Longstanding Questions & Controversies About Human DevelopmentEdit
What exactly causes development and what course does it follow? Developmental theorists have pondered and debated over these questions for decades. In an effort to explain the complexities of human development, psychologists (such as those discussed above) have proposed and tested theories over the years; however, consensus around development’s true cause and course has yet to be established (Shaffer, 1999).
Throughout psychological history and still in present day, three key issues remain among which developmental theorists often disagree. Particularly, often disputed is the role of early experiences on later development in opposition to current behaviour reflecting present experiences – namely the passive verses active issue. Likewise, whether or not development is best viewed as occurring in stages or rather as a gradual and cumulative process of change has traditionally been up for debate – a question of continuity versus discontinuity. Further, the role of heredity and the environment in shaping human development is a much contested topic of discussion – also referred to as nature/nurture debate.
The Active/Passive Issue:
A key topic of debate among developmental theorists revolves around the issue of ‘active’ or ‘passive’ development (Shaffer, 1999). Of interest is whether or not children should be viewed as active contributors to their own development (i.e. influence how others treat them) or as passive recipients impressed upon by others and their environment.
Only a generation ago, most people, including psychologists, believed that the “footprints of our genes and early experience [were] set in cement” (Myers, 1998, p. 143). They believed that in response to these events, one’s development would follow a stable life course. For example, early psychoanalytic theorists like Freud believed that children were passive beings moulded by their parents.
On the other hand, psychologists like Erikson believed that children develop as a response to their adaptations to their environments and social/cultural influences. It wasn’t until the 1960s, that new findings surfaced suggesting that personality and development evolved with time and frequently undergo surprising and unpredictable changes. For example, longitudinal research by Jean Macfarlane (1964), in which 166 people were followed from infancy to age 30, found that many of the participants who had severely troubled childhoods and adolescences were later rated as some of the most “mature and competent” adults within the study. Research by Thomas and Chess (1986) report similar results.
Thus, as Bernice Neugarten (1980) once said upon reflecting on her work on changes within the life cycle, “the primary consistency we have found is lack of consistency”.
The Continuity/Discontinuity Issue:
The debate among theorists about developmental change occurring steadily and over time or suddenly and perhaps in stages has been longstanding and has fuelled much of developmental thinking and research.
Continuity theorists view human development as an “additive process that occurs gradually and continuously, without sudden change” (Shaffer, 1999, p. 40). Whereas discontinuity theorists describe developmental growth as occurring through a series of abrupt changes, each which “elevates the child to a new and presumably more advanced level functioning” (p. 40).
In our account of prominent historical developmental researchers, several stage or discontinuity theorists have been considered: Piaget on cognitive development, Kohlberg on moral development, Erikson on social development and Freud on personality development. Over time, research has been conducted to support the idea that stage development may be true to certain times within development. For example, Thatcher, Walker and Guidice (1987) has found that there are spurts of brain growth during childhood and puberty that approximately correspond to Piaget’s proposed stages. However, despite the groundbreaking work of these theorists, they have also faced criticisms demonstrating that life may not always progress through a fixed, predictable set of steps as suggested (see criticisms of each theorist above). Rather, theorists such as Vygotsky, discuss change as it occurs progressively and in accordance with ever-changing social and cultural influences.
The Nature Nurture DebateEdit
One of the most important and long standing questions that has been debated by both philosophers and psychologists is whether or not we develop as individuals because of the biological contributions we receive from our parents (genetics) or environmental experience we gain after birth (Myers, 1998).
Here is how a few of the most prominent philosophers and psychologists weighed in on the issue:
- In the 17th century, John Locke used the term "tabula rasa" to describe the state of the mind at birth as a "blank slate." Locke posited that it is only through our senses (experiences) that we come to develop ways of perceiving and ultimately understanding the world (Myers, 1998). This view of empiricists is in contrast to that of nativists, who believed that certain elementary truths are innate to the human mind and need not be gained through experience.
- G. Stanley Hall was one of the earliest psychologists to propose a theory of adolescent development. He believed that all individuals pass through the same four stages of development and that progression through these stages was based on physiological factors (genetics). Development was framed as an "unchangeable, universal pattern, and the effects of the environment [were thought to be] minimal" (Dacey & Travers, 1996, 284).
