North American Ed - Brain development

2.1A Genes and environments

From conception on, development is shaped by a melding of genes and the environment. The child is affected by other individuals, available resources and opportunities, and cultural patterns. Because each child is different, children who experience similar environments can have very different outcomes. In turn, children themselves affect their environments.

As discussed in the first section of this module, the nature vs. nature debate is obsolete. Our genetic inheritance is shaped by our experiences — from conception on. Even identical twins, who are genetically the same, have differences. These are shaped by their environments, prenatally and throughout life. In the following video, you will meet identical twins, Brooke and Leah, who tend to approach life differently.

The next reading is also on page 1.1 of this module. You may find it helpful to refer to it again as you consider the information on this page.

In the following video, Dr. Charles Nelson, professor of Pediatrics and Neuroscience at Harvard Medical School, explains how biology (genes/nature) and experiences (environments/nurture) work together to affect development.

Gene by environment interaction

Dr. Marla Sokolowski, co-director of the Child and Brain Development Program at the Canadian Institute for Advanced Research, adds to this discussion of how genes and environment interact by explaining that individuals with different alleles (gene forms) can have different sensitivity to the same environment. She also reminds us to consider positive environmental conditions that promote healthy development rather than focus on negative early experiences.

Gene by environment interaction can be defined as different effects of environmental/ experiential exposure in people with different genotypes or, alternatively, a different genotype effect in those with varying experiential exposures.

The Genetic Science Learning Center at the University of Utah provides a thorough review of genes, DNA, chromosomes and heredity. There is also an explanation of how a person’s genes and environment interact to affect the expression of traits.

Developmental Origins of Health and Disease

While it is tempting to focus on experiences that happen after birth, as we learned in the discussion of brain architecture, prenatal experiences also have a tremendous potential to impact brain development. As proposed by epidemiologist, Dr. David Barker (1995), the fetal origins hypothesis draws our attention to the extreme sensitivity of the fetus to negative environmental factors. Barker noted associations between altered fetal growth from fetal undernutrition in the last half of gestation and coronary heart disease in adulthood. Subsequently, researchers have learned more about the detrimental impact of factors such as poor nutrition and prenatal stress.

The fetal origins hypothesis is currently understood as the developmental origins of health and disease (DOHaD). Listen now as Sir Peter Gluckman explains this evolving field of study.

Dr. Meghan Azad, at the University of Manitoba, expands on the concept of DOHaD and provides examples from her research.

Dr. Azad is the co-director of the THRiVE Discovery Lab at the Children’s Hospital Research Institute of Manitoba. Explore their website to learn more about research projects conducted by members of their interdisciplinary team.

Epigenetics

As we first saw on p. 1.1 in this module, research on epigenetics has made us rethink the relationship between our biological systems and the environment around us and has shown that experience really does get “under the skin”.

The field of epigenetics looks at how environments and experiences can affect the expression of a person’s genes. “The word ‘epigenetics’ consists of the word ‘genetics’ and the Greek root epi, which means upon or over…. The science of epigenetics looks at processes that mark DNA and can change gene expression without modifying the underlying genetic sequence of the DNA” (Sokolowski and Boyce, 2017b, para. 2).

The following reading from the Encyclopedia on Early Childhood Development provides an overview of the topic of epigenetics.

Dr. Meaghan Jones, assistant professor, Department of Biochemistry and Medical Genetics at the University of Manitoba, explains that epigenetics relates to the developmental origins of health and disease (DOHaD) – that what happens early on has implications for lifelong health. She uses a prism model to explain epigenetics and describes how she came up with this model.

In the next video, Jones explains research done with mice to look at how changes to the maternal mouse diet can result in epigenetic changes in the offspring.

At the top of this page, we considered twins Brooke and Leah who, while genetically identical, exhibit different behaviours. Listen now as Dr. Michael Skinner, professor in the School of Biological Sciences at Washington State University, discusses how epigenetics explains the differences between identical twins. This helps us understand that epigenetic changes happen after birth, as well as prenatally.

In the next two videos, Dr. Michael Kobor, professor in the Department of Medical Genetics at the University of British Columbia and Canada Research Chair in Social Epigenetics, explains the lasting effects of epigenetic changes in childhood and some examples of new research being done in this area. Kobor’s explanation of epigenetics helps clarify why experiences in the early years have such a “long reach”.

Sokolowski summarizes the difference between gene by environment interaction (which she explains in her earlier video on this page) and epigenetics. She also reminds us that research in these areas is very new and there are still many questions to be explored.

The next reading is from the Bulletin on Early Childhood Development (2015). It is a brief description of research by Michael Kobor and Joanna Holbrook that looks at individual susceptibility to epigenetic changes.

Emerging research related to epigenetics explores whether epigenetic changes are passed from one generation to another (and beyond). Dr. Moshe Szyf, professor in the Faculty of Medicine and Therapeutics at McGill University, describes some early work underway on this question.

Skinner explains how a serendipitous event in his lab first led researchers to investigate transgenerational inheritance – a form of non-genetic inheritance where epigenetic changes in sperm and egg cells are transferred to subsequent generations.

While this research may underscore the significance of early brain development, it is important to understand that gene by environment interactions and epigenetic effects go beyond early childhood and, in fact, continue throughout life. Furthermore, we now know that some individuals’ genomes are more vulnerable to epigenetic changes in response to the environment and experiences than others. This finding helps explain why only a fraction of people develop post-traumatic stress disorder with the same lived experience, or why some long-term smokers develop cancer while others do not.