Natural environments and mental health

Ancestral experiences and evolutionary processes continue to influence the brain in ways that may escape conscious awareness by contemporary adults. It is becoming increasingly evident that the 2.2 million years our genus has spent in natural environments are consequential to modern mental health. This might be especially true in the context of rapid global urbanization, loss of biodiversity and environmental degradation. Here, we examine some of the emerging research related to natural environments (and specific elements within them) and mental health. Our synthesis includes research from various branches of science and medicine, e.g., epidemiology, psychology, physiology, anthropology, evolutionary biology, and microbiology. Significant knowledge gaps remain. However, the accumulating strength of research from multiple disciplines makes it difficult to dismiss the clinical relevancy of natural environments in 21st century mental health care.