Download Genetics, evOlutionary psychology

Genes, twin studies, heritability,
Nature vs. Nurture
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Chromosomes: threadlike structures made of DNA
molecules that contain genes
Humans normally have 46 chromosomes, 23 from the
mother and 23 from the father.
Each chromosome is a coil of DNA (deoxyribonucleic
acid)
The DNA contain small segments called genes
Humans have approximately 30,000 genes
Genes can be active (expressed) or inactive
Genes can be turned on by environmental triggers,
which causes the gene to express
The genome contains all the genetic material in an
organisms chromosomes, in essence, the instructions
for making that organism
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To understand the influence of heredity and
environment, researchers would need to create
scenarios that either vary the environment but
not the heredity or vary the heredity but not
the environment.
It would be unethical to create these scenarios,
but nature has provided them.
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Identical twins
Formed from a
fertilized egg that
splits
monozygotic
Genetically identical
Also share same
prenatal
circumstances and
same cultural history
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Fraternal twins
develop from two
separate eggs
fertilized at the same
time
dizygotic
Share some prenatal
circumstances
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Identical twins have the
same genes but do not
always have the same
number of copies of
those genes (can explain
why one identical twin
is more likely to have a
disease)
Most share a placenta
but not all, could lead to
differences due to
prenatal nutrition
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Mirror twins: mirror
images of each other
example: one right
handed and the other
one left handed
May have different
personalities and
interests, show that
heritability of a trait
doesn’t mean it will
occur even in two
people who share the
same genes
There are and have been several twin studies
worldwide
Studies have shown that:
1)
Identical twins are more similar than fraternal
twins in both extraversion and neuroticism
2)
Disease risks are increased for identical twins
3)
Divorce risk (by examining rates) are about 50%
attributable to genetics
4)
Similar treatment does not predict psychological
behavior, in behavior genes matter
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Minnesota twin: Thomas Bouchard
Matt McGue and David Lykken (1992)
John Loehlin and Robert Nichols (1976)
Nancy Pederson(1988)
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Although, in studies by Pederson, identical
twins separated at birth had less identical
personalities than identical twins raised
together, they were more alike than fraternal
twins separated at birth.
Critics often point out that coincidences
happen and they we often share characteristics
with our age peers regardless of genetics
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Adoption creates two family groups: genetic
relatives and environmental relatives
One finding from studying adoptive families, is
that people who grow up together do not much
resemble each other in personality, regardless
of biology(McGue & Bouchard,1998)
In extraversion and agreeableness, adoptive
children resemble their biological parents more
than their adoptive parents
Environment seems to have no discernible
impact on personality development
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Why this is so and the impact of it fuels further
research into the topic
Adoptive environments do influence values,
attitudes, manners and faith/politics
So while genetics dominates personality
development, environment influences other
facets of the person
Adoptive families are often less likely to
experience child abuse , neglect and even
divorce
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In one study, (Bohman & Sigvardsson, 1990)
children who were adopted had fewer
problems than children who were registered
for adoption but the mother changed her mind
Even though at a greater risk for psychological
disorder, most adoptive children thrive
( Loehlin, 2007)
Many score higher on IQ tests than their
biological parents and have more stable lives
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Thinking about this information, the Pinker
TED talk and your own input/experience
Address the following quotes:
1) “We carry to our graves the essence of the
zygote that was first us.”
2) “The plural of anecdote is not data.”
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Heritability is the proportion of variation
among individuals that we can attribute to
genes.
Heritability may vary based on the range of
populations and environments studied
Adoption and twin studies have been used by
behavior geneticists to determine the
heritability of a trait—the extent to which
variation among individuals can be attributed
to their differing genes
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For example: if intelligence is determined to have
a 50% heritability, this does not mean that 50% of
your intelligence is genetic or inherited. It means
that genetic influence explains 50% of the variation
in people’s intelligence.
If environments were exactly the same, heritability
would rise; in situations where environments are
similar, heritability as a source becomes more
significant; if environments were less similar but
genetics were more similar, heritability would be
lower.
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Individual differences and group differences
cannot be explained in the same way.
For example: height and weight in individuals
are highly heritable ,but that will not explain
why we are taller and heavier today than our
ancestors. That is explained by
nutritional/environmental reasons not genetic
ones.
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Genes and environment work together. Genes code for
particular proteins but also respond to the
environment.
Genes are self-regulating and adaptive. For example; a
butterfly that is green in the summer turns brown in
the fall. The genes that produce the green coloring also
produce the brown coloring triggered by environment
and a temperature controlled genetic switch.
The genes react, instead of following a non-changing
blueprint.
This is why people with identical genes but differing
environment/experiences will often have similar but
not identical minds.
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Genes and environment are both important and
interact with each other.
Think more nature via nurture not nature vs. nurture
For example; 2 babies born, one with the predisposition
to be attractive, sociable and easygoing the other less
so. If the baby that is predisposed receives more
positive attention and stimulation it will grow into a
more outgoing and confident person. As a more
confident person, the child will seek activities that
further encourage social confidence.
The differences in the children’s personalities is caused
by the dance between genes and environment.
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A study of genes from the molecule up, to
determine which specific genes influence
behavior.
The goal is to identify some of the genes that
influence certain traits and to explore the
mechanisms that control gene expression.
Molecular geneticists are working on
pinpointing genes that can cause a wide array
of psychologically connected issues, such as:
alcoholism, bipolar disorder, depression, and
learning disorders.
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Evolutionary psychologists use Darwin’s principle
of natural selection to study the roots of human
behavior and mental processes.
1) Organisms’ varied offspring compete for
survival
2) Certain biological and behavioral variations
increase organisms’ reproductive and survival
chances in a particular environment
3) offspring that survive are more likely to pass
their genes to future generations
4) Thus, over time, population characteristics may
change
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Does natural selection explain human tendencies?
While nature has selected advantageous variations
from genetic mutations and from gene
combinations produced at conception, humans
genetic leash is looser than that of animals. Our
genes selected over years allow us to adapt to a
variety of environments and to learn. Genes and
experience together wire our brains. Our ability to
adapt and be flexible in responding to different
environments adds to our fitness—the ability to
survive and reproduce.
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Read page 104: Evolutionary success helps
explain similarities and paraphrase the main
concepts/ideas
Read page 107: Critiquing the evolutionary
perspective and paraphrase the main
concepts/ideas
Read pages 108-110: After reading “Reflections
on Nature and Nurture”, write about it. What
do you think? Did the passage trigger any
thoughts, feelings? If so, what are they?