The Interplay Between Genetics and Environment

Psychologists and theorists have long debated the issue of nature (one’s biological traits) versus nurture (the role in the environment in shaping learning) in terms of children’s development. Consistent with the image of the child as a blank slate or empty vessel, behaviorists such as Skinner and Pavlov contended that children could be conditioned in specific ways or taught particular behaviours if positive actions were reinforced and negative ones punished. The environment, of which adults are a part, is certainly central to the child’s development. However, maturationist theorists such as Gesell and Lorenz have argued that one’s genetic inheritance determines development therefore development unfolds according to a specific timetable or biological plan. So, when examining the school achievement of young Jacob, behaviorists might state that he does well because his parents started to read to him when he was a baby or work with him on his homework each night. In contrast, theorists adhering to a maturationist perspective might note that both of his parents are doctors or that he has inherited his mother’s brains.

More recently, Shonkoff and Phillips (2000) established that it is nature through nurture that determines the path of development; genetics establish a foundation for the developing brain and then the child’s experiences and environment interact with genes to shape the brain.

This environment is defined broadly as follows:

The influence of nurture consists of the multiple nested contexts in which children are reared, which include their home, extended family, child care settings, community, and society, each of which is embedded in the values, beliefs, and practices of a given culture (p. 23).

As Shonkoff and Phillips (2000) describe, the ways in which children respond to their environment are partly dependent on inherited dispositions to respond to and interpret these influences. Parents, family members, teachers, and other important adults in the child’s life are the most powerful environmental influences as they have the capacity to create “goodness of fit” with the child’s individual inherited dispositions. Moreover, they argue that biology is “modified by life experience” (p. 389).

Shonkoff and Phillips (2000) note that twin and adoption studies have formed the basis of our current understanding of this dynamic interplay between nature and nurture, though they have some limitations. Since identical twins have the same genetic makeup, a proponent of nature would theorize that they should develop in the same way. However, this has not been found to be the case because each twin has unique experiences and interactions with parents and other important individuals, which correspondingly shapes their development in distinctive ways. If you have a sibling, for example, you might be able to point to some of the variable ways in which your caregivers related to you as compared to your brother or sister. Adoption studies allow researchers to examine the impact of environment or nurture by comparing traits of the child to their biological parent (to whom the child is genetically related but does not share an environment) as well as to their adoptive parent (with whom the child shares an environment, but not genes).

Brain Architecture and Neural Pathways

Beginning about ten weeks after conception, the brain produces neurons at the rate of 4000 a second and by 28 weeks individuals have between 50 and 100 billion neurons which is close to the amount we have as adults (McNeil 2009). These neurons are commonly referred to as “the building blocks of the brain” and they are responsible for storing and transmitting information to other parts of the brain. Dendrites are found on one end of each neuron and these tentacles or branches act as receptors, accepting messages from other neurons. Messages then travel through the neuron, aided by axons, which form the middle of the neuron. Axons are coated in myelin or a fatty white matter. Myelin not only allows the messages to move faster, but Klingberg (2013) has established that it is positively correlated with the development of cognitive function. His research team found that children with a thicker myelin sheath demonstrated improvement in tests of working memory and reading comprehension. Myelin production continues well beyond the prenatal period (Shonkoff and Phillips 2000). There are also terminal buttons at the ends of the axon that release neurotransmitters or chemicals to ensure that messages can be passed from the axon of the one neuron to the dendrites of another neuron. Finally, there is always a space between one neuron and the next called a synapse. McNeil (2009) describes the release of neurotransmitters across the synapse where they bind with receptors on the receptive neuron as the closest possible to “the actual point of learning” (p. 19). This process allows for the creation of neural pathways enabling the transfer of messages through the brain and to other parts of the body.

Every new experience that a child has operates to form and strengthen these neural pathways. The first neural pathways to be formed are the less complex, but very important pathways, for vision, sound, touch, and breathing. As these experiences are repeated, the child strengthens the neural pathways until they are wired or sculpted into the architecture of the brain. In contrast, if neural pathways are not being used or are weak, they will be pruned away. One common metaphor used considers the brain to be a tree and the neural pathways to be branches. Language development provides an illustrative example of how this process functions. Cognitive scientist Patricia Kuhl has described infants as “citizens of the world” as they are born with the capacity to distinguish the speech sounds between every language. Imagine that young Daniela’s parents speak English and Spanish respectively so she consistently hears these languages. In terms of our tree, the “branches” or pathways for these languages grow and become stronger as her exposure to them is repeated through interactions with family members. However, the branches for all other languages are pruned away as she does not have the opportunity to hear them. This pruning does not mean that she has lost the ability to learn those languages in the future. It simply signifies that she is no longer a citizen of the world but rather has become a “culture bound listener” attuned to the languages of the important people in her life. This research affirms the importance of maintaining home languages.

It was once believed that the first three years represented the “windows of opportunity” for optimal brain development because much of the brain’s architecture is shaped in these early years. However, while the early years support the development of basic brain function such as sight and hearing, regions of the brain develop into adulthood (Harvard Centre on the Developing Child, 2018). Klingberg (2013) notes that the hippocampus (critical for long-tern memory) matures fairly early as the pruning process is complete between the ages of five and eight, while the prefrontal cortex matures until one’s early twenties. The teen years have recently been found to assume critical importance in terms of brain development for this reason. It is now understood that we can always form new neural connections even as adults due to the plasticity of the brain. Research on the subject of brain plasticity demonstrates that the brain is not rigid and fixed, but rather is malleable and flexible. Dr. Norman Doidge (2007) writes that scientists: “showed that children are not always stuck with the mental abilities they are born with; that the damaged brain can often reorganize itself so that when one part fails, another can often substitute; that many “circuits” and even basic reflexes that we think are hard wired are not” (p. xix). One of the many examples Doidge provides explains the case of a young woman born without a left hemisphere in her brain. Her right brain learned to take over some of the left-brain functions such as speaking, reading, writing and math. The brain does lose plasticity as we age, but as adults, brain plasticity is a mechanism which allows us to learn new concepts, skills, and information. For instance, as adults we can still learn a new language, though perhaps not with the same facility or degree of fluency as we might have when we were children.

