Feral children provide another opportunity to study the nature/nurture issue. Typically, the cases of feral children get much more attention than the normal, more scientific methods of researchers. Feral children are children who appear to grow up in the wild or to be brought up by animals. These children seem to have had very little, or no, human contact while they were growing up. Feral children would seem to support the conclusion that experiences (i.e., nurture) are important to the normal development of the human brain. If these children experienced deprived environments in their youth, then these deficient environments led to them developing very poorly and with many cognitive deficits compared to normal human children. As promising for studying the nature/nurture issue as these cases might seem to be, they are few and far between, so they amount to nothing more than case studies that capture a lot of attention. Candland (1993) discusses the stories of many feral children such as Peter, Victor (the Wild Boy of Aveyron), and the wolf-girls of India. In the end, however, real-life examples of feral children have too many unanswered questions to provide accurate information concerning the nature/nurture debate. For instance, exactly where and when were these children abandoned, and exactly why were these children abandoned? It may be that these children were severely disabled to begin with and this may be the very reason that they were abandoned in the first place. If this is so, then these children really do not provide unique information about the nature/nurture issue. As is usually the case with real-world examples, the number of uncontrolled factors is so numerous that no conclusive data can be obtained from the reported cases of feral children. Nonetheless, these cases will continue to garner a large amount of attention, and they provide a more human face and emotional connection to the nature/ nurture debate.
In psychology today, researchers have a number of methods that help them to identify the extent to which nature and nurture influence psychological traits. First, twin studies involve the comparison of identical and fraternal twins. Identical twins develop from the same fertilized egg, so they are called monozygotic (MZ) twins. Identical twins have the same genetic makeup, so their genetic relatedness is 100 percent. Thus, any differences found between identical twins can be attributed to the environment (i.e., nurture). Fraternal twins, on the other hand, develop from two separate fertilized eggs, so they are referred to as dizygotic (DZ) twins. Fraternal twins are like any two siblings with a genetic relatedness of 50 percent. This difference between identical and fraternal twins in genetic relatedness is key to drawing conclusions about nature and nurture from twin studies. With this basic knowledge of genetic relatedness of twins one can make conclusions based on correlations between twins on a particular psychological trait. If a trait is influenced by nature (heredity), then researchers should find that fraternal twins are more variable (or different) on that trait as compared to identical twins. Because identical twins have the exact same genetic input, researchers should not observe any differences between them on a trait that is hereditary in nature. However, if a particular trait is not influenced by nature, then researchers should find that identical twins are not any more similar to each other on that trait than fraternal twins are to each other (Dunn & Plomin, 1990; Plomin, 1990). Another method that researchers use to study the influence of nature and nurture on psychological traits is adoption studies. Some adoption studies examine individuals who are not genetically related to one another, however they all live in the same environment (i.e., family). Other adoption studies examine individuals who are genetically related to one another, but they are raised in different environments. If nature is a key component for a trait, then individuals who are genetically related to one another (irrespective of their environments) should be similar on that trait. However, if nurture is a key component of a trait, then individuals who share a particular environment should be similar on that trait (irrespective of their genetic relatedness; Dunn & Plomin, 1990).
Every person in this world has their own distinctive personality and behavior. People may wonder why an individual may act the way they do. Thus psychologists had put this into a study of whether an individual’s behaviors are caused by hereditary or the environment. This study is known as the nature-nurture debate. This essay will discuss the nature-nurture debate in relation to how it influences the human traits and behavior focusing on twin and adoption studies. Furthermore the essay will also discuss how hereditary and the environment influences on the behavior of intelligence base on twin and adoption studies.
“The nature-nurture issue is a perennial one that has resurfaced in current psychiatry as a series of debates on the role that genes (DNA) and environments play in the etiology and pathophysiology of mental disorders” (Schaffner) The debate is essentially about what is inherited (nature) and what is experienced by environmental factors (nurture) and how they affect human development.
The debate of nature versus nurture had been dated back to the time of Greek philosophers like Plato and Aristotle (Crooks & Stein, 1991). In this context, according to Feldman (1997), nature means the genetic influence on the individual’s behavior. In relation to that, nurture means the effect the environment has on that individual, for example influence of parents or friends. The purpose of the nature-nurture debate is to explain the effect of genetic influence and the environment on the development of human trait and behavior (Crooks & Stein, 1991).
