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Behavioral Genetics

Brian J. Piper, Ph.D.

Goals

• Genetics Primer

• Behavioral Genetics Methods– Selective Breeding– Pedigree Analysis– Twins (& Adopted Twins!)

• Evolutionary Psychology

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Gregor Mendel

• Austrian friar who studied pea plants (29K!)

• Dichotomous traits

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1822-1884

http://www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.php

Gregor Mendel

• Homozygote versus Heterozygote• Dominant versus Recessive

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1822-1884

http://www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.php

Examples of Mendelian Patterns

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S = spherical, s = wrinkled

Huntington’s Disease

• Neurodegenerative Disease– Loss of motor function

– dementia

H h

h Hh hh

h Hh hh

7http://en.wikipedia.org/wiki/Huntington%27s_Disease

1 min video: http://www.youtube.com/watch?v=JzAPh2v-SCQ

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Terminology

Chromosomes containing DNA (deoxyribonucleic acid) are situated in

the nucleus of a cell.

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Genes: Our Codes for Life

Segments within DNA consist of genes that make proteins to determine our

development.

Chromosome 4: Huntingtin gene;

Pedigree

Rife (1940) collected info from 2,200 college students and their parents

Parent ChildR X R = 7.6R x L or L x L = 21.6

Rife (1940) Genetics, 25, 178-186.

Aggression

• Brunner described an extended family in which 5 males had impulsive aggression including:

– Exhibitionism– Arson– Rape

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Limitations of Pedigree

• Paternity

• Best for Dichotomous Characteristics

• Families share environments too

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Selective Breeding

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• Simple procedure with extended history

• May involve controlling environment

• Has been completed for emotions and drug preference

• Limitations:– Generalizability– Ethics

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Twin Studies

Studying the effects of heredity and environment on two sets of twins,

identical and fraternal, has come in handy.

Logic

Relationship Genetic Relationship Predicted Similarity

Monozygotic Twins 100% High

Dizygotic Twins (same sex)

50% Moderate

Siblings 25% Lower

Unrelated Minimal Modest

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Logic

Relationship Genetic Relationship Predicted Similarity

Monozygotic Twins 100% High

Dizygotic Twins (same sex)

50% Moderate

Siblings 25% Lower

Unrelated Minimal Modest

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Temperament and Heredity

Temperament refers to a person’s stable emotional reactivity and intensity.

Identical twins express similar temperaments, suggesting heredity

predisposes temperament.

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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

Limitations of Twin Studies

• Is postnatal environment equivalent?– Non-randomness of adoptive families

• Is prenatal environment equivalent?– Solution: Assisted Reproductive

Technology

• Mechanism?

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Evolutionary Psychology: Understanding Human Nature

Evolutionary psychology studies why we as humans are alike. In particular, it studies the evolution of behavior and

mind using principles of natural selection.

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Topics of Evolutionary Psychology

A number of human traits have been identified as a result of pressures

afforded by natural selection.

Why do infants fear strangers when they become mobile?

Why do people fear spiders and snakes and not electricity and guns?

How are men and women alike? How and why do men’s and women’s sexuality differ?

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Natural Selection

Natural selection is an evolutionary process through which adaptive traits are

passed on to ongoing generations because these traits help animals survive

and reproduce.

Sex Differences in Cognitive Functions

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Yasen et al. (in review) Neuropsychobiology.

Sex Differences in Cognitive Functions

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Explanation: Males = Hunters Females = not

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Human Sexuality

Males and females, to a large extent, behave and think similarly. Differences in

sexes arise in regards to reproductive behaviors.

Gender Differences in Sexuality

Question (summarized) MaleFema

le

Casual sex 58% 34%

Sex for affection 25% 48%

Think about sex everyday 54% 19%

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Natural Selection & Mating Preferences

Natural selection has caused males to send their genes into the future by mating with multiple females since males have lower

costs involved.

However, females select one mature and caring male because of the higher costs involved with pregnancy and nursing.

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Mating Preferences

Males look for youthful appearing females in order to pass their genes into the future.

Females, on the other hand, look for maturity, dominance, affluence and

boldness in males.

Data based on 37 cultures.

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Critiquing the Evolutionary Perspective

Evolutionary psychologists take a behavior and work backward to explain it in terms of natural selection.

Evolutionary psychology proposes genetic determinism and undercuts morality in establishing society.

Summary

• Genetics Primer

• Behavioral Genetics Methods– Selective Breeding– Pedigree Analysis– Twins (& Adopted Twins!)

• Evolutionary Psychology

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Video: Genetics versus Environment in Dogs

• Behavioral Genetics: Dogs Decoded: Nova, 30:00 to 34:30

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