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Unit 3C:
Biological Bases of Behavior:
Genetics, Evolutionary
Psychology, and Behavior
Introduction
• Behavior genetics
–Heredity versus the environment
–Nature – genes
–Nurture – environment
Genes: Our Codes for Life
• Chromosome – DNA
structures that include
genes (46 total – 23
from each parent)
• DNA (deoxyribonucleic
acid)
• Genome- the
complete instructions
for making an
organism (human or
other)
Twin and Adoption Studies
Identical Versus Fraternal Twins
• Identical twins – same genes, but maybe not the same
# of copies or could have separate placentas
• Fraternal twins – separate altogether, but may carry
similar risks for disease- even divorce! (for all twins)
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Separated Twins
• U of MN studies on
identical twins separated
at birth – read book for
variety of stories!
• Despite criticisms, the striking
twin-study results helped shift
scientific thinking toward a
greater appreciation of genetic
influences.
Twin and Adoption Studies
Biological Versus Adoptive Relatives
• Who contributes more
genetic parents or
adoptive parents?
– People who grow up together
do not resemble one another
in personality
– Environment does not have as
much of an affect on children
Heritability
• Heritability
–the extent to which variation among
individuals can be attributed to their
differing genes
–“difference among people”
–We can never say what percentage of
an individual’s personality or intelligence
is inherited.
• genetic influence explains 50 percent of the observed
variation among people.
Heritability
Nature and Nurture
• Influence of adaptation- is our
enormous adaptive capacity
• Nature and nurture work together
–Our shared biology enables our
developed diversity
Gene-Environment Interaction
• Genes and experience interact
–Evocative interactions
– Environments trigger gene activity.
– Children experience different parents,
depending on their own qualities
– Our genes affect how people react to and
influence us.
– Biological appearances have social
consequences.
The New Frontier: Molecular Genetics
• Molecular genetics
–The goal of molecular behavior
genetics is to find some of the
many genes that influence
normal human traits, such as
body weight, sexual
orientation, and extraversion, and
also to explore the mechanisms
that control gene expression
Natural Selection and Adaptation
• Evolutionary psychology
– Natural selection
– among the range of inherited trait variations,
those contributing to reproduction and survival
will most likely be passed on to succeeding
generations.
• Organisms‘ varied offspring compete for survival.
• Certain biological and behavioral variations increase organisms‘
reproductive and survival chances in their particular environment.
• Offspring that survive are more likely to pass their genes to
ensuing generations.
• Thus, over time, population characteristics may change.
Evolutionary Success Helps Explain
Similarities
• Behaviors that contribute to
survival are found
throughout cultures
• Our adaptive flexibility in
responding to different
environments contributes to our
fitness—our ability to survive and
reproduce.
Evolutionary Success Helps Explain Similarities
Outdated Tendencies
• Genetic traits which helped our
ancestors survive may harm us
today
Evolutionary Success Helps Explain Similarities
Evolutionary Psychology Today
• Evolutionary psychologists have addressed questions such as
these:
– Why do infants start to fear strangers about the time they
become mobile?
– Why are biological fathers so much less likely than unrelated
boyfriends to abuse and murder the children with whom
they share a home?
– Why do so many more people have phobias about spiders,
snakes, and heights than about more dangerous threats,
such as guns and electricity?
– Why do humans share some universal moral ideas?
– How are men and women alike? How and why do men‘s and
women‘s sexuality differ?
An Evolutionary Explanation of Human Sexuality
Natural Selection and Mating Preferences
• Differing preferences in partners
–Male preferences
–Female preferences
Critiquing the Evolutionary
Perspective
• Backward theorizing
• Impact of social influence
The End
Definition
Slides
Behavior genetics
= the study of the relative power and limits of
genetic and environmental influences on
behavior.
Environment
= every non-genetic influence, from prenatal
nutrition to the people and things around
us.
Chromosomes
= threadlike structures made of DNA
molecules that contain the genes.
DNA (deoxyribonucleic acid)
= a complex molecule containing the genetic
information that makes up the
chromosomes.
Genes
= the biochemical units of heredity that make
up the chromosomes; segments of DNA
capable of synthesizing a protein.
Genome
= the complete instructions for making an
organism, consisting of all the genetic
material in that organism’s chromosomes.
Identical Twins
= twins who develop from a single fertilized
egg that splits in two, creating two
genetically identical organisms.
Fraternal Twins
= twins who develop from separate fertilized
eggs. They are genetically no closer than
brothers and sisters, but they share a fetal
environment.
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.
Interaction
= the interplay that occurs when the effect of
one factor (such as environment) depends
on another factor (such as heredity).
Molecular Genetics
= the subfield of biology that studies the
molecular structure and function of genes.
Evolutionary Psychology
= the study of the evolution of behavior and
the mind,using principles of natural
selection.
Natural Selection
= the principle that, among the range of
inherited trait variations, those that lead to
increased reproduction and survival will
most likely be passed on to succeeding
generations.
Mutation
= the random error in gene replication that
leads to a change.