The nature—nurture debate
Issues and debates
The nature—nurture debate focuses on the degree to which behaviour is inherited or learned. The nature part of the debate sees behaviour as being determined by the genes an individual inherits, with no input at all from environmental factors. The nurture part of the debate, however, sees all behaviour as determined solely through learning via environmental influences, with no hereditary genetic influences. Research does not indicate that behaviour is genetically determined, so nature, by itself, cannot explain the causation of behaviour. However, research does show that many behaviours have a genetic component, so the debate mainly focuses on the relative importance of heredity and environment in determining behaviour. Research has focused on twin studies, where the nature point of view is favoured if MZ twins (genetically identical) are more similar in behaviour than DZ twins (50 per cent genetically similar), and adoption studies, where nature is favoured if adopted children’s behaviour is more similar to their biological parents, as well as gene mapping studies, which try to identify specific genes associated with specific behaviours. The interactionist approach sees individuals as having genetic potentials for different behaviours, with environmental factors determining how much of the genetic potential is realised for each behaviour.
Fig 8.3 Does our behaviour stem from our genetics or our upbringing?
Grootheest et al. (2005) conducted a twin study to assess the degree to which OCD is an inherited condition under genetic control. The researchers conducted a meta-analysis of two types of twin studies: first, ones conducted between 1929 and 1965 using outdated diagnostic criteria (9 studies comprising 37 twin pairs) and, second, ones conducted since 1965 using modern diagnostic criteria (19 studies comprising 9,997 twin pairs). It was found that in children, OCD had a heritability influence (the degree to which the condition was genetic in nature) of 45—65 per cent, while in adults OCD was found to have a heritability influence of 27—47 per cent. It was concluded that, especially in children, there is a genetic component to OCD. However, as OCD was not found to be totally genetic in origin, it supports the interactionist approach that OCD occurs through a mixture of genetic and environmental influences.
• Plomin et al. (2013) used gene-mapping techniques with a sample of 3,154 pairs of 12-year-old twins to find that genetics accounted for about 66 per cent of the heritability of the cognitive features of depression, such as negative schemas, which suggests that depression is largely a result of nature.
• Turnbull (1961) reported on Kenge, a pygmy who had lived all his life in dense rainforest. When taken to wide open savannah grasslands he perceived buffalo miles away as ants, but a short distance away. It seemed that learning experiences (from living in dense rainforest) had shaped his perceptual abilities, supporting the nurture viewpoint.
• Skodak & Skeels (1949) found the correlation between IQ (intelligence) scores of adopted children and their biological mothers rose from 28 per cent at age 4 to 44 per cent at age 13, supporting the nature viewpoint. However, Scarr & Weinberg (1983) found adopted children’s IQ levels moved away from those of their biological parents towards those of their adoptive parents, supporting the nurture viewpoint.
The nature—nurture debate in recent times has moved from the argument between the extreme viewpoints of nature and nurture to the general acknowledgement that an interactionist stance is seen to be appropriate. The argument now is based on the relative influence of nature and nurture.
Research on the relative heritability of a characteristic varies greatly. This could be due to many things such as sample size, methodology and age. It may indeed possibly be due to the fact that some people are more susceptible to environmental influence than others. For example, with intelligence, the higher an individual’s genetic potential for intelligence (nature), the more environmental learning experiences (nurture) play a part in determining that individual’s actual level of intelligence.
Assessing the relative influence of nature and nurture is fraught with difficulties. Even using twin studies is problematic due to the assumption that the only difference between MZ and DZ twins is their genetic similarity. Parenting styles differ in that MZ twins are treated more similarly than DZ twins. This means the difference in concordance rates could be due to nurture rather than nature.
Because intelligence has been shown to be considerably affected by environmental factors (nurture), it has allowed researchers to identify the types of interactions that can be made to help boost children’s IQ, such as diet, exercise and social stimulation, as well as teaching.