Darwin’s idea of evolution of species through natural selection revolves around the notion that individual differences are heritable, thereby leading to heritable changes from generation to generation, and the emergence of a completely new species. Darwinism completely shifted the view of human behaviour, thereby giving rise to two broad approaches to the study of animal behaviour in Europe and America (Harman, 2007). Two pioneers of the European school, the Austrian Konrad Lorenz and the Dutch zoologist Niko Tinbergen, collaborated in the founding of “ethology”, the scientific study of behaviour, in the 1930s. J.B. Watson, who was heavily influenced by Pavlov’s classical conditioning, pioneered the American school, and established the foundations for the experimental approach to behaviour in 1924 (Moore, 2011). One of the oldest and most controversial arguments in the history of psychology is undoubtedly the nature versus nurture debate, which concerned with the extent to which certain aspects of behaviour are inherited or learned characteristics (Cullen, 2005). This paper will explore the core of the nature versus nurture debate and the manner in which psychologists have attempted to resolve this issue over the years, through a number of experiments and scientific investigations.
Nature refers to the attributes of behaviour that are acquired through genes or are inherited while nurture refers to all behavioural attributes that are acquired through experience, as a result of environmental influences after conception. The nature versus nurture debate has been hotly contested throughout history, giving rise to two variant schools of thought namely the nativists and the environmentalist/empiricists (McLeod, 2007). The nativists believe that behavioural attributes are purely hereditary, that is, they are as a result of evolution; in that respect, the nativists regard individual differences to be the result of each person’s unique genetic coding. The nativists have a strong view that all the human characteristics that are present at birth and those that emerge earlier on in development are directly linked to genetic factors while those that emerge later are simply as a result of maturation (Eagly & Wood, 2013). The implication of the nativist argument is that the human species has an inner biological clock that flips behaviour characteristics on/off in a pre-programmed manner as is evinced by the bodily changes that affect individuals’ physical development in the early adolescence stage. Nativists further extend their maturation argument to explain the emergence of attachment in infancy, as well as the development of language and of the mind as individuals mature into adulthood.
Nativists explain that the unique coding of genes in every cell accounts for the individual traits that are inherent in different people; for instance, physical characteristics such as hair colour, eye colour and height, among others have been attributed to genes. However, it is not yet clear whether some of the more abstract individual characteristics such as personality, sexual orientation and intelligence are determined by genetic factors (Williams, Myerson & Hale, 2008). One of the hotly contested issues in the nature theory has been the supposition that the gays are born gay, and that their sexual orientation is accounted for by the presence of a “gay-gene”, which is coded in their DNA (Johnson, 2003). The nature theory has also spurred significant controversy for suggesting that criminal acts, the likelihood to divorce and aggressive behaviour can be explained by the presence of behavioural genes encoded in individual’s DNA (Malone, Taylor, Marmorstein, Mcgue & et al., 2004).
On the other extreme end of the spectrum are the environmentalists/empiricists who insist that behavioural attributes are acquired experientially as individuals interact with factors or forces of the environment. The implication of the empiricists’’ argument is that the human mind is a blank slate birth; however, through interaction with forces/factors of the environment, this tabula rasa is gradually filled up with behavioural characteristics (Eagly & Wood, 2013). In that respect, the environmentalists strongly believe that all psychological features and changes in behaviour are learnt gradually through infancy and childhood; furthermore, environmentalists argue that maturation only affects biological qualities and not the critical psychological facets of child development. To support their conjecture, the environmentalists have insisted that all the aspects of child development that are psychologically important are as a result of how the child is brought up. For instance, environmentalists argue that an infant establishes an attachment as a response to the love and care it is receiving and not because it is biologically tuned to do so. Moreover, when it comes to the issue of language acquisition, environmentalists believe that children acquire language by imitating the speech of significant others in the environment. Concerning cognitive development, environmentalists argue that children’s progress is highly dependent on the level of stimulation in their environment, as well as the civilization within which the child is raised (Riedel, Heiby, & Kopetskie, 2001). The environmentalists insist that though the genetic influence on abstract traits such as individual’s personality may exist, the environment is the ultimate origin of human behaviour; thus, the nurture theory suggests that human beings can be conditioned to induce new forms of behaviour or to alter existing behaviour. Proponents of the nurture theory such as John Watson were strongly convinced that they could train babies to become any type of specialist regardless of their potentialities, talents or race.
