Course: PSYC*1000 (DE)
Professor: Harvey Marmurek
Schedule: Summer, 2012
Textbook: Psychology – Tenth Edition in Modules authored by David G. Myers
Textbook ISBN: 9781464102615
Module 11: Behaviour Genetics and Evolutionary Psychology
What are our genes and how doe behaviour geneticists explain our individual differences?
• The plans for your own book of life run to 46 chapters – 23 donated by your mother’s egg and 23 by your
father’s sperm. Each of these 46 chapters, called a chromosome, is composed of a coiled chain of the
molecule DNA; genes are the small segments within that form the words of those chapters (20,000 to
o Genes can be active (expressed) or inactive
• Share 96% of our DNA sequence with chimpanzees
• Twin and Adoption Studies
o Identical Twins – monozygotic egg; genetically identical
Although identical twins have the same genes, they don’t always have the same number of
copies of those genes; explains why one may be more at risk of certain illness
Most share a placenta but 1 in 3 ha two separate placentas explaining some differences
o Fraternal Twins – dizygotic; womb mates
o Identical twin with Alzheimers may have 60% risk whereas fraternal’s risk is 30%
o Separated Twins – despite being separated for 38 years, virtually alike (Jim Lewis and Jim
99 identical and 200 fraternal twins separated – still, separated twins were more alike if
genetically identical than fraternal
Bouchard’s critics: “if any two strangers were to spend ours comparing their behaviours
and life histories, they would probably discover many coincidental similarities
• Biological Versus Adoptive Relatives
o Genetic relatives
o Environmental relatives
o Adoptees are more similar to their biological parents than to their caregiving adoptive parents
o The environment shared by a family’s children has virtually no discernible impact on their
o The genetic leash may limit the family environment’s influence on personality, but parents do
influence their children’s attitudes, values, manners, faith, and politics. A par of adopted children or
identical twins will, especially during adolescence, have more similar religious beliefs if reared
• Temperament and Heredity
o Heredity predisposes one quickly apparent aspec of personality – temperament, or emotional
Difficult, easy, and slow-to-warm-up
o The genetic effect appears in physiological differences
Anxious, inhibited infants have high and variable heart rates and a reactive nervous system
Put the following cell structures in order from smallest to largest: nucleus, gene, chromosome – gene, chromosome,
When the mother’s egg and the father’s sperm unite, each contributes 23 (chromosomes)
How do researchers use twin and adoption studies to learn about psychological principles?
Researchers compare the trait and behaviours of identical twins (same genes) and fraternal twins (sharing half their
genes – similar to any sibling). They also compare adopted children with their adoptive and biological parents.
Some studies compare twins raised together or separately. These studies help us determine how much variation
among individuals is due to genetic makeup and how much to environmental factors. What is the promise of molecular genetics research?
• Seeking to identify specific genes that influence behaviour
• Heredity influences body weight – but no single ‘obesity gene’
• A goal of molecular behaviour genetics is to find some of the many genes that together orchestrate traits
such as body weight, sexual orientation, and extraversion
• The most powerful potential for DNA is to predict risk so that steps can be taken to prevent problems before
• DNA scanning of fetus
o Ethical dilemmas – selective abortions
What is heritability, and how does it relate to individuals and groups?
• Using twin and adoption studies, behaviour geneticists can mathematically estimate the heritability of a trait
– the extent to which variation among individuals can be attributed to their differing genes.
• Genetic influence explains 50% of the observed variation among people
• Heritability refers to the extent to which differences among people are attributed to genes
• Individual differences in height and weight, for example, are highly heritable; yet nutritional rather than
genetic influences explain why,, as a group, today’s adults are taller and heavier than a century ago.
Those studying the heritability of a trait try to determine how much of our individual variation in that trait is due to our
How do heredity and environment work together?
• Among our similarities – our enormous adaptive capacity
o Walk around barefoot all summer, develop toughened, callused feet
o Genes and environment – nature and nurture – work together like two hands clapping
o Genes and experience are both different, but more precisely they interact
Environments trigger gene activity
Genetically influenced traits evoke significant responses in others
Epigenetics: study of environmental factors that affect how our genes are expressed
Molecular Genetics: study of the structure and function of specific genes
Behaviour Genetics: study of the relative effects of our genes and our environment on our behaviour.
How do evolutionary psychologists use natural se