1.1 - Interaction of Heredity & Environment

Psychology - the science of behavior & mental processes
○ Behavior = anything an organism does (any action we can observe & record)
○ Mental process = internal, subjective experiences (sensations, perceptions, dreams, thoughts, beliefs, &
feelings - cannot be observed)
● Central principle of psychology -
Everything psychological is also biological - every thought, mood, action, urge is
due to an internal biological event
The Nature-Nurture Issue
● Nature-nurture issue - biggest & most persistent issue in psychology; debate about the relative contributions that
genes (
nature) & experience (
nurture) make to the development of psychological traits & behaviors
○ Modern psychologists view traits & behaviors as an interaction between the two factors
● Natural selection - principle that inherited traits enabling an organism to survive & reproduce in a particular
environment will (in competition with other trait variations) most likely be passed on to succeeding generations
○ Proposed by Charles Darwin in his book
The Origin of Species (1859)
○ Theory was used in the 20th century to promote discriminatory or racist ideas with the idea of
eugenics,
or selectively breeding humans to promote certain characteristics
● Evolutionary psychology - study of the evolution of behavior & the mind, using principles of natural selection
○ Looks at how humans are
alike
● Behavior genetics - study of the relative power & limits of genetic & environmental influences on behavior
○ Looks at how humans
differ
●
Nurture works on what nature provides - our biology is the framework from which we start, & then our
environment shapes it
○ May be predisposed to depression (biological) & grow up in poverty (environment), thus increasing the
chances that you will suffer from depression
Evolutionary Psychology: Understanding Human Nature - How do evolutionary psychologists use natural
selection to explain behavior tendencies?
● Focus on what makes us
alike as humans using Darwin’s principle of
natural selection:
○ Organisms’ varied offspring compete for survival
○ Certain biological & behavioral variations increase organisms’ reproductive & survival chances in their
particular environment

Unit 1 - Biological Bases of Behavior
1. Module 1.1 - Interaction of Heredity & Environment
○ Offspring that survive are more likely to pass their genes to ensuing generations
○ In this way, over time, population characteristics may change
● Natural Selection & Adaptation:
○ Dmitry Belyaev mated 100 female foxes & 30 male foxes - from their offspring, he selected & mated the
tamest 20 percent (forced natural selection)
■ After 40 years of doing this, they created a new, tamer breed of foxes
○ Mutation - random error in gene replication that leads to a change
■ If the mutation has a positive effect, that will increase the likelihood that the mutated gene will be
passed on
○ Genes give us the capacity to
adapt to new environments, & experiences combined with genes increases
our
fitness - ability to survive & reproduce
● Evolutionary Success Helps Explain Similarities:
○ Only 5% of genetic differences among humans come from population differences; 95% of genetic
variation exists
within populations
■ Difference between two South Africans & two Singaporeans larger than the
average difference
between the groups
Behavior Genetics: Predicting Individual Differences - How do behavior geneticists explain our individual
differences?
● Behavior geneticists study the genetic & environmental roots of human differences
○ Look at interaction between:
■ Environment - every nongenetic influence, from prenatal nutrition to our experiences of the
people & things around us
■ Heredity - genetic transfer of characteristics from parents to offspring
● Biochemical units of heredity are known as
genes
○ Genome - complete instructions for making an organism
■ Common sequence within human DNA is what makes us human - but we are 96% percent
genetically identical to chimpanzees
●
Point to Remember: Our differing traits influenced by many genes of small effect

Unit 1 - Biological Bases of Behavior
1. Module 1.1 - Interaction of Heredity & Environment
Twin & Adoption Studies - How do twin & adoption studies help us understand the effects & interactions of
nature & nurture?
● To understand relative impact of nature & nurture, scientists would like to be able to control heredity while varying
the home environment, & control the home environment while varying heredity
● Identical (monozygotic) twins - individuals that develop from a single fertilized egg that splits in two, creating
two genetically identical individuals
○ Have same genes, but don’t always have the
same number of copies of those genes
○ One in three identical twins have different placentas (prenatal environment)
● Fraternal (dizygotic) twins - individuals who develop from separate fertilized eggs; genetically no closer than
ordinary siblings, but share a prenatal environment
● Behaviorally & physically, identical twins are more similar than fraternal twins
○ Use identical twins that have been separated at birth to study relative impact of environment
Point to Remember: Shared family environments have little impact on personality, but parenting does influence
other factors
Gene-Environment Interaction - How do heredity and environment work together?
● Interaction - interplay that occurs when the effect of one factor (such as environment) depends on another factor
(such as heredity)
● Epigenetics - study of the molecular mechanisms by which environments can influence genetic expression
(without DNA change)
○ Diet, drugs, stress, etc. - alterations can be passed down through generations (Holocaust survivors)