- Read the following English statement and answer the questions
Behavior Genetics: Explaining Individual Differences
While evolutionary psychologists explore the behavioral implications of Darwin's big idea in hopes of explaining our universal human tendencies, behavior geneticists explore our differences from one another. How much are we shaped by our genetic blueprint? By our upbringing? By our culture and current circumstances? By how our environment reacts to our genetic traits?
To answer such questions, behavior geneticists harness powerful methods such as twin studies. To discern the effect of heredity, it would be nice if we could hold shared environment constant while varying heredity. Happily for our purposes, nature has given us ready-made subjects for this experiment: identical versus fraternal twins. Identical twins, who develop from a single fertilized egg that splits in two, are genetically identical (Figure 2.26). They are?millions and millions of them?nature's own human clones. (The possibility of laboratory human cloning raises new ethical issues but hardly new psychological issues.)
Fraternal twins, who develop from separate eggs, are genetically no more similar than ordinary brothers and sisters. A person whose identical twin had Alzheimer's disease has a 60 percent risk of sharing the disease; with an affected fraternal twin, the risk is 30 percent (Plomin & others, 1997). Such a difference suggests a genetic influence. Behavior geneticists ask: Are identical twins, being genetic clones of one another, more similar than fraternal twins? Studies of nearly 13,000 pairs of Swedish identical and fraternal twins, of 7000 Finnish twin pairs, and of 3810 Australian twin pairs provide a consistent answer: On both extraversion (outgoingness) and neuroticism (emotional instability), identical twins are much more similar than fraternal twins. Genes matter.
Other dimensions of personality also reflect genetic influences. John Loehlin and Robert Nichols (1976) gave a battery of questionnaires to 850 U.S. twin pairs. Once again, identical twins were much more similar, and in a variety of ways, in abilities, personality, even interests. However, the identical twins, more than fraternal twins, also reported being treated alike. So, did their experience rather than their genes account for their similarity? No, said Loehlin and Nichols. Identical twins whose parents treated them alike were not psychologically more alike than identical twins who were treated less similarly.
Fraternal twins, who develop from separate eggs, are genetically no more similar than ordinary brothers and sisters.
Identical twins whose parents treated them alike were not psychologically more alike than identical twins who were treated less similarly.