Biodiversity, microbes and human well-being

The biodiversity hypothesis postulates that the rapid increase in the prevalence of allergies, asthma and other chronic inflammatory disorders in developed countries in the past few decades is caused by loss of biodiversity, which reduces human exposure to beneficial environ- mental microbes with essential immunoregulatory functions. The biodiversity hypothesis builds upon Graham Rook's 'old friends' concept, which highlights the long-term evolution of the human immune system with a diverse assembly of microbes. I describe a case study showing that the inci- dence of atopy (allergy sensitization) in adolescents decreases significantly with an increasing amount of forest and agricultural land in the surroundings of their homes. Environmental micro- biota as part of broader biodiversity provides a tangible but little appreciated 'ecosystem service', which is vital for every individual.