In this fourth and final episode of series Why Am I? the message is clear — events we endure in our childhoods have long-lasting effects on the rest of our lives, both physically and mentally. The Dunedin Study explores nature versus nurture, deciphering the differences in people's biology, physiology, and mental states through the lens of differing experiences and socio-economic backgrounds. New discoveries show how abnormal inflammation as an adult may be due to a lonely childhood, potential ways to minimise the effects of schizophrenia, and how having a pet may help keep you allergy-free.