Research investigating the nature and nurture issue in a variety of areas (e.g., intelligence, personality, mental illness, etc.) has potential applications. Knowledge about the causes for mental illnesses, for instance, directly affects the treatment that professionals will use for people suffering from those illnesses. For example, the discovery of substantial heritability rates for some mental illnesses, such as bipolar disorder, supports the continuing medical search for biological treatments, such as drugs. Furthermore, knowledge concerning exactly what parts of the environment influence mental illness can help psychologists to develop more targeted psychological treatments. In addition, the extent to which researchers believe that intelligence and personality are influenced by the environment can help to determine educational approaches from preschool through college.
The debate concerning the heritability of intelligence is one example of a continuing issue, and a vigorous one at that, in the nature versus nurture debate. Providing viewpoints from both sides of the debate demonstrates some of the complexities that will continue to keep this debate an important part of psychology over the next century. Although some still argue that either nature or nurture is the most important influence on human beings and their psychological traits, the future seems to be focused on interactionist approaches that will attempt to better explain how nature and nurture interact to make us who we are psychologically.
Although psychology in the 21st century is a scientific field that has developed many methods to investigate psychological phenomena, and our understanding of development has become more sophisticated, the nature versus nurture debate remains very active. An example of part of this continuing debate that will exist for the foreseeable future is the heritability of intelligence. Since Galton and Goddard argued that intelligence is essentially inherited, there have been researchers who have supported this conclusion. Over the years aspects of this debate have become part of the more unseemly beliefs of racism. Not that those who conclude that intelligence is inherited are racist, but that conclusion has in the past been partly motivated by racist beliefs against immigrants. This should demonstrate how volatile the nature versus nurture debate can be and how potentially important and influential research findings in this area are. In 1994 Herrnstein and Murray argued that intelligence was indeed a general cognitive ability on which humans differ, that IQ scores do not fluctuate much over the life span, and most importantly, that intelligence is largely heritable. Although behavioral genetic research tends to support the conclusion that intelligence is indeed substantially influenced by nature, most researchers today emphasize an interactionist perspective that recognizes the importance of both nature and nurture even when perhaps a majority of a trait, like intelligence, might be attributable to nature.
Even though the focus of most psychologists today is on the interaction of nature and nurture, there are still some theoretical approaches that emphasize the importance of nurture. Ericsson, Nandagopal, and Roring (2005) argue for the nurture side of the debate. They argue that expert performance does not rely on an inherited talent or giftedness; rather, expert performance is the result of acquired abilities that have been developed through extended deliberate practice. Ericsson et al. (2005) argue that evidence supports the conclusion that, contrary to experts in a given domain being born, before one can perform expertly in a given domain he or she must have prolonged experience in that field. Furthermore, they point out that a person’s performance in a specific area improves gradually over time and with experience; even the performance of so-called child prodigies follows this pattern. Ericsson et al. also argue that the historical improvements in performance over the last 100 years support the conclusion that expert performance is not due to innate talent. They point out that if talent were genetic, then improvements in talent over the last 100 years would not be possible because genes would fix an upper limit on talent that could not change dramatically in so short a time period. So according to Ericsson et al., their expert-performance framework attributes differences in expert performance (even among so-called prodigies) to acquired cognitive and physiological changes that are the result of extended deliberate practice.
Although the field of behavioral genetics has demonstrated the importance of heritability to a plethora of psychological traits, the same findings also lead to the conclusion that environment too plays an important part in these psychological phenomena. Even though research findings concerning how much of a trait like intelligence is due to our genes is often widely disseminated in the media, the other side of the coin is nurture. Any variance that is not due to genes is by definition due to environment (Steen, 1996). Nature never accounts for 100 percent of the variance for any psychological trait. Instead, psychological traits are most likely the result of a number of interacting genes that account for a large part of the variance for a particular trait. However, the remaining variance that is due to environment remains important. So, if 47 percent of the variance for the trait of extroversion is attributable to genes, then that means that 53 percent of the variance for extroversion is due to the environment. Perhaps environmental factors are not discussed as often in the media because there are many possible environmental factors that can be involved, ranging from parenting style to culture to a viral infection.