The Developing Developmental Biology of Childhood Adversity
Research over the last century has shown — unsurprisingly — that social hardships in early life can cause enduring health problems. A common example is poor nutrition, clearly a link between childhood poverty and adult illness. A related, heartening puzzle: how do some kids manage to thrive despite such socioeconomic disadvantages?
Cutting-edge studies in animal biology are shedding new light on a major reason why. That is, the development of biology and behavior is driven by gene-environment interactions. The upshot is that individuals are not affected equally by tough conditions. These individual differences arise from the interplay between an organism’s inherited traits and its surroundings. The classic notion of “nature versus nurture” is thus rendered obsolete.
The tricky part is how to go about understanding the role of individual variation in organisms’ responses to their environments. These dynamics are notoriously difficult to study and predict. Variation in numerous genes, operating in hyper-diverse environments, leads to complex interactions. Teasing apart the relationships demands sophisticated analyses, including experimental approaches not possible in human research. In this way, studies of other species are identifying mechanisms for the health impacts of early social stress.
For example, macaque monkeys reared without their mothers develop emotional abnormalities, such as poor social skills and aggression. Recent experiments show that the response to those adverse conditions depends on individual variation within a gene. The gene is linked to production of a protein involved in brain function, and in mediating responses to stress, anxiety and depression.
Studies of simple model animals take this work further, enabling actual gene manipulation. Fruit fly experiments show how chronic food deprivation at the larval stage interacts with natural variation in a gene that controls foraging. The early adversity then influences adult exploratory behavior. This willingness to investigate is essential for finding food — in mammals it is also critical for development of independence and mate selection. The poor nutrition in flies also affects eventual reproductive output, the ultimate index of a stressor’s impact.
Collectively, such studies show that some genotypes may be more sensitive to environmental conditions than others. That means individuals can experience different behavior and health outcomes in response to the same conditions.
This research into the “developmental biology of social adversity” is an important advance in studying the health impact of early life conditions. Conventional approaches tend to miss the point that many interacting factors underlie most health problems. Important questions in this emerging field include how the strength, timing, and duration of early life adversity influence development, and how interventions might alter health outcomes.
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