Nature versus Nurture

Introduction

Since the first attempt to study nature and nurture in the development of personality and behavioral traits over a century ago, the question that has divided developmental psychologist is whether nature or nurture has the greater bearing (Plomin, 2002). What behavior geneticists try to do is to figure out what is responsible for the differences; that is, to what extent do people differ because of differences in genes, environment, or a combination of both (Haig, 2003). In attempting to understand the intricacies of this issue it is useful to go back to its roots. The idea that people differ in their personality and temperament goes back at least to the time of Galen in the second Century (Rutter, 2006). Galen proposed temperamental traits into sub-divisions of four different qualities - melancholic, sanguine, phlegmatic and choleric (Rutter, 2006). Galen believed that these inborn humors not only determined a person's behavioral and emotional tendencies but he used them also to refer to their bodily dispositions and susceptibility to certain diseases. While Galen's theory did not survive him the concept of psychological states being biologically based was prominent until the emergence of Freud's Psychoanalytical theory and Pavlov's Behaviorism theory (Rutter, 2006). With these two renowned figures came a surge of support in the overwhelming importance of a person's environment throughout their development (Rutter, 2006). However, while there are those who are adamant that it's either nature or nurture, in the past fifty years there has been acceptance from many on either side that both nature and nurture play an important role in personality and behavioral development (Plomin, 2002).

Behavioral Understandings

Behavioral geneticists use family, twin and adoption studies as a basis for their argument (Lerner, Bearer & Garcia Coll, 2004). A significant contributor to studies in behavioral genetics, provides this definition: Behavioral genetics is the genetic study of behavior, which includes quantative genetics (twin and adoption studies) as well as molecular genetics (DNA studies) of human and animal behavior broadly defined to include responses of the organism from responses measured in the brain such as functional neuro-imaging to self-report questionnaires” (Lerner, Bearer & Garcia Coll, 2004, p. 2). One of the first twin studies was conducted by Bouchard in 1979 when he found a set of monozygotic twins, babies from an egg that splits into two, separated at a few weeks old who had many physiological and psychological similarities (Ridley, 2003). Since Bouchard's initial study it has been proven that, while monozygotic twins raised together have many similarities, those separated an early age have an even greater likeness (Ridley, 2003). Since twins being raised together are more likely to highlight their differences in order to maintain some element of independence, behavioral geneticists argue that this indicates a strong genetic underpinning in human development (Ridley, 2003; Rathus, 2004).

Research conducted by Grilo and Pogue-Geile (1991) correlated the familial relationships for extroversion. The study included monozygotic twins reared together and apart, dizygote twins reared together and apart, biological parents and children, biological siblings, adoptive parents and children ...