Child Development From Infancy to Adolescence. Laura E. Levine
want to know which aspects of the environment influence the development of behavior so we can promote those environments associated with positive outcomes.
TRUE/FALSE VIDEO
T/F #8
Genetic inheritance plays a role in the development of almost all behaviors that have been studied. True
Studies of Identical Twins Reared Apart
The third type of study is a natural experiment, a type described in Chapter 2 that takes advantage of naturally occurring events researchers did not create or control to test a hypothesis. In this case, researchers studied identical twins who were adopted into separate families and measured how similar each was to his or her twin. If identical twins who are raised in different homes are more similar to each other on a certain characteristic than fraternal twins who are raised together in the same home, it suggests that genes are the stronger influence on the characteristic being studied.
The largest modern study of this unique population is the Minnesota Study of Twins Reared Apart (Segal, 2012). The Minnesota study began with the discovery of the “Jim twins,” Jim Lewis and Jim Springer. Although reared apart for 39 years, they showed startling similarities. Media coverage at that time focused on the anecdotal coincidences, such as their first marriages to women named Linda and second marriages to women named Betty, and their sons’ names (James Alan and James Allan), but the research team itself focused on a series of tests carried out with the Jim twins and subsequently with 81 pairs of identical twins and 56 pairs of fraternal twins. This research has indicated that identical twins reared apart are about as similar to each other on aspects of their personality, interests, and social attitudes as identical twins reared together, and more similar than fraternal twins reared together (Lehman, 2005; Segal, 2012).
T/F #9
Identical twins reared apart are more similar on many personality characteristics than nonidentical twins reared together. True
This research would appear to provide strong evidence for the powerful influence of genes on many characteristics, but there has been ongoing controversy about these findings. Joseph (2001) makes the case that many of these separated twins actually knew each other. Some were even adopted by relatives who lived in the same area, and some were raised together for a number of years before they were separated. That would mean that the environments for the twins were really very similar. However, Segal (2012) counters this argument by pointing out that the twin pairs in the Minnesota twins study were separated earlier and for a longer period of time than twins in previous studies and therefore provide better evidence of genetic input into a variety of characteristics.
Another criticism of this research raised by Joseph (2001) is that the similarities between twins might be due to similarities in age, sex, race, ethnicity, and level of attractiveness, because each of these characteristics is likely to make people similar to each other even when there is no genetic relationship between them. He suggested that the twins’ level of similarity should be compared to the similarity between pairs of unrelated strangers who have all of these characteristics in common. Although research that includes all of these characteristics has not been done to date, Segal (2013) did study people who were unrelated but looked alike to determine whether appearance elicits similar responses from others, which then would affect the personality and self-esteem of the individuals in these created pairs. She found that fraternal twins raised apart and raised together were much more similar to each other than unrelated look-alikes. (Remember that fraternal twins share half of their genes in common, while the unrelated look-alikes should not have any substantial number of genetic similarities.) From this, she concluded that the personality similarities found between identical twins in the Minnesota study are due to genes or possibly to other factors, but not to appearance.
Check your understanding of the use of concordance rates in twin studies by carrying out the activity in Active Learning: Concordance Rates.
Active Learning: Concordance Rates
Twin and adoption studies use concordance rates, the degree of similarity between two people on some characteristic, to assess the likelihood that genes influence the characteristic. Check your understanding of what concordance rates indicate by examining the following evidence and deciding what conclusions you would reach.
1 In a Danish population-based twin study of autism spectrum disorder (ASD), the following concordance rates were found for identical and for fraternal twins:If one identical twin was diagnosed with ASD, the likelihood was 95.2% that the other would also be diagnosed with ASD.If one fraternal twin was diagnosed with ASD, the likelihood was 4.3% that the other would also be diagnosed with ASD (Nordenbæk, Jørgensen, Kyvik, & Bilenberg, 2014).What would you conclude from this about the role of genes in the development of ASD?
2 In a study of types of emotional attachment to the mother, identical and fraternal 3-year-old twins were assessed to determine whether they had secure or insecure attachment.If one identical twin was securely attached, the likelihood that the other was securely attached was 70%.If one fraternal twin was securely attached, the likelihood that the other was securely attached was 64% (O’Connor & Croft, 2001).
From this, what would you conclude about the role of genes in the development of secure attachment?
Answers: 1. These findings indicate a strong role of genes in the development of ASD because twins with identical genes are more similar than twins with only half of their genes in common. 2. These findings indicate only a small or no role for genes in the development of secure attachment because twins with identical genes were only slightly more likely to be similar to each other in the quality of their attachment than those with only 50% of their genes in common.
Personality Characteristics and Genome-Wide Association Studies (GWAS)
Based on evidence from adoption and twin studies, researchers have searched for particular genes that are linked with the characteristics found to have high heritability. However, they had little success until the development of genome-wide association tests, described earlier in this chapter, that allowed them to look at the whole human genome without having to guess beforehand which specific genes to examine (Amin et al., 2013). In recent years they have had success in locating areas of the genome and combinations of genes that are linked with what have been called the big five personality characteristics: extraversion, conscientiousness, agreeableness, neuroticism, and openness (Amin et al., 2013; de Moor et al., 2015; van den Berg et al., 2016). However, as you will see in the next section, the presence of specific genes does not necessarily determine someone’s behavior. Experiences in the environment can affect how genes are expressed.
Check Your Understanding
Knowledge Questions
1 Why do genetics researchers study adopted children?
2 What does a concordance rate measure?
3 What could explain some of the striking similarities reported between identical twins separated at birth?
Critical Thinking
Think of a behavior or nonphysical trait that you share with one of your parents. Can you remember being taught to behave that way or trying to imitate your parent while you were growing up? If not, do you think you inherited this behavior genetically? Why or why not?
The Interaction of Genes and Environment
>> LQ 3.5 How do genes and the environment interact?
We have now seen how genes work within our bodies at the molecular level, and we have looked at the ways in which