Introduction
The phrase “nature versus nurture” was first used in its modern interpretation by the British psychologist, Francis Galton (Princeton, 2012). He began his studies concerning heredity in 1865, being moderately influenced by Charles Darwin’s publication “Origin of Species”, Galton was in favor of the idea that success was caused by superior inherited qualities, he hypothesized that human mental and personality traits were fundamentally inherited as they are in other animals (Indiana, 2012). The purpose of this paper is to establish which qualities relating to personality and development are proven to be at least partly inherited, and whether some other aspects of human personality and development are caused by environmental factors. The first section of the paper will be a brief overview of the research methodology of this field, the second section will contain a discussion of research relating to heritable factors and how they influence development, the third a look at how environmental interaction might influence personality and finally some criticism towards this field of study.

Main Body
The research of genetics and heredity is often difficult due to the vast amount of variables in the development of human beings, to keep variables to a minimum the most popular method of research in this field the study of twins. Twin studies involve comparing data produced by monozygotic (Identical) twins , these are twins who come from the same human ovum, to data from dizygotic (fraternal) twins who are born simultaneously despite not sharing a human ovum (GeneWatch, n.d) . Dizygotic twins share about 50% of their genes, where monozygotic twins share 100% (Winerman, 2004). When a particular trait is being investigated, data from Identical twins are compared to that of fraternal twins, if there is a higher correlation between the identical twins than the fraternal twins, then that particular trait might be influenced by genetics (Winerman, 2004). These tests can help determine how much of the variance in data can be attributed to genetic differences, the environment the twins live in and finally all other variables such as statistical error and unshared environment. (UNC, 2005)
Numerous twin studies have been done to determine what effect genetics have on personality traits. The word personality is used to describe a wide range of character traits, these traits have been classified in to smaller clusters in attempt to be more specific. The largest of these clusters are two “super-factors”, the first is extraversion which covers traits such as sociability, impulsiveness and liveliness, the other is neuroticism which includes characteristics such as moodiness, anxiousness and irritability (Plomin, 1996, p.91). A study review including more than 25000 pairs of twins demonstrated that there is an average correlation coefficient of 0.50 for both extraversion and neuroticism; the review also showed the predicted result of lower correlation between fraternal twins (Henderson, 1982 cited in Plomin, 1996, p.91). Similar results were again produced in two additional studies done in Sweden and Australia, the average extraversion correlation of these two studies was 0.515 (Identical) and 0.19 (Fraternal) and 0.50 (Identical) and 0.23 (Fraternal) for neuroticism (Plomin, 1996, p.91). Personality as a whole defined by neuroticism, openness, extraversion, agreeableness and conscientiousness has been found has a correlation of 0.43 in heritability (UNC, 2005). These studies clearly indicate that there is a large degree of heritability for major personality characteristics. Additional studies have been done to examine what effects genetics have on some other minor personality attributes. A study of identical twins that were raised in different environments produced high correlations in the following areas; sense of wellbeing, social potency, achievement, intimacy, stress reaction, alienation, aggression, caution, low risk taking respect for authority and imagination, with the typical correlation being 0.49, this correlation is as high as that of identical twins raised together (Plomin, 1996, p.95).

One of the most controversial parts of developmental psychology is the study of intelligence and heritability. Researchers have found that certain areas of the brain are highly heritable, including the regions that are primarily used for language and cognition, identical twins have a 95-100% correlation of brain structure in these areas, where fraternal twins have a lower but still discernable 60-70% correlation (Motluk, 2001). Other factors that correlate with IQ such as the amount of grey matter (processor cells) and white matter (processor connections) have been found to be largely genetically determined, also the quality of the white matter which is governed by a protective myelin sheath casing, has been proven to depend on greatly on genetics (Nature and Neuroscience, DOI: 10.1038/nn758 and Journal of Neuroscience, vol.26, p 10235 cited in Pearson, 2009). A study in which volunteers took a collection of tests that examined numerous individual abilities (verbal and spatial working memory, attention tasks, verbal knowledge, motor speed and visuospatial ability) found that subjects who did well in one of these areas also excelled in all the others, this ability is known as “g” (Motluk, 2001) even though “g” is not completely understood it is thought to have an organic underpinning in the brain, rather than just being a statistical variable (Plomin quoted in Motluk, 2001) The influence of genes on intelligence has also been found to increase with age, 41% of intellectual variation in children are attributed to genetics, this figure rise to 55% by adolescence and finally to 66% in young adulthood(Molecular Psychiatry, DOI: 10.1038/mp.2009.55 in Coghlan, 2009). A study involving 21000 people revealed the most convincing evidence yet, that a single gene can influence IQ, while there is a notable effect it is not significant enough to completely discount that intelligence depends on the effects of multiple genes, the gene called HMGA2 has the ability to alter IQ by 1.29 points (Coghlan, 2012). These studies indicate that intelligence is at least partly reliant on some biological factors, and these biological factors show some signs of heredity.

