Transcript Memory

Behavior Genetics
Chapter 4, Lecture 1
“Genes and environment – nature and nurture –
work together like two hands clapping.”
- David Myers
Behavior Genetics: Predicting
Individual Differences
Behavior Geneticists study our
differences and weigh the relative
effects of heredity and environment.
Genes: Our Codes for Life
Chromosomes containing DNA (deoxyribonucleic acid)
are situated in the nucleus of a cell.
Genes: Our Codes for Life
Segments within DNA consist of genes that
make proteins to determine our development.
Genome
Genome is the set of complete
instructions for making an organism,
containing all the genes in that organism.
Thus, the human genome makes us
human, and the genome for drosophila
makes it a common house fly.
Now pair up with someone you don’t
know well and take a look at handout 4-2
Twin and Adoption Studies
Studying the effects of heredity and
environment on two sets of twins, identical and
fraternal, has come in handy.
Separated Twins
A number of studies compared identical twins
reared separately from birth, or close thereafter,
and found numerous similarities.
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate
Separated Twins
Critics of separated twin studies note that such
similarities can be found between strangers.
Researchers point out that differences between
fraternal twins are greater than identical twins.
Bob Sacha
Biological Versus
Adoptive Relatives
Adoption studies, as opposed to twin studies,
suggest that adoptees (who may be biologically
unrelated) tend to be different from their
adoptive parents and siblings.
Adoptive Studies
Adoptive studies strongly point to the simple
fact that biologically related children turn out to
be different in a family. So investigators ask:
Do siblings have differing experiences?
Do siblings, despite sharing half of their genes, have
different combinations of the other half of their genes?
Ultimate question: Does parenting have an effect?
Parenting
Parenting does have an effect on biologically
related and unrelated children.
Parenting Influences
Children’s
Attitudes, Values
Manners, Beliefs
Faith, Politics
Temperament and Heredity
Temperament refers to a person’s stable
emotional reactivity and intensity.
Identical twins express similar
temperaments, suggesting heredity
predisposes temperament.
Nature and Nurture
Some human traits are fixed, such as
having two eyes. However, most
psychological traits are liable to change
with environmental experience.
Genes provide choices for the organism to
change its form or traits when
environmental variables change. Therefore,
genes are pliable or self-regulating.
Gene-Environment Interaction
Genes can influence traits which affect
responses, and environment can affect
gene activity.
A genetic predisposition that makes a child
restless and hyperactive evokes an angry
response from his parents. A stressful
environment can trigger genes to manufacture
neurotransmitters leading to depression.
Heritability: the proportion of variation
among individuals that we can attribute
to genes. The heritability of a trait may
vary, depending on the range of
populations and environments studied.
Gene-Environment Interaction
Genes and environment affect our traits
individually, but more important are their
interactive effects.
Alessia Pierdomenico
/Reuters/Corbis
Rex Features
People respond differently to
Rowan Atkinson (Mr. Bean) than Orlando bloom.
Other interesting examples of geneenvironment interaction:
Girls raised in fatherless households experience puberty earlier.
“Apparently the change in timing,” writes Matt Ridley, “is the
reaction of a still mysterious set of genes to their environment.
Scientists don’t know how many sets of genes act in this way.”
Fear of snakes, the most common human phobia, seems
instinctive. Still, studies with monkeys indicate that their fear
of snakes (and most likely ours) must be acquired by watching
another individual react with fear to snakes. We inherit not a
fear of snakes but a genetic predisposition to learn a fear of
snakes.
Other interesting examples of geneenvironment interaction:
In contrast to chimpanzees, people have the capacity for complex,
grammatical language. However, language must be learned
from other language-speaking human beings. The capacity to
learn is shaped by genes that open and close a critical window
when learning can take place. If children are not exposed to
spoken language during this critical period, they will always
struggle with speech.
Other interesting examples of geneenvironment interaction:
Ray Blanchard’s research at the University of Toronto indicates
that gay men are more likely than either lesbians or heterosexual
men to have older brothers (but not older sisters). Apparently,
something about occupying the womb that has held other boys
occasionally leads to reduced birth weight, a larger placenta, and
increased likelihood of homosexuality. Blanchard suspects that
an immune reaction in the mother grows stronger with each
male pregnancy. This immune response may affect the expression
of key genes during brain development that increases a boy’s
attraction to his own sex. The explanation obviously does not
hold true for all cases of homosexuality, but it may provide
important clues into the origin of heterosexual as well as
homosexual orientation for some people.
Other interesting examples of geneenvironment interaction:
Evidence suggests that childhood maltreatment may produce an
antisocial adult. However, Terrie Moffitt, in New Zealand
studies, finds that this may be true for only a genetic minority. In
fact, those with high-active monoamine oxidase A (MOA) genes
are virtually immune to the effects of maltreatment; that is, they
do not become more antisocial. Those with low-active genes are
much more antisocial if maltreated, yet slightly less antisocial if
not maltreated. In short, maltreatment along does not produce
antisocial behavior; the low-active gene must also be present.
Similarly, the low-active gene alone does not produce antisocial
behavior; maltreatment must also occur.
Homework
Read p.143-149
“A visitor from outer space could drop in
anywhere and find humans dancing and feasting,
singing and worshiping, playing sports and
games, laughing and crying, living in families
and forming groups.”
- David Myers