Nature Versus Nurture Research Paper

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Abstract

One of the most persistent issues in the field of psychology is the nature versus nurture debate. This debate concerns how much of an individual, and who s/he is, can be attributed either to nature (i.e., inborn tendencies or genetic factors) or to nurture (i.e., learning or environmental factors). This debate can be one of the most contentious issues in psychology because of the potential serious political ramifications of nature/nurture findings (de Waal, 1999). Although the science of psychology has entered the 21st century, it seems that the nature versus nurture debate will continue to be an active part of psychological research for many areas, including research on intelligence, personality, and mental illness. This research paper will begin with a general overview of the history of the nature/nurture question, focusing on the history of psychology and how psychologists have emphasized the different sides of this debate over time. Next, I discuss current approaches in psychology relevant to the nature/nurture debate and possibly the most controversial aspect of this debate today (i.e., the heritability of intelligence). In addition, the research methods that psychologists have at their disposal to help them determine whether a trait has genetic or environmental influences will be described. Lastly, I discuss the complexities of trying to apply research from the nature versus nurture debate.

Introduction

The nature versus nurture debate stretches all the way back to the earliest days of Western philosophy, when Plato essentially believed that knowledge was inborn in humans and we merely needed to recollect this knowledge (although Plato did not believe that this was necessarily an easy process). We can firmly place Plato’s position on the nature side of the debate. On the other hand, we can firmly place another major figure in Western philosophy, Aristotle, on the nurture side of the debate. According to Aristotle, true knowledge was not inborn but came from one’s experiences with and observations of the physical world. This debate has been reincarnated repeatedly throughout the history of Western civilization. For instance, many centuries after Plato and Aristotle, the German rationalist Emanuel Kant and the British empiricist John Locke were laying out positions on opposite sides of this same debate. Of course, it was Locke who popularized the notion of the human mind as a tabula rasa (blank slate) at birth, meaning that individuals are not born with innate knowledge; rather, any knowledge or ability that a person eventually attains will have come about through that individual’s experiences. This places Locke firmly on the nurture side of the debate. On the nature side of the debate was Kant. Kant believed that before the mind could make any sense of its experiences there had to be an innate structure to the mind that enabled it to perceive the world and give meaning to one’s experiences. It was this innate ability of the mind that was most important to the attainment of knowledge. Whereas Plato, Aristotle, Locke, and Kant were primarily concerned with how humans can gain knowledge, modern psychologists are more interested in factors such as intelligence, personality, and mental illness. Thus, the nature versus nurture debate has a long history in Western culture (Hergenhahn, 2005). This research paper, however, will focus on the nature versus nurture question in psychology.

Since the early days of modern, scientific one area that has consistently been intertwined with the nature/nurture issue is intelligence. Some of the early leaders in this area of psychology such as Galton and Goddard believed that intelligence was largely inherited. At the time, the Zeitgeist (i.e., spirit of the times) emphasized evolutionary theory. So scientists like Galton tended to have a strong bias toward the nature side of the debate. This bias was manifested in Galton’s explanation of his data. Although Galton was the first to conduct twin studies, which continue to be important in the nature/nurture debate, and to study families over time, his bias toward nature led him to underestimate the influence of the environment. When Galton discovered that achievement tends to run in families he concluded that this was evidence that intelligence was inherited. In America, Goddard shared Galton’s view of intelligence. Goddard’s famous “Kallikak” family study traced two lines of a family back to the American Revolutionary War period. Goddard believed that he had identified two sides of a family. One side was intelligent and responsible, whereas the other side was unintelligent and had criminal inclinations. These two sides of the family supposedly began with two different women, one of whom was intelligent and the other feebleminded. So, Goddard interpreted the “Kallikak” family history as supporting the conclusion that intelligence was inherited. Like Galton, Goddard failed to consider important possible environmental factors that can also influence psychological phenomena. Unfortunately, the belief that intelligence was inherited, along with the Zeitgeist of applying evolutionary theory to virtually everything, led to some of the most controversial applications in the history of psychology. Galton, for instance, was a strong supporter of eugenics (selective breeding for humans), and he believed that the government should match intelligent people and pay for the education of their children. Even more controversial are some of the policies that Goddard and other psychologists supported, such as the forced sterilization of feebleminded people and dramatically lowering the number of immigrants accepted into America for fear of too many feebleminded people arriving and having too many unintelligent children (Hergenhahn, 2005). Fortunately, this strict view of intelligence’s being inherited and not influenced by the environment would not persist forever.

