You are what your genes experience
The nature/nurture dilemma has long framed debates about the relative importance of genes and environment on human development. For CIFAR member Clyde Hertzman, who is a professor of population health at the University of British Columbia, the question is far more nuanced. Ongoing research illustrates how, rather than genes being responsible for one job and environmental factors for another, the real story centres around how nature and nurture interact with one another.
Events in the external world can leave biochemical fingerprints on a child’s DNA, changing the course of everything from brain complexity to motor skills – some of the fundamental characteristics of individual identity.
“We’re coming to understand now that early experience gets under the skin,” he says.
That thesis holds enormous implications for early childhood education, parenting techniques and health policy. The phenomenon also suggests that an individual’s genetic make-up is programmed to adapt during the formative early years to both positive and negative external stimuli.
The mechanics of this process involve subtle changes in brain chemistry. When very young children experience things – anything from the soothing sound of a parent’s voice or the screams emanating from a domestic assault – those occurrences are carried into the brain in the form of electrical signals. Stress-inducing experiences are associated with heightened cortisol levels, Hertzman says. These signals create a kind of biochemical “cascade” that can trigger structural and chemical changes to cytosine, one of the four building-block components of DNA. The cascade leaves behind distinctive patterns of a methyl compound, which in turn affects the way these genes will express themselves.
This is “the outside world and DNA talking to one another,” he says.
Animal and early human studies on blood and saliva cells suggest that methylation patterns differ noticeably with exposure to positive and negative stimuli.
“Right now, we’re at the statistical association point,” Hertzman says, noting that researchers thus far have had to infer methylation patterns in brain tissue.
How gene-environment interactions affect children’s development and help shape their identities may be “way upstream,” affecting not only the brain circuits that regulate stress hormones, but also the evolution of the organ systems that manufacture these hormones.
“Preliminary evidence suggests that the capacity of early experience to leave epigenetic marks is greater than with later experiences,” Hertzman says, (although the phenomenon has also been observed among people who have endured profoundly traumatic experiences later in life, including living through the Holocaust).
It may also be the case that these changes are intergenerational, explaining how the effects of trauma can indeed be passed from parent to child.
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Clyde Hertzman
Appointment: Fellow
Institution: University of British Columbia
Clyde Hertzman completed training in Medicine, Community Medicine, and Epidemiology at McMaster University in Hamilton, Ontario, between 1976 and 1985 and has been on faculty in the School of Population and Public Health at the University of British Columbia since 1985. Currently, he is a Full Professor in the department, and holds a Tier 1 CRC Chair in Population Health and Human Development. He is also the Director of the Human Early Learning Partnership (HELP), an interdisciplinary network of researchers from British Columbia’s four major universities that aims to develop new understandings and approaches to early childhood development.
Nationally, Dr. Hertzman is a Fellow in CIFAR’s Successful Societies Program and Experience-based Brain & Biological Development Program. He was the Director of CIFAR’s Population Health Program during its last five-year term from 1998-2003, and was a Fellow in the Human Development Program, which also closed in 2003.
Through his work with CIFAR, Dr. Hertzman has been instrumental in creating a new synthesis which links population health to human development. This is best reflected in the publication of Developmental Health and the Wealth of Nations, a collaborative book containing chapters by the members of CIFAR’s Human Development Program (New York: Guilford Press, 1999). Dr. Hertzman was co-editor, with Daniel P. Keating.
Dr. Hertzman has been involved in many consultancies and scholarly committees. Currently, he is Director of the Global Knowledge Network, Early Child Development for the WHO International Commission on the Social Determinants of Health. He also serves on the Scientific Advisory Board of the Harvard Center for Society and Health; the Steering Committee of the Canadian Population Health Initiative; the Presidential Search Committee of the Canadian Institutes for Health Research; and is a member of the European Science Foundation’s Program on Social Variation in Health Expectancy.
In 1999, he was a consultant to the Federal/Provincial/Territorial National Child Agenda Working Group, and in 1999-2000 served as Chair of the Review Committee on Social Cohesion for the Social Sciences and Humanities Research Council of Canada.
In 2005, the United Way of the Lower Mainland awarded Dr. Hertzman the Dr. Margaret Corbett Early Child Development Award. He was elected a Fellow of the Royal Society of Canada in 2006.