Nature vs. Nurture: Genetics and Environment in Human Development

Introduction

Upon researching the issue of nature vs. nurture and both elements' direct influence upon human development, it is clear that there is no definitive way to argue whether one plays a greater role than the other. Upon further reflection, it is only fair to propose that both play a significant role in human development and in shaping a person's character. At this point in our understanding, it is safe to note that a number of different factors come into play given the complexity of human society. The discussion below establishes a strong argument for equal influence in one's development. However, one important detail must be noted: throughout human development, there are periods in which one factor may carry greater emphasis than the other depending on the stage. There are times in life where nurture will be more important and nature will take a back seat, and vice versa.

The nature vs. nurture debate has been a classic controversy among experts for centuries. Presently, there is no clear conclusion to the dispute; yet, many hypotheses have been proposed. Both sides of this controversy have been thoroughly explored by researchers. The purpose of this paper is to argue that the mental aptitude of a person is determined by genetics as well as by environment, and to examine which of the two affects intelligence more.

The Role of Nature: Genetics and Heredity

The nature side of the discussion argues that a person's mental ability is determined solely by what he or she is born with genetically. Defending this side of the debate exclusively would mean establishing that a person's environment plays no role in determining intelligence. There are many reasons an individual might be convinced that genes play a large part in intelligence. When considering genetics, it is clear that genes provide humans with their physical foundation for life. Genes and chromosomes are passed from each generation to the next; without heredity, humans would have nothing to pass on biologically to their descendants. This idea that genetics is purposeless is clearly incorrect. For instance, when genes are exposed to a particular environment — such as the area surrounding Chernobyl — their blueprint can change: many infants exposed to that environment have developed cancer.

Twin studies are conducted on sets of twins, including both identical twins and fraternal twins, to determine the comparative influence of heritability and environment (Morris and Maisto 82). "These studies determine the heritability of a trait: to what extent the differences among individuals are due to genes, rather than to environmental factors such as upbringing, nutrition, and schooling" (Wright). "Recent twin research showed that the genetic contribution to happiness and stability are about 50% and 80%, respectively, while life events have only a transitory effect on happiness" (Segal 55). Segal's finding is not directly about human intelligence; yet, if his statement is true, it substantiates the importance of heredity. It indicates that heredity does have a notable effect on a person. In general, twin studies offer more support for the nature side of the debate (Morris and Maisto 82).

Adoption studies are somewhat similar to twin studies in that they are conducted for related reasons. These studies consist of monitoring and testing adopted children, their birth parents, and their adoptive parents, comparing IQ scores across these groups. Some of these studies have shown that heritability accounts for approximately 48% of the variance in intelligence among most humans (Hamer and Copeland 219).

The Role of Nurture: Environment and Development

On the other hand, many investigations have shown that a person's environment plays a large role in his or her intelligence. Although this may be the less immediately obvious influential factor, the enormous impact of a person's surroundings warrants careful examination.

The amount of nourishment an individual receives has been proven to play a very large part in mental ability. This is especially true for infants and young children. The human brain critically needs nutritious food and antitoxins to function properly, particularly in the earlier years of development. Starvation across the globe demonstrates why a lack of nutrients can stunt mental development as well as physical growth. "What a premature infant eats in the first month of life can have lasting intellectual impact ... A new study finds" (Raloff).

A study conducted in Great Britain in the late 1980s further illustrates how nutrition factors into cognitive development. Adolescents aged twelve to thirteen were given vitamin and mineral supplements for eight months and then administered intelligence tests. Their scores were compared to those of adolescents who did not receive supplements. The students who took the supplements scored higher on the tests afterward (Herrnstein and Murray 292).

A person's environment also plays an important role in development during the first three years of life. Much research shows that people benefit greatly from early stimulation. In an experiment conducted by H.M. Skeels using orphans, this concept was demonstrated clearly. Skeels studied mentally disabled orphans and found that once these children were placed with caring families and were encouragingly nurtured, their IQs increased remarkably (Hamer and Copeland 221).

Other studies support this evidence. Kagan and Havemann define operant conditioning as the process by which, through learning, free operant behavior becomes attached to a specific stimulus (578). John Watson conducted a substantial experiment in 1913 concerning behaviorism. He became well-known as the psychologist who played a large role in the research of behaviorism, which is a division of operant conditioning. Watson used an 11-month-old boy to prove that a person could be conditioned to fear something by which he was not previously affected. The baby, Albert, was placed in a room alone with no distractions. Watson introduced a white rat into the room; Albert appeared to like the rat and even showed affection toward it. Subsequently, Watson produced a very loud and unpleasant noise every time Albert reached out to touch the rat. As a result, the baby became terrified of every white and furry object he encountered. This distinguished investigation became known as the "Albert experiment" (Kagan and Havemann 94). It established that humans could be taught certain feelings and fears through their environment — responses with which they were not born (Morris and Maisto 15). Experiments such as these prove that a person's environment can have a crucial effect on his or her manner of thinking and attitude.

Conclusion

Both nature and nurture affect a person considerably; although, the research reviewed here favors environment as having more influence on an individual. This debate, like most, is very inconclusive and ongoing. It is up to each individual to decide where he or she stands. The mental ability of humans is partly determined by genetic makeup, but there is also substantial evidence that environment affects mental aptitude significantly. Through a review of the available research, one can conclude that environment has more overall impact, given the breadth and consistency of evidence supporting that view.

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