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The History of Behavior Genetics . How nature affects our genetics and how our genetics change how we perceive and deal with our environment. Leaving evolutionary and entering biological genetics…. Analogy: evolutionary psychologists : universal human tendencies

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the history of behavior genetics

The History of Behavior Genetics

How nature affects our genetics and how our genetics change how we perceive and deal with our environment.

leaving evolutionary and entering biological genetics
Leaving evolutionary and entering biological genetics…
  • Analogy:
  • evolutionary psychologists : universal human tendencies
  • behavior geneticists : differences in one another
  • What is the relationship?
sir francis galton
Sir Francis Galton
  • Sir Francis Galton, inspired by his cousin Darwin's Origin of Species (1859), pioneered the field of behavioral genetics.
  • Galton believed all human traits, including behavior, are solely determined by genes, without any contribution from the environment.
sir francis galton founder of eugenics
Sir Francis GaltonFounder of Eugenics
  • This idea became the basis for eugenics, a term Galton coined in 1883 to describe the use of genetics for social planning.
  • Galton, in other words, believed that selective "breeding" of the human species could guarantee that the "best" traits would remain in the human population while the "worst" traits could be eliminated.
sir francis galton founder of psychometrics
Sir Francis Galton Founder of Psychometrics
  • Psychometrics is the field of study (connected to psychology and statistics) concerned with the measurement of "psychological" aspects of a person such as knowledge, skills, abilities, or personality.
  • Critics, including "hard science" practitioners and social activists, have argued that such definition and quantification is impossibly difficult and that such measurements are very often misused.
this is what can happen when bad people hear good ideas
This is What can Happen When Bad People Hear Good Ideas
  • Based on Galton's ideas, the eugenics movement built momentum in the United States, where between 1905 and 1933, several states based laws and legal decisions on eugenics theory, and the federal government heavily restricted immigration from Eastern and Southern Europe.
  • The Immigration Restriction Act of 1924 limited total immigration to 165,000 — about 15-20% of peak years. More important, it restricted immigration from southern and eastern Europe countries to only 9% of the total. Northern and western European countries were allotted 86% of the quota, even though they made up the minority of immigrants in 1923. This change in the complexion of immigration was accomplished by a cunning use of statistics.
  • The Johnson Act limited immigrants from each country according to their proportion in the U.S. population in 1890 — a time prior to the major waves of southern and eastern European immigration when the U.S. was decidedly more Anglo-Nordic in composition.
this is what can happen when bad people hear good ideas1
This is What can Happen When Bad People Hear Good Ideas
  • The goal was the production of a genetically "pure" American population.
  • During this time in American history, criminals, people with low IQs and, in some cases, even women who had illegitimate children, were sterilized.
this is what can happen when bad people hear good ideas2
This is What can Happen When Bad People Hear Good Ideas
  • During its time in power, the government of Nazi Germany staunchly supported and enforced the principles of eugenics.
  • Eugenics-based legislation culminated in the "euthanasia" of the mentally retarded and the physically disabled, who, according to Nazi geneticists, would otherwise contaminate the German people with unfit genes.
this is what can happen when bad people hear good ideas3
This is What can Happen When Bad People Hear Good Ideas
  • The list of genetic undesirables ultimately grew to include Jews, Gypsies, Communists, Catholics, homosexuals, and political opponents of the government.
  • During the 1930s and 1940s, a large portion of the state's resources funded a system of death camps which, by the end of World War II, exterminated nearly twelve million people.
a swing back in the other direction
A Swing Back in the Other Direction
  • It was not until the 1980s that the scientific community began to pay serious attention to behavioral genetics as a science.
  • Using gene manipulation technologies which had been in the works since the late 1960s, geneticists could finally map the human genome itself.
a swing back in the other direction1
A Swing Back in the Other Direction
  • Since the early ’80s, geneticists have identified genes for cystic fibrosis, muscular dystrophy, and Huntington's disease.
  • The successes in identifying and mapping human disease genes have revitalized interest in identifying genetic factors underlying behavioral traits.
what behavior geneticists are studying
What Behavior-Geneticists are Studying…
  • Twin and family studies, genetic studies of animal behavior, biochemical investigations of mutations, and the development of new molecular approaches, have all added to the momentum of the modern search for genes influencing behavior.
the two main tools of a behavior geneticist
The Two Main Tools of a Behavior Geneticist:
  • The Goal: Behavior Geneticists must try to untangle the mystery between the influence of genetics (nature) and the environment (nurture).
  • The Tools:
    • Twin Studies
    • Adoption Studies
how many twins are out there
How Many Twins Are Out There
  • There are approximately 100 million twins worldwide.
  • The twin birth rate for fraternal twins varies slightly from country to country; identical twin birth rates are pretty much constant all over the world.
  • In Australia the twin birth rate is currently about 1 set of twins for every 80 births; there are a total of approx half a million twins in Australia.
types of twins






sex only

Same or

opposite sex

Types of Twins
  • (Identical Twins) Monozygotic twins develop when a single egg is fertilized by a single sperm and at some stage in the first two weeks the developing embryo splits in two, with the result that two, GENETICALLY IDENTICAL babies develop.
  • (Fraternal Twins) Dizygotic twins occur when two separate eggs are fertilized by two different sperm. These two fertilized eggs then develop independently. Dizygotic twins share the same type of genetic relationship as non-twin siblings, hence the term fraternal.
environmental influence
Environmental Influence
  • Two placental arrangements in identical twins
do twins run in the family
Do Twins Run In the Family?
  • A common question females ask is: "My mother (or sister, aunt or grandmother) had twins, what is the chance of me having twins too?" Fraternal (dizygotic) twins do tend to run in families. This is probably because there are genetic influences which make multiple ovulation more likely. There is no medical evidence of identical twins running in the family however there is some anecdotal evidence in support of it. Women who conceive when they are over 30 years of age also have an increased chance of having twins.
behavior genetics vocabulary
Behavior Genetics Vocabulary
  • Behavior Genetics
    • study of the power and limits of genetic and environmental influences on behavior
  • Environment
    • every nongenetic influence, from prenatal nutrition to the people and things around us
behavior genetics vocabulary1
Behavior Genetics Vocabulary
  • Temperament
    • a person’s characteristic emotional reactivity and intensity
  • Heritability
    • the proportion of variation among individuals that we can attribute to genes
    • may vary, depending on the range of populations and environments studied
behavior genetics vocabulary2
Behavior Genetics Vocabulary
  • Interaction
    • 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