- Sir Francis Galton assumed that "talent is transmitted by inheritance in a very remarkable degree" (Galton, 1865, 157). As support for this claim Galton argued that the most desirable human traits, such as height or intelligence, tend to run in families. Taking this notion one step further, Galton believed that we as a society could strive for human betterment by mating those people with the most desirable traits, as they would pass on their genes and likely produce the most favourable offspring. It was this belief that founded the Eugenics movement.
Today, it is generally agreed upon that it is neither genetics nor environment alone that determine how we develop as individuals; but rather, genetics, environment, and the interaction between the two, are all thought to have a part in explaining how we develop. Traditional studies within the field of child development have primarily focussed on the impact that the family has on children. However, these studies confound the influence of genetics and environment because parents are the providers of both genes and environment. In order to tease apart the influence of genetics and environment, designs that are genetically sensitive must be utilized (Jenkins, 2006).
Twin Studies are one way to help tease apart genetic and environmental influences. Using this design, researchers compare monozygotic twins (MZ twins), who share 100% of their genes, to dyzygotic twins (DZ twins), who only share 50% of their genes. Knowing how genetically similar twins are and comparing how behaviourally similar they are allows researchers to infer the relative importance of genes and environment. If monozygotic twins (MZ) are proven to be more similar on a given trait or characteristic when compared to dyzygotic twins (DZ), it would suggest that there is a strong genetic component to that trait or characteristic. However, if monozygotic twins (MZ) are found to be no more similar to each other on a given trait or characteristic when compared to (DZ) twins, it would suggest that there is a strong environmental component to that trait or characteristic.
Adoption Studies are another important way of disentangling genetic and environmental effects. That is, studying children who were brought up from an early age by parents other than the ones who conceived them (Schaffer, 1996). Adopted children can be compared to their adoptive parents to determine how similar or different they are from each other. If adoptive parents and children are found to be similar to one another than this is likely support for environmental influence (because they do not share genetic material). Adopted children can also be compared to their biological parents (those which they have not been reared by). If biological parents and adopted children share similar characteristics, this lends support to the argument for genetic influences. However, adoption studies are not lacking criticism. Oftentimes 1) biological parents cannot or do not wanted to be located/do not wish to be tested and 2) children who are going to be adopted are often placed with families that resemble or share characteristics with their biological parents (Schaffer, 1996).
Finally, recent developments in the field of Molecular Genetics have allowed for the "investigation of gene-environment interaction in behaviour" (Jenkins, 2006). It is believed that polymorphisms on specific genes may actually make some children more vulnerable than others to negative influences within their environments (Caspi et al., 2002). Levels of symptomatology or psychopathology within individuals are then examined as a function of 1) genetics, 2) the environment, and 3) the combined effects of genetics and the environment, referred to as the 'gene-environment interaction.'
It is interesting however, to examine the history and assumptions behind the twin studies method. Classical twin studies were inspired by the writings of Francis Galton and build upon the family pedigrees studies of eugenicist Abraham Myerson (1925). In the past, family studies demonstrating clustering of particular traits or so-called mental disorders were taken as “proof” of the genetic argument. This search for the culprit genes and demonstration of the inheritibility of psychological traits and disorders continues. The belief in the inheritance of certain psychological traits deemed undesirable is one of the reason thousands of individuals were sterilized without their consent in the 1900s.
One of the main theoretical assumption of twin-studies is that of the “equal environment assumption.” In classical twin-studies examining MZ and DZ reared in similar environment, it is argued that higher concordance rates of a psychological trait or condition in MZ vs DZ demonstrates the genetic basis and inheritibility of this trait or condition. However, MZ share a more similar prenatal and perinatal environment than DZ twins. DZ share the same placenta, they are treated more similarly, they are more often raised as a unit and spend more time together then MZ twins. As a result, it is not possible to completely tease apart the environment from the genetic influence or their interaction. For instance, if a particular disorder is associated with exposure to a toxin in the environment, it is more likely that DZ twins will share similar levels of exposure in comparison to MZ twins. Thus, it is problematic to conclude inheritance based on higher concordance rates of MZ vs DZ twins.
Studies of twins reared apart are also problematic, at least with regard to the pre-natal environment. The role of early bonding and attachment experiences prior to being separated would also need to be taken into consideration given their influence on psychological functioning.