To resolve the nature versus nurture question, psychologists have performed adoption and twin studies; twin studies, particularly of fraternal twins, have been at the core of the nature versus nurture debate. Identical twins have been thought to be the most likely indicator of the impact of biology on human traits and psychopathology because their genotypes are duplicates of each other (Horwitz, Videon, Schmitz & Davis, 2003). On the other hand, fraternal twins have proved to be invaluable as a basis for comparing with the identical twins, particularly because they share exactly half of their genes with each other. It has been established that even though identical twins’ genotypes are perfect duplicates of each other, they may go through varying life experiences that shape their personality, behaviour and psychopathology in unique ways that make them different (NPR, 2012). Adoption studies have also been used to in an attempt to disentangle the nature versus nurture argument; adoption studies have been potent in explaining the heredity and environmental impact on human attributes and psychopathology. Adoption studies include biological parents and environmental parents as two of the factors that may potentially explain the variations in individuals’ behaviour and personality. The behavioural attributes between children and their biological parents have been attributed to genetic factors while behavioural links between children and their adoptive parents have been linked to the environment (Plomin, 2011). For instance, children of schizophrenic mothers have been found to be highly at risk of being schizophrenic themselves even if parents that are not schizophrenic adopt them. This implies that the environment in which children are raised in does not necessarily rule out the influence of genetic factors in a child’s development (Knowlton, 2005). Apart from the adoption and twin studies, family studies have also been carried out, in an attempt to disentangle the nature versus nurture argument; family studies have mostly been used to identify the degree to which mental illness is inheritable in families. Family studies are undertaken, mostly through molecular genetic studies, the most common of them being linkage analysis, which attempts to identify a particular gene on a chromosome in the human body. However, not even the family studies have been conclusive enough, to rest the nature versus nurture debate; just as the twins and adoption studies, family studies are inadequate in resolving the dilemma in the ongoing debate.
In contemporary times, the nature versus nurture debate has gradually lost its initial fire as both sides of the argument have increasingly raised valid points that are worth of consideration, thereby leading to a shift in the debate (Traynor & Singleton, 2010). Psychologists have come to appreciate the facts from both sides of the divide, which could potentially be truthful, thereby dropping their extreme positions in the famous nature versus nurture debate in favour of an integrated viewpoint. In other words, psychologists are gradually expressing the view that both the environment and genetic factors have a potential influence on the development of behavioural characteristics in human beings and that neither the genes nor the environment can account for all behavioural changes in isolation (Keller, 2010). Consequently, psychologists have reformulated the nature versus nurture question in terms of “how much” behaviour is inherited and “how much” is as a result of learning in the environment. This new psychological approach is aimed at establishing whether it is the genetic or environmental factors that have the most significant influence on child development rather than merely asking whether it is one or the other. The view that both the environmental and genetic factors have a significant impact on the development of children has pervaded the history of Psychology from the 19th century onwards (De Waal, 1999) thereby instigating scientific enquiries that sought to determine whether genes or environment had the greatest influence on child development.
Overall, despite the concerted efforts by psychologists to explain the origin of behavioural attributes over the years, it is not yet clear how much of behaviour is attributable to genetics and how much is because of learning in the environment. Evidently, the existence of behavioural genes that are responsible for behavioural change in individuals has been proven through twins and adoption studies; experimentation with fraternal twins has indicated that they are capable of developing similar behavioural traits as if they have been raised together, even if they are reared apart. Nevertheless, it has also been established that the environment has a significant impact on the manner in which identical twins behave since even though their genotypes are perfect duplicates of each other, they may go through varying life experiences that shape their behaviour differently. This has further fuelled the long and pressing question of whether individuals’ behavioural attributes are inborn or whether they are learnt through interactions in the environment, thus, the nature versus nurture debate still goes on.
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