In the early 20th century a new school of thought in psychology began to dominate the discipline, and this approach swung the pendulum all the way to the opposite end of the debate. Behaviorism emphasized the role of nurture and the environment in influencing individuals and their behavior. John Watson, the founder of behaviorism in America, denied that there were any inherited influences on human behavior. Instead, Watson made the bold claim that if he were given infants, then he could make one a doctor, another a thief, another a painter, and so on. He would merely need to control and manipulate the environment in which an individual developed. Any hereditary factors were unimportant and irrelevant to the development of the individual. So psychology passed into a period when there was a strong bias toward the nurture side of the debate (Hergenhahn, 2005). This emphasis on the environment was so strong that many psychologists believed that a phenomenon like the infant-mother bond was not in any way related to nature. Instead, it was argued that the infant-mother bond developed as a result of the mother (a neutral stimulus) being paired with primary reinforcers (e.g., food, milk, etc.).

Harlow challenged this assumption that the infant-mother bond was due only to nurture (i.e., learning). Harlow (1958) raised infant monkeys with two surrogate mothers. One surrogate mother had a body composed of wire mesh. This wire mesh mother provided the milk to the infant monkey. The second surrogate mother did not provide any food, but its body was covered with a soft terry cloth. Harlow found that the infant monkeys clung to the terry-cloth-covered mother, not to the wire mesh mother that provided the milk. This finding contradicted the behaviorist assumption that the reason for the mother-infant bond was that the mother became associated with food (i.e., the mother essentially becomes a secondary reinforcer). Instead, Harlow’s (1958) research suggested that there was a biological need for “contact comfort” (p. 676) that had more influence on the mother-infant bond. In addition to Harlow’s study, there was additional research that was demonstrating that the behaviorists had gone too far when they concluded that nature did not need to be considered in the development of the organism (Hergenhahn & Olson, 2005). Research by Marian and Keller Breland, for instance, identified the phenomenon of instinctual drift where an instinct would displace an earlier learned behavior, so that a behavior that was initially brought about by the environment was displaced by the biological instinct of the organism (Hergenhahn & Olson, 2005). In addition, other research on the Garcia effect, or conditioned taste aversion, found that the biology of the organism did indeed need to be considered in learning and in the wider field of psychology. This trend toward a recognition of the biological factors that can influence the behavior of the individual continued and eventually led to the development of evolutionary psychology. In evolutionary psychology, researchers focus on the biological design of the organism and on how certain behaviors developed over time because they were adaptive (enabling the organism to survive long enough in a particular environment to have offspring, and also enabling an organism to assist those she or he is biologically related to and so also pass genes into the future in that way). As biological influences on behavior and cognition became more and more evident, the field of behavioral genetics developed. Behavioral genetics is the field of psychobiology that examines all the genetic factors that impact on behavior and cognition (Hergenhahn, 2005).

Current Psychological Approaches On Nature Versus Nurture

Today there are a number of approaches that are relevant to the nature/nurture issue in psychology. The first of those areas is behavioral genetics, which has grown into a very respectable and popular area of study. Behavioral genetics focuses on identifying the heritability of psychological traits, such as intelligence and personality. Heritability is “an estimate of the size of the genetic effect” (Dunn & Plomin, 1990, p. 32) for a particular trait. Twin and adoption studies are among the methods that behavioral geneticists use to determine heritability. These methods will be discussed in more detail later in this research-paper.

