According to Begley S. (2003), intelligence was defined as “general cognitive ability seems to reflect memory skills, verbal and spatial abilities, and abstract reasoning.” There are two factors that influence the inheritability of the intelligence. There had been a long argument with regards to the importance of heredity and environment as factors that determine the development of intelligence (Wenrick J.,1940). To find out the heritability of intelligence (IQ), most common method uses to determine is IQ testing which according to Sundet J. et al. (1988) heritability is higher in children (Mitchell F., 2013). There are many evidence to support that both heredity and environment play a part in the development of intelligence. However, in this essay, the impact of both and genes and environment on the inheritance of intelligence in children will be discussed as well as the relationship of this factors.
Some report argued that genetic is the main influence of the inheritance of IQ. A review study of Cohen D. et al. (1999) suggested that despite the small impact on the correlation for genetic on intelligence is 0.1 which considered low, when this correlation is compared to the correlation of the shared environment which is zero, the genes is shown to have greater impact on the heredity of IQ. Moreover, the data from Plomin R. and Spinath F. (2004)’s article also support the genetic influence of the IQ inheriting. Plomin R. and Spinath F. compared the average correlation of the monozygotic twins (MZ) and the dizygotic twins (DZ), include all conditions; reared together and adopted-apart. The MZ twin average correlation is 0.86 while the DZ twins are 0.6. This emphasises the genetic influence on the inheritance of intelligence. Although Cohen D. result did not show a large difference in the dependency of intelligence on genetic but Plomin R. and Spinath F. twins’ correlation help backed that intelligence inheritance relies on genetic. Therefore, showing that genes play a part in the inheriting of IQ.
On the other hand, the environment is shown as a great influence on children’s who were raised by the same family IQ (Mitchell P. & Ziegler F., 2013). This can be supported by Visser C. (2009), that the development of intelligence can increase to approximately 70% depending on the different type of environment. In addition, the statistic from Plomin R. and Spinath F. (2004) also supported the statement. The research shows the correlation for adopted children and the adoptive parent is 0.19 while the adoptive siblings are 0.32. According to Plomin R. and Spinath F. the correlation act as an evidence showing the significance of the environment because the only similarity that the adoptive siblings shared in common is their environment. Nisbett R.’s study illustrates the dependency of intelligence on the environment, for instance when a child was raised in a good environment his or her intelligence would likely to increased. With the used of correlation in the Plomin R. and Spinath F.’s article, its shows the contribution of shared environment, which in this case can be referred to being raised in the same family, to the development of intelligence. Thus, showing that with quality and similar environment, inheritance of intelligence.
According to Lynn R. et al. (1989) both genes and environment have an impact on the inheritance of intelligence, this is supported by the result they achieved from their research. the result shows the correlation for IQ of 386 pairs of siblings extracted from the 2093 children participating, which were 0.48. the correlation backed up Lynn R. et al.’s statement as when they compared the total IQ score they obtained from their research to research done by other researchers (in this case the twins study by Eysenck, 1979), the correlation was shown to be close. thus, proving the relationship of genetic and IQ because the Dizygotic twins (raised by the same family) shared the half of the similar genes which is the similar case for the siblings who shared some similar gene. Likewise, with the similar characteristic and IQ correlation score, it shows that genetic inheritance on intelligence. Furthermore, the difference between the final IQ’s correlation for the siblings and the predicted siblings’ correlation is 0.134 provided the measurement of the effect of shared family environment on intelligence. Hence, with the heritability provided for the data and the discussion mentioned in Lynn R. et al. illustrate that both heredity and environment are the influencers of inheritance of intelligence.
Furthermore, an article from Penrose L. (1933) also found that there is association between both genetic and environment with intelligence. The finding from Bartels M. et al. (2002) supported that both genes and environment are influencing the intelligence of the children. Depending on the period of time, the dependent of intelligence on heredity and common environment might vary. For example, during the 40’s the heritability of male participants was raised to 0.76 showing the genetic dependency. In contrast, during the 60’s the impact of genes was lower while the environment was part of 50% of the variance (Sundet J. et al., 1988).
Elaboration: Therefore, showing the relationship between the environment and heredity as although they both have an influence on the inheritance of intelligence but one might increase while the other is decrease like shown in the Sundet J. et al’s article. Hence showing another link between the impact on environment and genes on intelligence.
In conclusion, as mentioned before despite having argue for a long time about which factor is more important to the inheritance of intelligent, it is agreeable that both environment and genes have their own part to play in influencing the inheritance of intelligence. Some studies might investigate the role of environment and hereditary separately, however, studies like Lynn R. et al. showed that the role of both genetic and environment co-exist with each other. The Cohen D. et al. article also mentioned the close relation between the impact of environment and the impact of genes on the intelligence inheritance, although claim that this shows the greater influence from genetic. And study like the sundet J et al. also brought up about the third factor that affects the influence of both environment and heredity, which can be important and needed to be researched on further. Moreover, most of the research are likely to indicate environmental factor as being reared by the same family environment. However, the environment can be more than just growing up in the same family, thus further investigation is needed in the future to allow deeper exploration of the effect of environment on the development of intelligence