PART 1: BACKGROUND

• Socrates cited the example of a man with no previous training in geometry solving difficult proofs (think Good Will Hunting).
• Socrates claimed that the man was born with the knowledge and had only now discovered that he had it.

• Locke claimed that each child was born with a blank slate as a mind (tabula rosa), and that this mind could then be molded into anything.
• Locke claimed that it was the duty of parents and society to build this child into anything the deemed fit.
• This is similar to Rousseau’s happy savage idea.

• Mendel discovered the idea of heritability of traits in plant life (think eye color, or body mass).
• Darwin’s study of natural selection indicated that certain genetic mutations proved to be adaptive, and these mutations were then passed down to the survivors off spring.
• Galton (1822-1911) was interested in individual differences.
• Galton wrote "Hereditary Genius" in 1869, which was a study of eminence.
• Galton created the correlation coefficient, which was perfected by his student Pearson.
• Galton is not mentioned often do to his advocacy of the science of eugenics, that is, improving the human race through genetics.
• Eugenics was popular with scientists in the 1920’s, and not just the Nazi’s.
• By 1927 the U.S. had made eugenics policy, and were sterilizing people deemed as incompetent or inferior. Further, the immigration of peoples from southern Europe was restricted. (Slave owners also used Eugenics, but they called it breeding).

• Watson believed that anything could be taught anything. And was once heard to say that if given enough time and money hey could teach a horse to talk.
• Skinner also believed that the environment played a large role in development.
• Skinners "behaviorism" held sway in many parts of psychology for most of the mid-late 20^th century.
• Skinner trained animals to do such things as aim bombs, perform complicated tasks for food, and do show tricks.
• Although much of Skinner’s work is still misunderstood, his book "Walden Two" described a utopia where children could be trained to do any task.

PART 2: A BRIEF OVERVIEW OF GENETICS

• Each human has 23 chromosome pairs, for a total of 46 chromosomes.
• In each pair, one chromosome is inherited from the mother, and the other from the father, the 23^rd chromosome determines the sex of the child (XX, XY).
• Among the 23 pairs there are roughly 50,000 genes

• Monozygotic twins (MZ)- come from a single fertilized egg or zygote which then splits. MZ twins are often called identical twins because the share 100% of their genetic make up.
• Dizogotic twins (DZ)- come from two separately fertilized eggs. DZ twins are thus only 50% genetically similar.
• Full Siblings- Share the same mother and father, and have 50% of their genetic make up in common.
• Half Siblings- Share only one common parent and an only 25% genetically similar.

• Behavioral genetics are primarily concerned with the study of individual differences.
• Genotype- the combination of ones genes.
• Phenotype- The observed trait of interest.
• Examples- IQ, personality traits, physical traits.

• Heritability- The measure of genetic influences on individual phenotypic differences. It is the percentage of variance due to genetic factors.
• EG (high-height weight) (low-clothing style).
• Shared environment- the environmental influences on phenotype, which works to make family members similar. (E.g. social class, religion).
• Non shared environments- The environmental influences working upon each family member separately, causing differences among family members (e.g. peer groups, birth order).

• Passive- children receive genotypes correlated with their environment.
• Active- Individuals seek or create environments correlated with their genetic proclivity.
• Evocative- Individuals are reacted to on the basis of their genetic propensities.

• Separated twin design (IQ example, aggression example).
• Non-twin adoption studies (allows us to compare the genetic and environmental contributions in adoptive siblings).
• Classical twin design comparing MZ and DZ twins.

PART 3: THE ROLE OF PEERS - TWO NON-GENETIC PERSPECTIVES

• Research has indicated that child rearing can influence personality traits which can influence peer relations (Furman & Buhrmester, 1982; Putallaz & Hefflin, 1987).
• Modeling of parent relationships has also been used (Rubin & Sloman, 1984).
• Example Authoritative parents teach maturity and leadership.

• Emphasizes the role of peer groups in the socialization of the child.
• Harris argues that the peer group plays a larger role than the parents do in her book "The Nurture Assumption."
• Peer and environmental effects can also be seen in research on social learning theory (Bandura, and the Bobo doll example).

PART 4: COMMENTARY

• The third variable—genetic influences have not been taken into account. Genes may account for the make up of ones peer group (see evocative and active above).
• Genes can account for about 50% of the variance on personality tests while only 2-9% can be accounted by environmental influences.
• About 36% of the variance in popularity can be attributed to genetic influences (Rolf, Sells, & Golden, 1972).

• Twins are not always raised completely separated (Lewontin, Kamin, & Rose 1984). They could have been separated later in life, this creates confounds for the studies.
• Selective placement – Adoption agencies try to place children with families similar to their biological families. This could cause overestimation of genetic contributions to IQ.
• The lack of blame dilemma—This can be misused and people could just blame their genetics for failures, or criminal activity.

• The idea was posited first by Uri Bromfenbrenner.
• The theory indicates that children are born with certain genetic potentials (i.e. IQ), but the environment can the either cause the potentials to be realized or stifled (Scarr 1993)
• Example: Aggression and IQ (Rowe, Almeida, & Jacobson, 1999).

Further Readings:

Harris, J.R. (1998). The nurture assumption: Why children turn out the way they do. New York: Free Press.

Rowe, D.C. (1994). The limits of family influence. New York: Guilford.

Rowe, D.C., & Almeida, D.M, & Jacobson, K.C. (1999). School context and genetic influences on aggression in adolescence. Psychological Science, 10, 277-280.

Williams, W.M., & Plomin, R. (1999). Two views about the nurture assumption. Reviews of The nurture assumption, by J.R. Harris. Contemporary Psychology: APA Review of Books, 4, 267-271.

* On library reserve.