = .50
Personality (Big 5) = .50
Vocational/Recreational Interests = .50
Shared and Non-Shared
Environment
• Shared Environment – the environment that children
growing up in the same home have in common
– Parenting style, food choices, school system, neighborhood
characteristics
• Non-Shared Environment – the environment that
children growing up together do not share
– Sibling treatment, birth order effects, different peers,
classrooms, teachers
– Behavior geneticist argue that most of our home
environments are non-shared and that parents do not
matter very much anyway
Wait, What? Parents Don’t Matter?
Role Models
Albert Bandura’s social learning theory explains that
children learn by watching and imitating others (role
models). If so, then we should be able change behavior
by changing children’s experience of role models.
Imagine you’re a child development specialist. Using
Bandura’s social learning theory, what would you
advise the following parents to do?
Child Cases
1. Anura has a 2-year-old daughter and wants
her to love to read books.
2. Orpheus wants to encourage his 3-year-old
son to excel in art or music.
3. Sharna and Bronislaw are about to have a
child and want to him/her to be ecologically
responsible (recycle, use energy wisely, not
to be frivolous with money or waste food).
A 2014 Critique of Heritability
Behavioral Genetics Critique
I Hope My Partner
Read the Chapter
Think-Pair-Share
Identify 2 Criticisms of the
Concept of Heritability
Methodological Problems:
Twin Studies
• Equal Environment Assumption (EEA): The
environment of MZ co-twins is no more
similar than that of DZ co-twins.
• In what ways might this be wrong?
MZs are more likely than DZs:
•
•
•
•
to be treated more similarly by their parents
to brought up “as a unit”
to have the same friends
to be “inseparable” as children
– to spend time together
– to go out together
• to report greater closeness and mutual
influence
• to share bedrooms and clothes
• to share experiences like identity confusion
Ignoring this
inflates the
heritability
coefficient
Methodological Problems:
Twin Studies
• The Genderless Assumption (GE): It does not
matter if the DZ twins are same sex or
opposite sex.
• In what ways might this be wrong?
Kinship Studies:
Average Proportion of Genes Shared
Methodological Problems
• Believe it or not… the genderless and equal
environments assumption are usually followed
in kinship studies too (twins, siblings, cousins).
• Therefore, the environments of pairs of
opposite-sex cousins are deemed no less
similar than identical twins.
– Note: Cousins and siblings don’t share age either!
Methodological Problems:
Adoption Studies
• If we study siblings that have been adopted
apart, then that satisfies the equal
environment assumption.
• In what ways might this be wrong?
The Environments of Adoptees
are Selected (not random)
• Late separation
– Prenatal and early childhood influences can have
lasting effects
• Non-representative environments
– Seldom adopted to high risk settings
– Adopted parents are more affluent, educated, live in
better communities than the general population
•
Selective placements
–
–
–
–
They want to be parents
Parents are carefully screened
Parents want to participate in research
Least desirable kids and parents are matched
What if Environment
is Really Different?
What if the Twins’ Environment is
Really Different?
It is an impossibility…
“The only adoption study that would avoid such
[problems] would be one in which adoptees
were randomly assigned to parents, with both
groups blind to the treatment (i.e., not knowing
whether they were adopted or not) – all while
prenatal environment was held constant. In
other words, it is an impossibility to reliably
estimate genetic heritability using [the adoption
method]. (Conley, 2011; p. 597)
Conceptual Problems
• “Heritability studies rest on a model of
gene function that views genetic effects
as independent and separable from the
environmental context in which they
operate. Genes don’t work that way.
[They] are only one part of an
interactive, developmental
biopsychosocial system. …thus, it is
nonsensical to attempt to partition
genetic from environmental influences
on phenotypes.” (p. 225)
The Geno-Centric
Model of Behavior
Genes activate
themselves to code for
the production of protein
and build the person and
his/her personality.
Epigenetic Model
Epigenetic means “All around creation”
• DNA is not “self acting.” It is a catalyst and has
to be transcribed. It must first be activated.
• Whether genes stay dormant or turn on/off,
when and for how long, depends on the intracellular environment.
• The intra-cellular environment is affected by
the extra-cellular environment, and so on…
• The genome itself is dynamic and composed of
elements that undergo deletion, insertion, and
rearrangement.
Model of Behavioral Epigensis
• All levels of
organization interact
continuously over time.
• Genes effect and are
effected by this process
(co-effecting).
Conclusion
“Heritability studies do
not resolve the
outworn nature-versusnurture debate; they
promote it.”
“…we call for an end to
heritability studies…”
(p. 225)
Gene-Environment Correlations
• Active: The correlation between the child’s genetic
endowment and the choices the child makes about
which environments they will seek.
• Passive: The correlation between the genetic
endowment parents give their children and the
environments in which they place their children.
• Evocative: The correlation between the genetic
endowment of the child and responses the child
elicits from other people.
Capisce?
Gene-Environment Interactions
and Conception
Section A
Section B
The Remarkable Contributions
of Zing-Yang Kuo
Understanding Your Theoretical Potential
• The zygote (fertilized egg) starts to develop with an
extremely wide, but not unlimited, range of behavioral
potentials. Only a very small fraction can be realized.
• A more diverse the environment allows for more diversity in
behavior patterns.
• Usually the range of diversity in the environment is limited
so we see restricted range of behaviors. This can provide an
illusion of genetic determinism, particularly in early
development (e.g., instincts).
• BUT, if we manipulate the environment during development
we can create “behavioral neo-phenotypes” that are not
ordinarily observed.
Instincts and Experience
Even so-called “Instincts” such as a chicken pecking at
mealworms are malleable according to prenatal and
postnatal experience
a) Post-hatch pecking has developmental antecedents
prior to hatching (e.g., heart beat and head movements).
b) Post-hatch pecking has developmental antecedents in
early experience (e.g., visual, neuromuscular, balance).
“In other words, pecking is such a complex process of
prehatching and posthatching development, involving so
many morphological, physiological, and environmental
factors, that it would be quite naïve to argue whether it is
“innate” or “learned” or whether or not this behavior had
already been acquired in the shell.” Source: Kuo (1967; p. 109)
Instincts and Experiences
Kittens can be raised to be rat fearing, bird loving, to love some rats and kill
only shaved rats, or to kill mice while being friendly to white rats (pp. 6364).
Asian song thrushes (“predators”) can grow up to be eaters of small birds or
to be friendly and protective of them (p. 66).
Dogs – separated from their mother after birth – can be raised to prefer a diet
only consisting of soybeans, fruit and vegetables, or assorted foods even
when starving (p. 68).
“This can be accomplished without punishment or reward. Which is due to
nature and which is due to nurture?” (Kuo, 1967; p. 116)
“This means that it is impossible to pin down how much of trait is influenced
by genes. The heritability of a trait depends on the environment.”
(Steinberg et al., 2011; p. 58)
A Human Embryonic Stem Cell
“We are literally sitting on parts of body that might have been used for thinking!”
- Gilbert Gottlieb
Learning Objectives
(1) Understand the following perspectives:
• Development is driven by nature.
• Development is driven by nurture.
• Development is part nature, part nurture.
(2) Be able to discuss how and why the
concept of heritability is flawed.
(3) Be able to discuss with examples the idea
that nature and nurture are parts of the
same whole and development is driven by
the process of epigenesis.
(4) Give examples of gene-environment
correlations (active, passive, evocative)