Early childhood policy documents have often used brain development research to argue in favour of funding, programming, and interventions to ensure that all children have access to “quality” experiences. Research on brain development, and particularly the idea that the early years are a critical period, has frequently been cited to justify what Heydon and Iannacci (2009) deem to be a biomedical approach to learning and development. This approach prioritizes specific experiences as being optimal for brain development and children who do not have access (or have limited access) to these experiences are viewed as being unable to develop to their full potential. Heydon and Iannacci (2009) state that when children are seen as neurologically impaired in such a way, they may be pathologized as at-risk or vulnerable. Targeted interventions may be implemented in order to offset these perceived deficits. Undoubtedly the early years deserve our attention and funding, but it is problematic to form the broad assumption that the absence of certain experiences will negatively impact a child’s development.

Stress, Trauma, and Development

Like adults, children experience a variety of stressors in their everyday lives. These may include common experiences such as a conflict with a sibling or peer, going to school for the first time, writing a test, or difficulties completing a task. Jensen (2008) contends that such minor to moderate stressors are positive when the child actively desires to solve the problem, has the ability to do so, perceives that they have some control over the situation, is able to rest between challenges, and can brainstorm possible solutions. These forms of stress are generally fairly predictable as well as productive as they aid children in building the capacity to respond to issues (Perry, 2001). Research has found that moderate levels of stress can ease the process of storing and retrieving memories. In contrast, Jensen explains that when children experience chronic stress or distress, they feel threatened by a physical or emotional danger, a problem that they experience repeatedly and intensely, cannot envision a solution to, lack the resources to resolve, have no sense of control over, and perceive the risks to be too high. As Perry (2001) has described, when a child is exposed to a traumatic situation, the brain activates adaptive responses to ensure survival. The first is a hyperarousal response, commonly referred to as ‘fight or flight’ or elevated state, and the child may exhibit defiance, resistance, aggression, anxiety, or panic. In the second, dissociative, if the threat is inescapable then the body is preparing to protect the child from possible injury by disengaging, avoiding, disassociating or withdrawing into a fantasy world. In many cases, the child will employ some combination of hyper-arousal and dissociative responses.

When children experience a traumatic event such as the loss of a loved one or an accident, they seem to recover once their circumstances change (Shonkoff and Phillips, 2000). However, if a child’s stress response systems are repeatedly activated in this manner as in cases of domestic violence or abuse, the brain has no opportunity to recover which leads to corresponding changes in its functionality (Kingberg, 2013). The repetitive release of the hormone cortisol affects the production of new nerve cells in the hippocampus which, in turn, influences the immune system, local memory and indexing, and perception (Jensen, 2008; Kingberg, 2013). According to Klingberg (2013) the existing neurons also become stunted in the prefrontal cortex. Perry explains that the baseline for the child’s state of arousal is altered to such an extent that they remain in a state of “fight or flight” even when there is not external threat. While the adaptive responses—hyperarousal and dissociation---may aid the child in coping with chaos and unpredictability, they create disadvantage in the classroom context as the child can escalates into a “flight or fight” state when confronted by even small stresses. Jensen (2008) notes that this state of hyper-vigilance allows the child to survive, but not to effectively remember and process information. Children experiencing chronic stress are more susceptible to illness, lower serotonin levels (which may be a risk factor for violent and aggressive behaviour).

Trauma not only influences the development of those who experience it, but also has been found to have residual effects passed from generation to generation. When traumatic events or historic oppression are not adequately addressed, it can have long-term implications for future generations. For example, as late as 1996 Indigenous children in Canada were compelled to attend residential schools where they suffered traumas such as separation from their families, cultural and linguistic genocide, and sexual, physical, and emotional abuse. While indigenous children today have not attended these schools, the intergenerational effects have been devastating to Indigenous families and communities. If parents experience abuse or other forms of trauma in childhood, for example, they may find it difficult to form secure, healthy attachments with their own children.

Sources:

Doidge, N. (2007), The Brain that Changes Itself, New York: Penguin.Harvard University Center on the Developing Child (2018), ‘Brain Architecture’. Available online: https://developingchild.harvard.edu/science/key-concepts/brain-architecture/ (accessed 23 January, 2019).

Heydon, R.M. and L. Iannacci (2009), Early Childhood Curricula and the De-Pathologizing of Childhood, Toronto, ON: University of Toronto Press.

Jensen, E.P. (2008), Brain-based Learning: The New Paradigm of Teaching (2nd ed.), Thousand Oaks, CA: Corwin Press.

Klingberg, T. (2013), The Learning Brain: Memory and Brain Development in Children, New York: Oxford University Press.

McNeil, F. (2009), Learning with the Brain in Mind, London: SAGE.

Perry, B.D. (2013), Brief Reflections on Childhood, Trauma and Society. Houston, TX: The ChildTrauma Academy Press.

Shonkoff, J. P., and D. A. Phillips (2000), From Neurons to Neighborhoods: The Science of Early Child Development, Washington: National Academy Press.