The field of behavioral genetics has been able to conclusively demonstrate the importance of nature on many psychological traits. For instance, estimates for the heritability of intelligence range from 0.50 to 0.80 (Hergenhahn, 2005). This means that genetic factors account for 50 to 80 percent of the variance for intelligence. The heritability of manic depression (bipolar affective disorder) is around 67 percent; for depression, 60 percent; and for schizophrenia, 79 per-cent (Steen, 1996). In addition, estimates for the heritability of various personality traits are 47 percent for extroversion, 46 percent for openness, 46 percent for neuroticism, 40 percent for conscientiousness, and 39 percent for agreeable-ness (Steen, 1996). So, research has determined that nature is indeed an important determiner of who we are.

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.

In the past, the part of the environment that has perhaps been assumed as having the most influence on psychological traits is the shared family environment. Much past research has compared children from different families to one another, assuming that all the children from one family must all experience the same family environment (Dunn & Plomin, 1990). Behavioral geneticists, however, have found that the shared family environment has little effect on personality traits. The amount of variance for personality traits that can be accounted for by the shared family environment is around 5 percent (Hergenhahn, 2005). Dunn and Plomin (1990) point out that anecdotally the differences between siblings exceed the similarities, as most people with brothers and sisters can attest. Indeed, the correlations between siblings for a variety of traits are astonishingly low. A correlation of 0.50 between siblings would mean that they “are different and similar in about equal measure” (Dunn & Plomin, 1990, p. 10). If the correlation were higher than 0.50, then the siblings would be more similar to one another than different. However, if the correlation were lower than 0.50, then the siblings would be more different from one another than similar to one another. The correlations between siblings for many personality traits are very low (e.g., extraversion is 0.25 and neuroticism is 0.07). These low correlations support the conclusion that shared family environment, long the focus of many studies of nurture’s influence, is not a key determiner of psychological traits. Because siblings differ so substantially from one another, it makes sense that any part of the family environment that they experience similarly to one another is not relevant to these differences. Instead, it is those aspects of the family environment that are experienced differently that are more relevant to the development of psychological traits (Dunn & Plomin, 1990). So, one focus of recent studies on the influence of environment has been on nonshared environmental factors. Most likely, this will remain a focus for studies of the environment and how it influences psychological traits well into the 21st century.

With behavioral geneticists demonstrating the importance of both genes and the environment on psychological traits, theoretical approaches are beginning to focus on explaining how nature and nurture interact. More barriers between subfields in psychology and between disciplines are being broken down, resulting in more integrated and interactionist models of development (de Waal, 1999). Dai and Coleman (2005), for instance, state that a monistic view of giftedness as being the sole result of nature is no longer a supportable position. An example of a more interactionist perspective is a multiplier effect, which refers to how a single, small factor may ultimately have a large effect on a trait or talent because that small factor interacts with and creates a chain of reactions that multiply over time into the ultimate output for the giftedness (Papierno, Ceci, Makel, & Williams, 2005). So, very small changes in an individual’s genetic makeup (consisting of one gene being present or absent, or perhaps consisting of a number of genes each only contributing a small percentage of variance), an individual’s environment (such as having a brother vs. a sister), or an individual’s culture (such as being raised in a collectivist vs. individualistic culture) can be the impetus that sets into motion a set of reciprocal interactions that ultimately results in the individual developing into a gifted person capable of successfully composing touching and enjoyable music. These multiplier effects are key components of bioecological models of human development. Bioecological models have come to recognize how genes and environment can create feedback loops in which they push a particular trait to develop further and further. The ultimate example of this would be what is called the Matthew Effect. The Matthew Effect essentially states “that initial advantage begets future advantage” (Papierno et al., 2005). For instance, perhaps a child has an initial genetic advantage in verbal ability, so the child talks more to her parents. The parents, of course, notice and respond to this by reading more to the child and reinforcing a wider variety of verbal responses from the child. This leads to the child having better verbal ability when she begins school, and so on. This continues until she one day writes the great American novel of the 21st century, or that is the possibility.

