Nature versus nurture in human development

¶ … child psychiatry probably had its birth in 1899 Chicago, when social activists such as Jane Addams led the city to form the country's first juvenile court (Schowalter, 2003). Hull was dismayed by the juvenile delinquency she saw in the poor part of the city. The establishment of juvenile courts raised awareness regarding the number of youth with psychological problems, and experts started to study the issue in an attempt to determine its causes (Schowalter, 2003). Child guidance clinics opened across the country, with clinicians traveling to Europe to study with psychoanalysts such as Anna Freud and Melanie Klein (Schowalter, 2003). From the beginning, clinicians in this new field wondered whether nature, nurture, or some combination resulted in troubled youth. Skinner's behaviorism was popular for a while although it did not produce good results and faded in interest.

At some times experts believed that nature, or genetics, was the main determinant of mental health, while at other times most believed that a good upbringing -- nurture -- could head off most psychological problems (Schowalter, 2003). In various forms, the debate continues to this day, with some researchers finding that beliefs regarding whether nature or nurture is most formative for children vary according to the subculture the individuals live within (Schnittker et. al., 2000).

BOTH SIDES OFTHE DEBATE

Nature: Macindoe (2004) reviewed a book by David T. Lykkens that focuses on happiness and whether a tendency to be happy could be inherited. Macindoe reports that Lykkens looked at an extensive body of literature and concluded that "nearly every psychological trait or tendency that we can measure reliably owes part of its variation from person to genetic differences between people" (p. 3). While this is a remarkable finding, the fact that Lykkens used the phrase "part of its variation" is significant. According to Lykkens, genetics cannot explain everything about who we are (Macindoe, 2004).

Lykkens gives examples of behaviors that are clearly inherited in birds, such as babies instinctively pecking on the spot that will cause their parents to regurgitate food for them, but also demonstrates that birds have learned behavior that interacts with biology: baby birds raised in isolation, exposed to the sounds of many species. learn to mimic the song of their species, not another's, even though they have never been around their own species (Macindoe, 2004).

The influence of genetics on psychology has been particularly well document for bipolar disorder (Mota-Castillo & Auvil, 2004).

However, while it is clear that nature, through genetics, can add biological factors to the development of both positive and negative psychological traits, Lykken notes that the genes do not go so far as to constitute a blueprint for the person's mind and personality (Macindoe, 2004). The missing ingredient of course is the ability of the human brain to conceptualize, imagine, and think for itself. This introduces many variables into the human experience not present for most other animals.

Nurture: In his book on happiness, Lykkens argues that "skillful parenting can mitigate the effects of an excessively shy or inhibited temperament" (p. 22). The corollary to this would be that the wrong kind of parenting could make these traits worse. The real question is whether the environment can, by itself, cause significant psychological problems in children. Interestingly, Lykkens asserts in his book that, barring parental abuse or neglect, parenting style does not have much impact on adult personality. The main factors were genetics and environmental factors outside the family, such as friends and school experiences (Macindoe, 2004). Schnittker et. al. (2000) also found that the child's wider environment, including friends, school, and neighborhood, as well as the child's immediate family, influenced the effects of nurture on the child's development (Rutter, 2005).

Even in cases where high heritability has been established, such as bipolar disorder, the effect of nurture seems significant. Mota-Castillo & Auvil (2004) report a case where six out of six siblings all developed bipolar disorder. While it is possible that all six inherited the gene or genes for this disorder, it also seems likely to the researchers that nurture/environment played a role in the conditions' emergence in all six children (Mota-Castillo & Auvil, 2004).

Unfortunately, one way researchers know nurture can have a profound effect on a child's psychology is if the parents act in abusive ways, mistreating the children or depriving them in important ways (Bouchard, et. al., 1990). Nurture is hardly irrelevant, causing those involved with the placement of foster children to argue for trying to find stable, permanent homes in which the foster children can live throughout their childhood (Pietrantonio & Auvil, 2004).

Research on Twins: While human beings have many factors that can influence their behavior and mental health, we do have one avenue for research that can separate nature from nurture: identical twins who were adopted and raised in different homes. Differences between the two twins in a pair could reasonably attributed to nurture, while similarities would suggest genetic influence. The "Minnesota Study of Twins" was one of the most detailed explorations of nature vs. nurture. Researchers included 120 pares of twins raised in separate environments as well as four sets of triplets. In this study, the twins raised apart were markedly similar to their siblings even when raised in separate homes. They found from 25% to 80% off traits such as intelligence, musical ability and even degree of religious conviction could be explained by heritability (Macindoe, 2004). This means, of course, that from 20% - 75% of a person's attributes and talents cannot be explained by genetics. Nature and nurture work together to form the child and adult.

EXAMPLE of the INTERSECTION of NATURE and NURTURE

The example cited above where six out of six siblings all developed bipolar disorder (Mota-Castillo & Auvil, 2004) is a situation where some might explain the event as purely nature, while others might argue that the pattern suggests that nuture was the cause, since all six children exhibit similar and significant signs of psychological problems. The mother of the children reported a significant history of mental illness in her family and bipolar disorder was either identified as the diagnosis or a likely explanation in all those cases. In fact, the mother herself was diagnosed with bipolar disorder. Those who see nurture as the primary influence might argue that the children learned bipolar behavior from their mother and other relatives in the family who had the disorder. The researchers reported that a combination of medication therapy and family counseling allowed the children to function well enough to live a normal life, once more suggesting that both nurture and nature may play important roles in mental health (Mota-Castillo & Auvil, 2004).

THE MINNESOTA STUDY

The "Minnesota Twin Study" is one of the definitive pieces of research looking at the roles of nature and nurture in the development of personality and psychology of individual children. Begun in 1979, the researchers eventually included well over 100 sets of monoxygotic (identical, or MZA), and dizygotic (fraternal, or DZA) twins, and triplets, who were adopted separately and thus raised in individually unique environments (Bouchard, et. al., 1990). The researchers used rigorous methodology to determine whether twins were genetically MZA or DZA, since when this study began, genetic analysis was not available. The participants were thoroughly evaluated, including four personality trait inventories, three occupational interest inventories, and two different tests of mental ability. The environments in which they were raised were likewise thoroughly evaluated for comparison purposes (Bouchard, et. al., 1990).

Intelligence was looked at particularly closely, as the origin of intelligence has been closely contested in the nature vs. nurture debate. Using multiple measures of intelligence, the researchers found a high degree of correlation and determined that heritability accounted for 70% of the intelligence scores obtained. This was consistent with previous studies (Bouchard, et. al., 1990).

Then the researchers considered that even though the children were raised in differing environments, perhaps the environments were similar enough that they contributed to this trend. By carefully analyzing factors in the home, including intellectual stimulation, they found a low correlation between household similarities, suggesting that the environments differed in significant ways and did not contribute greatly to the strong trend toward two twins having similar IQ scores. Contact of the two twins with each other as they grew up, while it did occur sometimes, was also ruled out as a significant contributing factor (Bouchard, et. al., 1990).