Twin and Adoption Issue and the Nature-Nurture Debate - Essay Example

The results of twin and adoption studies have now resolved the ‘nature-nurture debate’. Critically discuss the extent to which you agree with this statement and why." Introduction The question of whether individual differences should be attributed to their genes or environment remains a central issue to how policy makers, practitioners in various fields and the public in general perceives and reacts to issues such as child development, health, education, psychological and physical disorders, drug abuse and criminal behaviour among many other issues (Keating, 2010). Over the years, there have been long-standing debates on the relative importance of hereditary (genetic) factors versus environmental factors in influencing individual dispositions and behaviour. These debates have been dubbed the “nature-nurture” debate. The phrase “nature and nature” can be traced back to discussions in the Victorian era by Francis Galton who explored the influence of genetics and the environment in social development. Since then nature-nurture discussions has sparked the interest of many scholars and has been subject to significant debate and controversy (Keating, 2010; Moore, 2003). The continuous debate on nature versus nurture have compelled scholars to carryout a wide range of empirical studies in a bid to determine whether hereditary or environmental factors have a stronger influence on individual behaviour and dispositions. Twin and adoption studies have been vastly used as a tool for dissecting the nature versus nurture debate. Twin studies often involve comparisons between identical or monozygotic twins reared together or separated at birth and reared in different environments. On the other hand, adoption studies involve comparisons between children, their adoptive parents, siblings and in some cases comparisons are conducted with their biological parents (Agrawal & Lynskey, 2008; Wright 1997). Although a considerable number of twin and adoption studies have been conducted over the years, there is still no consensus whether hereditary or environmental factors have a strong influence on individual dispositions and behaviour (Torgersen et al 2000; Silventoinen et al, 2010). Some studies have established that hereditary factors have a stronger influence whereas others have found that environmental factors play a central and critical role in how individuals eventually turn out (Agrawal & Lynskey, 2008; Levitt 2011). Additionally, the findings of a number of twin and adoption studies have employed contentious methodological approaches that put to question the validity of their findings (Beirut et al, 1998; Cadoret et al, 1996; Seglem, Waaktar, Ask & Torgersen 2015). As a result, it is plausible to argue that, due to the conflicting results of many twin and adoption studies and the questionability of some of the methodological approaches used in these studies, the findings obtained from these studies do not provide compelling evidence that can resolve the ‘nature-nurture debate’. This paper seeks to critically examine the extent to which the results of twin and adoption studies have resolved the ‘nature-nurture debate’. It will argue that the results of twin and adoption studies are yet to resolve the ‘nature-nurture debate’ since they are conflicting and are marred by methodological errors. This paper will examine both the nature and nurture paradigms and critically assess the validity of studies that support these arguments. Nature-Nurture Paradigms and Supporting Twin and Adoption Studies The nature paradigm is based on the notion that individual disposition, abilities and behaviour are centrally influenced by their genetics or hereditary traits. Over the years, a number of twin and adoption studies have provided support for the nature paradigm (Agrawal & Lynskey, 2008). Some of the notable adoption studies were conducted by Cadoret et al (1996) and Beirut et al (1998) who compared the rate of alcohol problems among children of biological parents with alcohol dependency and adopted children who had no contact with their alcohol dependent parents. The findings of these studies supported the notion that genetic traits have a strong influence on individual disposition and behaviour particularly towards alcohol consumption. However, Agrawal & Lynskey, (2008) suggest that the findings of these studies are not conclusive due to the limitations of the methodology employed. The samples of biological and adoptive parents selected in these studies are not representative of the population. This is mainly because biological parents are likely to have higher rates of drug dependence that adoptive parents who are relatively older and socially advantaged (Agrawal & Lynskey, 2008). Moreover, another inadequacy of these twin and adoption studies is that they use small samples. In this regard, Burt (2009) argues that the use of small sample sizes is a major limitation for twin and adoption studies examining genetic influence versus environmental influences. The small samples used in many studies are not representative of the population. Thus the results of these studies are not conclusive and therefore cannot be used as a basis for resolving the nature-nurture debate. Additionally, some twin and adoption studies can be considered to be inconclusive since they produce conflicting findings. In this regard, Mishra (2008) observes that some studies have produced conflicting results on the nature-nurture debate. When in comes to the issues of whether children’s intelligence quotient (IQ) is influenced by genetics or the environment, in some cases twin and adoption studies have found that there were stronger IQ similarities between adopted children and their biological