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 gifted-ness; 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 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.

There are a number of important criticisms of the conclusion that intelligence is inherited. These criticisms can also be applied to many other traits and the belief that they are largely inherited. First, just because a test for a particular trait such as intelligence has been developed, that does not mean that the trait actually exists as an independent construct. Hanson (1996) argues, “When a given test becomes sufficiently important, whatever that test tests gets reified as a single quality of thing” (p. 112). Although intelligence tests have existed for over 100 years, it is tempting to assume that intelligence as an objective phenomenon does exist; however, critics warn not to reify a psychological trait just because we have named it and developed tests to measure it. So, if we cannot be sure of its objective existence, then how can we conclude that it is heritable? Another equally important criticism concerns disagreements over how to define intelligence. Intelligence tests that are currently in widespread use do not attempt to measure every kind of intelligence that has been proposed (Gardner, 1996). Intelligence tests measure only what they are designed to measure. Furthermore, any test is an indirect and inaccurate measure that is constantly being changed to measure the trait more accurately (Hanson, 1996). So, if researchers disagree on how to define intelligence and if intelligence tests keep changing over time, how can we conclude that intelligence is heritable? One last criticism of the conclusion that intelligence is heritable concerns the fact that heritability is a descriptive statistic of the amount of variance that can be attributed to genes for a particular trait in a specific sample of individuals. Descriptive statistics are used to describe a specific group of individuals. It is not appropriate to generalize descriptive statistics for one sample to other people. Thus, critiques point out that you cannot identify how much of a particular trait is genetic in one group of people and assume that this will be the same in other people everywhere.

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.

Methods

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 com-pared 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).

Researchers can use twin and adoption studies to estimate the heritability of traits. It should be made clear that heritability is a descriptive statistic that estimates the size of a genetic effect for a particular trait in a specific group of people. So, heritability merely describes a genetic effect for individuals in a particular study. Heritability is not “an immutable constant” (Dunn & Plomin, 1990, p. 33) that researchers can generalize to all people (Steen, 1996).

Instead, heritability estimates the effect size for genetics in a particular group, at a particular time, and even in a particular environment. So when researchers identify the heritability of a trait, that does not mean that that same heritability will necessarily apply for that trait in other people (Dunn & Plomin, 1990).

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.

Yet another naturally occurring phenomenon that garners much attention, and on the surface seems ideal for studying the influence of nature versus nurture, is the existence of savants. The term savant is used to refer to those who have an outstanding ability in one area or skill while simultaneously having a more general intellectual deficiency (Miller, 2005). Researchers and theorists have used the existence of a unique and an especially astute ability in a specific area as one part of the evidence for specific or multiple intelligences (Gardner, 1983). Because this one ability is intact, yet other abilities are not, it suggests that there are specific innate abilities for this sort of “intelligence” that the savant displays. On the other hand, some argue that savants may focus all of their attention on one ability or skill and develop it through practice (Miller, 2005). So again the complications of naturally occurring phenomena block researchers from making firm conclusions regarding nature versus nurture from savants.

Research that will help to investigate the different influences of nonshared environments deserves consideration. These studies should focus on studying multiple individuals who are raised in the same family. This approach will allow researchers to begin to understand how each child in a family has a unique environmental experience. Not only will different children in the same family have nonshared environmental experiences, but each child may be differentially affected by the same environmental stimulus such as mom or dad (Dunn & Plomin, 1990). Examining these nonshared environmental factors and how different children in the same family experience the same environmental stimulus differentially will require detailed study over an extended period of time, including having parents and siblings answer detailed questionnaires concerning their childhood and current psychological traits. In addition, researchers need to conduct longitudinal studies following children throughout their childhood and into adulthood to identify and understand these developmental processes.

