A child's natural temperament may affect his physiological response to stress, according to new research from the University of Rochester, New York.

In attempting to contribute to the evolutionary understanding of the biological impact of chronic stress, scientists hypothesized that the association between changes in children's cortisol levels in reaction to parental conflict is moderated by the youngsters' innate temperaments.

Cortisol is a naturally-occurring hormone which is produced by the adrenal gland in response to stress or a perceived threat. It is a biological response intended to protect the individual by increasing blood sugar, suppressing the immune system and affecting metabolism. Triggering a 'fight or flight' response, the sudden increase in cortisol provides a quick energy boost, improved memory and a higher pain tolerance intended to maximize survival. Cortisol levels are generally regulated throughout the day, with most people secreting higher levels in the mornings and lower amounts at night. Consistently elevated levels of the steroid hormone, however, are associated with negative physical consequences including high blood pressure, weakened immune system and reduced cognitive performance.

Hawks Versus Doves

In the study , researchers recruited 201 two-year olds from underprivileged families and low socio-economic backgrounds who had been exposed to elevated levels of aggression between their parents. Researchers assessed the participants' exposure to parental aggression through interviews and questionnaires with the children's mothers. Because ongoing and repeated exposure to parental fighting causes significant stress to children, evaluating this group can provide insight into the relationship between stressors and biological responses and can provide possible explanations for the evolution of different personality types.

The toddlers were exposed to several unfamiliar settings and to a simulated, mildly-stressful, parental telephone argument. They were classified as 'hawks' or 'doves', based on their reactions, with hawks defined as tots who demonstrated aggressive coping strategies and fearlessness towards new environments. Conversely, those who responded to the same tests by clinging to their mothers, crying or demonstrating submissive and passive reactions were labeled doves.

Aggressive Kids with Parents Who Constantly Fight Can't Deal with Stress

Results revealed distinct cortisol levels among the two groups of toddlers after their exposure to the simulated argument between their parents. The children who responded with heightened vigilance and inhibition to that parental aggression had higher cortisol levels, while the hawks, or toddlers with aggressive temperaments, showed marginally diminished cortisol reactions.

Researchers noted associations between the two groups' biological reactions and markers for behavioral and emotional problems. Significant increases in cortisol production were related to lower attention problems but greater risk of developing anxiety or depression among the doves. The hawks' lower cortisol levels were associated with a reduced likelihood of developing anxiety problems but a greater likelihood of risky behavior and attention and hyperactivity problems.

Researchers noted that the divergent biological responses may have correlated with unique survival benefits and disadvantages for our ancestors, prompting lead author Patrick Davies, professor of psychology at the University of Rochester, to suggest that the findings provide a counter-argument to the idea that there may be more than one effective way of being.

The study was published online in the July issue of Development and Psychopathology.

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