Nature vs. Nurture Debate in regard to Intelligence.

The great nature versus nurture debate has recently shifted from, whether our genetics or the environment influences our psychological processes, to how much both, biology or the environment has an impact. Both nature and nurture have been researched thoroughly with evidence to support both sides of the debate. The nature side or the genetic side argues that intelligence is inherited in the way that a person is born with their maximum mental ability. To say that a person’s genetics solely established their mentality is to say that the environment has no influence at all. On the other hand the nurture side or environmental side argues that the environment plays a significant role in a person’s mental ability. This discussion will look at the research and compare the evidence that supports both sides of the debate.

It has been a well known fact for some time now that traits such as hair, eye and skin colour, are all determined by specific genes passed down from our parents. The nature theory takes it further to say that traits such as intelligence, personality, aggression and sexual orientation are also in our genetics. This can be tested thanks to the birth of monozygotic or identical twins born from the same cell. Most data suggests that the genetic effect is more powerful. For example, identical twins reared apart show an average IQ correlation of about .75, which is even larger than DZ twins reared together (Burton, Weston, Kowalski, 2012). Although this correlation is not likely to be as strong in low socioeconomic groups as this is the group that has the greatest amount of risk factors. The greater amount of risk factors, the greater chance that a person will not reach their full potential (Hackman, Farah, Meaney, 2010).

Francis Galton was the first to use twin studies to collect evidence for this hypothesis to explain intelligence and many other researchers continuing to use this same technique. These studies involved sets of twins, both identical and fraternal twins, which are used to correlate IQ. They are conducted so that the results can compare the influence of heritability and the environment. As monozygotic twins share 100 percent of their genes, and dizygotic twins share 50 percent it gives us the ability to compare variables. If genetic factors are important in IQ, monozygotic twins should be more alike than dizygotic twins, siblings, and parents and their off-spring (Sternberg, Grigorenko, 1997). Biological relatives should also be more alike than adopted children and their adoptive parents or siblings. (Burton, Weston, Kowalski, 2012) These studies also involve comparing the results to the family, comparing IQ to parents and other siblings.

Research on adoption is also used for both sides of the debate, comparing variables between siblings or twins reared apart in order to examine the relative influence of genes and the environment. Adoption is highly beneficial for nature as it shows the effects of children brought up in the same family compared with those of different genetics in the family (Sternberg, Grigorenko, 1997). An example in favour of nature would be, if a set of monozygotic twins were to show similar intelligence even after being raised in different environments. It has been seen that monozygotic twins reared apart still have a higher correlation of IQ than dizygotic twins reared together(Burton, Weston, Kowalski, 2012). If genetics did not play a part in intelligence then dizygotic twins reared together would resemble each other strikingly close regardless of their only 50 percent in genetic relatedness. The interesting evidence is that dizygotic twins show a higher correlation than their other siblings even when reared apart supporting the theory once again that genetics does have a major influence on human intelligence. By using monozygotic twins as the control group any differences would have to be explained by environmental factors (Sternberg, Grigorenko, 1997). Studies have also shown that adopted children compared to the family’s biological children have no correlation although they have been brought up in the same family, school, and economic environment (Sternberg, Grigorenko, 1997). These studies have all found that it is the genetics that have a stronger influence on intelligence of a person rather than the environment.

On the other side of the debate we have the nurture theory that believes that intelligence is caused by a person’s environment. This means that environmental factors may include education, socioeconomic status, nutrition, parents behaviour, alcohol, criminal behaviour, emotional adaptation, down to the amount of time spent reading or even watching television amongst many others (Flynn, 1992). Research has focused much on infants and children, nutrition, twin and adoption just like supporters of the nature theory. It has also been noticed that IQ has been rising about 3 IQ points per decade across all industrialised countries, this means that since WWII the average IQ has risen over 1 standard deviation (Flynn, 1992). This suggests that social and environmental conditions lead to changes in IQ (Burton, Weston, Kowalski, 2012). Although studies have shown that nutrition plays a large role in development, the increase in IQ cannot be explained by diet alone. Another explanation is that children have experienced a wide variety of new technological creations stimulating them, helping with visual puzzles like those on IQ tests (Neisser, 1998). Many researchers have attempted to explain the theory, yet it is still unknown to what causes this increase in IQ. Many environmental factors have shown to have only slight contributions and are often unrelated to one another.