Psychology has developed many useful research methods to study nature versus nurture, including twin studies and adoption studies. Psychologists have also been able to study some naturally occurring phenomena, such as feral children and savants, to help understand the influences of nature and nurture. Future studies will likely focus more on nonshared environmental factors. In addition, as medical technology becomes more and more sophisticated and as researchers are able to identify specific genes that influence psychological traits, researchers will be able to test individuals for the presence of these genes and determine just how much a particular gene might influence the development of something like schizophrenia.

Applications

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.

One potential danger in applications from research on nature versus nurture concerns concluding that nurture is the primary influence on development, thus leading to the erroneous conclusion, once held by the behaviorists, that biology and basic human needs do not need to be considered when designing or implementing educational or other service programs. A more detailed discussion and critique of denying nature’s influence on human beings is provided by Pinker (2002). Pinker discusses the historical influence of the notion of the human mind as a blank slate and how that can lead to a plethora of problems when trying to design and implement social service programs and create public policy.

On the opposite side of the debate, another danger is prematurely attributing the majority of a particular trait to nature or genes. Especially if researchers determine that a “deficiency” is attributable to genetics, then the temptation is to assume that nurture (or the environment) cannot influence it, and therefore there is a temptation to make no attempt to improve that person’s lot in life (Candland, 1993). Even if the majority of a trait is due to nature we make a mistake to assume that nature and nurture are mutually exclusive (Candland, 1993). Instead, even if the majority of a trait might be attributable to genes, some of the trait is still attributable to nurture. Furthermore, genes and the environment always interact in their expression. Genotype refers to an organism’s genetic makeup, whereas phenotype refers to an organism’s actual attributes and characteristics (Burdon, 1999). So, a person’s genes might set the range for how tall a person will be (say from 5 feet 5 inches to 6 feet 5 inches), but the environment in which a person grows up will determine where in that range the person develops. So, if individuals live in a restricted nutritional environment, they will develop at the lower part of the range, and if they develop in a nutritionally rich environment, they will develop to the higher end of the range and be taller. So, any genotype (no matter how strong) interacts with the environment to manifest a final phenotype in the individual. If this is true for a simple trait like height, then how much more so will more complicated traits, such as intelligence (whose genetic component is likely due to an interacting cluster of genes), be influenced by the environment? Therefore, when applying research from the influence of nature on psychological traits, policy makers should keep in mind that no matter how much of a trait is attributable to genetics, nurture always plays a role in the final expression of that trait. Therefore, researchers always must take nurture seriously as an interacting factor that contributes to our development and psychological characteristics. Furthermore, policy makers must remember that science (including psychology) is a field of study that attempts to provide more and more accurate knowledge over time. So, current conclusions regarding the influence of nature and nurture will change over time as our knowledge gets better. This means that applications should also be changed as scientific knowledge improves; hence, policy makers need to remain knowledgeable concerning the constantly changing conclusions in the nature versus nurture debate.

Summary

The nature versus nurture debate has a long history in Western philosophy and modern psychology. The debate is relevant to many different areas of study in psychology, including intelligence, giftedness, sexual orientation, personality, and mental illness. Today, most psychologists take an interactionist approach that views both nature and nurture as being important in development. However, some researchers still emphasize either nature or nurture as being the key component that determines a psychological trait. Many psychological researchers will continue to use tried-and-true research methods such as twin and adoption studies to examine the nature/nurture issue; however, future genetic research will identify more genes that influence behavioral and psychological phenomena. Future research on environ-mental factors will focus on the importance of nonshared environments and how different children in the same family might experience the same environmental stimulus in different ways, thus having a very different influence on their development. Research findings regarding nature and nurture will continue to be among the most applicable aspects of psychological studies, but they will likely also remain among the most politically volatile issues in the field.

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