The other side of this debate is the nurture side, nurture is a term used to describe the environmental influences on a person. Research has been done to study how “nurture” affects aspects of behavior or personality. The above research on heritability shows that roughly half of personality variation in people tested is accounted for by genetics; the other half should therefore be somehow environmentally influenced. Tests conducted on siblings living in the same home showed very little correlation on their personality, the studies indicate that related people are only similar to the extent that their genetics make them similar (Harris, 1998, p.37). The results of these tests prove that the environment influences people to an extent that it accounts for half of personality variation but at the same time genes do not interact with environment in a predictable way, therefore we can conclude that social environment does influence personality but not in a way that two people exposed to the same environment will react to it the same way. Research suggests that many factors of developmental psychology that were previously thought to be influential, such as family structure, parenting style, stay-at-home versus working mother, sexual preferences of parents, conception method of child (natural versus in vitro), marital status of parents and amount of siblings all appear to have either no effect or no predictable effect on personality and behavior (Harris, 1998, p.49-52).
There have been many contributing viewpoints to the “Nature versus Nurture Debate” but some hold the opinion that it is a nonsensical debate, that ”Nature” and “Nurture” are dependent on so many of the same factors that they are inseparable in principle. Judith Harris argues that It is impossible to identify what exact influence genes and parenting styles have on the development of a child, as the parenting style of adults are to some extent just a function of the parents own genes (Harris, 1998, p.21) A gene that is not acted upon or an environment without genes amounts to nothing, it is logical to assume that these functions are inseparable and the entire issue of learned versus innate assumes a pre-existing reciprocal relationship that does not exist in reality (Candland, 1993, p.69).Hans Kummer offers an analogy to illustrate the absurdity of the “Nature versus Nurture Debate”, to ask what effect genes or environment has on individuals is similar to asking what produces a drumming sound the drummer or the drum?(Hans Kummer quoted in Keller, 2010)

Conclusion
It is clear from the research that there are many aspects of the human personality that is influenced by the genetic makeup of the individual, and that whatever is not accounted for by genes must logically be caused by environment, but the research does not indicate any pattern of causal links between behavior-personality and any particular environmental influences. The inseparableness of nature from nurture in practice makes research into this field particularly difficult. The debate itself is also difficult to justify. It seems to be akin to asking if deaths by nut allergies are caused by the environmental act of eating the nut or the individual’s genetic reaction to the nut itself, or what percentage responsibility should be attributed to which factor.

References
Candland, D. (1993) Feral Children and Clever Animals. New York: Oxford University press
Coghlan, A. (2009) Intelligence: Nature outpaces nurture as kids get older. New Scientist, 15 July , pp. 10
Coghlan, A. (2012) Best evidence yet that a single gene can affect IQ. New Scientist, 18 April , pp. 14
GeneWatch (n.d) Twin Studies. GeneWatch. Retrieved 18 April 2013 from http://www.genewatch.org/sub-564682
Harris, J. (1999) The Nurture Assumption: Why children turn out the way they do. London: Bloomsbury Publishing
Indiana University (2012) Francis Galton. Indiana University. Retrieved 18 April 2013 from http://www.indiana.edu/~intell/galton.shtml
Keller, E. (2010) Goodbye, nature vs nurture. New Scientist, 20 September, pp. 28-29
Motluk, A. (2001) IQ is inherited, suggests twin study. New Scientist, 05 November
Pearson, A. (2009) High-Speed brains are in the genes. New Scientist, 11 March, pp.12
Plomin, R. (1996) Nature and Nurture: An Introduction to Human Behavioral Genetics. Pacific Grove: Brooks/Cole Publishing
Princeton University (n.d) Nature versus Nurture. Princeton University. Retrieved 18 April 2013 from http://www.princeton.edu/~achaney/tmve/wiki100k/docs /Nature_versus_nurture.html
UNC (2005) Twin Studies: what can they tell us about nature and nurture? University of North Carolina. Retrieved 18 April 2013 from http://www.unc.edu /~gguo /papers /05%20twin%20studies%20Contexts.pdf
Winerman, L. (2004) A second look at twin studies. American Psychological Association, vol 35(4), pp.46