Psychological experiments of conditioning are an example of ways of controlling a person’s environment and show how important a person’s environment is in effecting how they think and therefore their intelligence. It has been demonstrated through experiments on children that fear can be learned. If it were not learned from the environment then it would likely never develop to show how important the environment is for the development of humans in many aspects. Burrhus Frederic Skinner’s experiments on pigeons is an example of how much is possible with conditioning (Burton, Weston, Kowalski, 2012). He was able to produce pigeons that could do figure eights, play tennis, dance and do certain actions in order to receive food. Although this is not an example of humans it shows a distinct connection between the environment and potential if just given the chance a person or animal is highly capable. This is an example of both nature and nurture working together, with the necessary genetics available and the environmental stimulus.

The study of twins for the nurture side is done by looking at identical twins and the fact that they are not 100% the same with different characteristics, behaviour and intellectual ability is proof enough that the environment must have had an impact on them. Just as adoption studies have also shown that a person’s environment plays a part in their assisting with intelligence (Sternberg, Grigorenko, 1997). Studies on interracial adoption in particular have shown that black children adopted by white middle class families who are tested before and later down the track have had a significant improvement of average IQ 83 to IQ 103, a 15 point increase and 20 point increase than their biological mother (Williams, 1997). This could be due to a numerous amount of factors whether it is schooling, opportunity, family or social environment. Schooling has been proven to improve a child’s IQ and with other environmental factors such as change of post code and resources combines can make significant changes to help with developing a person’s intelligence.

Looking at all the research covered although much has not been discussed, there is significant evidence that would prove that both sides have a great influence on our intelligence. There are high correlations for monozygotic twins even when raised apart are an extremely strong point in favour for nature. (Sternberg, Grigorenko, 1997). Although most studies are done on middle class white families where environmental risk factors are significantly lower than in lower class families. It does not show how influential the environment can be, if it were to be done on lower class monozygotic twins it would likely show a lower correlation and from their other siblings as well (Hackman, Farah, Meaney, 2010). Both sides work together complementing each other contributing and influencing a person’s intelligence. As this has been a topical debate for some time now, it isn’t surprising that an interactionist perspective has come about on explaining intelligence (Sternberg, Wagney, 1994). This perspective argues that both nature and nurture interact and work together, that neither nature nor nurture are capable of explaining intelligence entirely. ‘The person and the situation each contribute components to be integrated in successful performance’ (Sternberg, Vagner, 1994). A person is born with their genetic component and as they grow and experience life, the environment shapes and teaches that person assisting with intelligence. According to this theory it would be unlikely for a person to reach their full potential as the environment is filled with positive but also negative risk factors that would affect a person’s abilities. A person’s environment must require certain interactions and possibilities to learn in order to reach their biological potential already built in from birth.

Reference

Burton, L., Westen, D., Kowalski, R. (2012). Psychology (3^rd ed). John Wiley and sons inc.

Flynn, J. R. (1992). Cultural distance and the limitations of IQ. In J. Lynch, C. Modgil, & S. Modgil (Eds.), Education for cultural diversity: Convergence and divergence (pp. 343-360). London: Palmer Press.

Hackman, D. A., Farah, M. J., Meaney, M. J. (2010). Socioeconomic status and the brain: mechanistic insights from human and animal research. Macmillian Publishers Limited

Sternberg, R. J., Grigorenko, E. (1997). Intelligence, Hereditary, and Environment. Cambridge University Press

Sternberg, R. J., Wagney, R. K. (1994). Mind in context: Interactionist Perspectives on Human Intelligence. Cambridge University Press

Neisser, U. (1998). The rising curve: Long-term gains in IQ and related measures. Washington, DC, US: American Psychological Association.

Williams, W. M., Ceci, S. J. (1997). Are Americans Becoming More or Less Alike? Trends in Race, Class, and Ability Differences in Intelligence. American Psychological Association