A nine-year study of wild monkeys in Thailand has uncovered a critical window during early pregnancy when maternal stress can permanently alter their offspring’s ability to handle life’s challenges – with implications that may extend to human health and development.
Scientists tracking Assamese macaques in Thailand’s Phu Khieo Wildlife Sanctuary found that exposure to elevated stress hormones during the first half of pregnancy was associated with lasting changes in offspring’s stress response systems, persisting well into adulthood. The research, published in Proceedings of the Royal Society B, provides rare insights into how early-life conditions shape long-term health outcomes in nature.
What makes this finding particularly striking is that these effects don’t require major traumatic events – even moderate environmental pressures like food scarcity or social tensions during early pregnancy can trigger lasting physiological changes in offspring.
Unlike controlled laboratory studies, this research observed animals facing real-world challenges in their natural habitat. Over nearly a decade, researchers repeatedly collected and analyzed fecal samples from pregnant females to measure their exposure to various environmental stressors.
“Our results show that the HPA-axis activity of offspring was enhanced, the more adversity the mother had experienced during early pregnancy – which could be food shortages or social conflicts for example,” explains Simone Anzá, lead author of the study and former doctoral student at the University of Göttingen and the German Primate Center.
The timing of the stress exposure proved crucial. The study revealed that elevated maternal stress hormones in late pregnancy or during nursing did not produce the same effects as exposure during early pregnancy, when organs are first developing.
Previous analysis from the same research had already demonstrated that early prenatal stress was linked to altered growth patterns and negative changes in gut microbiome composition, suggesting these early influences can affect multiple body systems simultaneously.
“Our research results indicate that the timing of maternal stress hormone exposure during and after pregnancy crucially affects the consequences for the development and health of the offspring,” notes Oliver Schülke, who led the study at the University of Göttingen and the German Primate Center.
The research team’s detailed analysis revealed that only about 2% of growth rings showed stress-related changes in both pine trees and juniper shrubs. However, these changes were particularly concentrated in specific years that aligned with known environmental events.
These findings could have important implications for human health, as similar biological mechanisms are at work across primates. Understanding how and when maternal stress affects development could help medical professionals better target preventive care during pregnancy.
The research suggests that paying special attention to maternal well-being during early pregnancy – both physical and psychological – might be particularly important for offspring health. “Our findings may help to identify the timing and mechanisms that preventive measures should address in order to reduce long-term health risks,” Schülke adds.
The study’s unique approach of examining these effects in wild populations, rather than laboratory settings, provides a more complete picture of how environmental stressors influence development under natural conditions. This real-world context helps scientists better understand the subtle yet significant ways that early-life experiences shape long-term health outcomes.