parents than their adoptive parents. In other cases, the study found that the IQ of the adopted children were more similar to their adoptive parents than their biological parents (Mishra 2008). These conflicting findings are not helpful in resolving the nature-nurture debate. Conversely, the nurture paradigm assumes that individual dispositions and behaviour exclusively emanate from environmental influences. It further assumes that at birth the human mind is a blank slate that is slowly filled and shaped by experiences. Sigmund Freud is among the notable proponents of the nurture assumption. In his psychoanalysis theory, Freud (1900) argues that an individual’s psychological state and behaviour are largely shaped by their experiences in their formative years and interactions with the parents or caregivers. He further argues that two parents of the opposite sex bring about significant changes in the dynamics of children’s growth and development. In the course of their formative years, Freud observes children are likely to identify more with the parent of the same sex by adapting, imitating or forming similar characteristics as their same-sex parent (Freud 1900). Thus according to Freud, individuals influenced by their experiences and interactions in their environments as opposed to their hereditary traits (Harris, 2011). Freud’s theory has been criticised for lacking empirical support and being too simplistic to explain the complex nature of the human mind (Westerink 2009). According to Levitt (2013) and Craddock (2011), investigating the influence of nature and nurture as explanation of human behaviour through twin and adoption studies is impractical and unproductive. This is mainly because, this approach over simplifies issues and does not take into account the complexity involved in gene-environment interaction. Many twin and adoption studies carried out to resolve the nature-nurture debate over-simplify things by trying to single-out one factor as the most dominant influence yet both nature and nurture interact to influence behaviour in complex and not yet fully understood ways (Levitt 2013). Recently, a multi-informant twin study conducted by Seglem, Waaktar, Ask & Torgersen (2015), examined the variance in smoking involvement among monozygotic and dizygotic adolescent twin pairs of both sexes reared together. The study explored the extent in which smoking involvement of twin pairs is attributed to genetic or environmental effects. Following the collection and analysis of data collected through questionnaire administered to the subjects close families, it was established that adolescents lifetime smoking involvement was moderately influenced by hereditary traits (37 %) and mainly by the environment (56 %). Although the results of this study support the notion that nurture is a stronger influence on individual dispositions and behaviour, its results can be put to question due to the limitations of the methodology employed. Based on the methodology used, there is the possibility of assortative or non-random mating, which often occurs when individuals with a similar trait mate with one another more frequently than expected with a random mating pattern. Some genetic studies suggest that assortative mating in regard to of substances such as alcohol and tobacco offers bias estimates of the genetic and environmental parameters (Agrawal et al. 2006; Ask et al. 2012). Another methodological error evident in this study revolves around the bias involved in selecting the participating families on the basis of socio-economic factors. In the past, genetically informative studies have established genetic effects tend to be stronger in more advantaged socio-economic background especially when in comes to antisocial or psychopathic behaviour (South & Krueger, 2011; Tuvblad et al, 2006). Thus the selection of participating families based socio-economic background was biased and not representative of the target population. The methodological errors evident in this study put to questions the validity of its results in resolving the nature-nurture debate. Conclusion A critical look at the findings of this paper, it is evident that there is no consensus among various twin and adoption studies regarding whether hereditary or environmental factors have a strong influence on individual dispositions and behaviour. Some studies have found that hereditary factors have a stronger influence whereas others have established that environmental factors have a more strong influence. Moreover, the methodologies employed in some of these studies raises questions on the validity of the results generated. In most cases, the sampling methods used in many twin and adoption studies are not representative of the population. Based on these issues, it is plausible to argue that due to the conflicting results of many twin and adoption studies and the questionability of some of the methodological approaches used in these studies, the findings obtained from these studies do not provide compelling evidence that can resolve the ‘nature-nurture debate’. As a result, there is need for future research studies to take into account the complexity involved in gene-environment interaction rather than simplifying and single-handedly focusing on verifying the influence of one factor over the other. There is also need for more suitable methodologies to be used particularly in the process of selecting a representative sample. References Agrawal,A, Heath, A.C., Grant, J.D., Pergadia, M.L., Statham, D.J., Bucholz, K.K, Martin, N.G. &Madden, P.A.F (2006). ‘Assortative mating for cigarette smoking and for alcohol consumption in female Australian twins and their spouses’. Behaviour Genetics 36(4): 553–566. 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