Exposure to unpleasant, uncontrollable, and unpredictable events are unavoidable aspects of life that can cause stress. In humans and other animals, chronic activation of an individual’s stress response systems – particularly in early life – can be costly, leading to poorer health and shorter life expectancy. There is also evidence that stress can be socially transmitted between individuals, with recent experimental work in a songbird (zebra finch) showing that the negative health consequences of early-life stress can be transmitted from an individual to their reproductive partner, almost like an infection. Specifically, early-life stress reduced the lifespan of the individual that experienced it as well as the lifespan of their reproductive partner who had not experienced early-life stress themselves. As these birds lived in benign laboratory environments, well-established mortality risk factors such as disease, starvation and predation could not explain why early-life individuals and their partners suffered accelerated ageing and premature death. Despite these findings, previous experimental studies on early-life stress have focused almost entirely on the exposed individuals and overlooked how early-life stress in an individual can affect the health and longevity of other individuals, particularly partners involved in long-term social relationships. Yet we know that social relationships are significant predictors of human mortality regardless of age, sex, and cause of death and one of the most important predictors of human health and well-being (being as strongly associated with health and longevity as smoking, blood pressure, obesity, physical exercise and other well-established health risk factors). Therefore, this project set out to generate novel insights into the largely unexplored question of how lifespan reduction caused by early-life stress is transmitted to other individuals (i.e. reproductive partners), thus shifting the focus of research on early-life stress, social interactions, and health beyond the level of the individual. The objectives of the project have been met, although the data collected during the project are still being analysed.
