Holistic View on Health: Two Protective Layers of Biodiversity

The western world has witnessed a rising epidemic of chronic inflammatory disorders, such as allergies and asthma. This epidemic is expected to spread also to the rest of the world, where allergies have to date been practically absent, along with adoption of western lifestyle. In parallel, biological diversity is globally declining. This inspired Ilkka Hanski, together with medical doctors, to formulate the biodiversity hypothesis of allergic disease. This hypothesis proposes that reduced contact with natural environments, including natural microbial diversity, is associated with unhealthy human microbiota, less able to educate the immune system. Contact with beneficial bacteria, particularly early in life, seems to be instrumental to the normal development of immune responses. Changes in lifestyle and diet, destruction of natural environments, and urbanisation threaten our natural exposure to these beneficial bacteria and thus also reduce their impact on our physiology. To ensure a healthy life, we need to preserve biodiversity in the environment and make sure it finds a favourable home in us. In this review, we will focus on the role of commensal microbiota in human health and wellbeing, as well as the interaction between our microbiota and environmental microbiota, highlighting the contribution of Ilkka Hanski.