We provide food for thought on some pressing questions about health inequalities – why some of us maintain good health into old age, and the inequity of infectious and Non-Communicable Diseases, both very relevant now to COVID-19. We use historical perspectives and modern examples to discuss the population explosion, social determinants of health and how development over the first 1,000 days influences later health. Some ideas are likely to be quite novel to the reader, such as the risk of disease being increased by ‘mismatch’ between our developmental environment and where and how we live later. This takes the story across the globe, from high- to low-income countries, where early development is often less healthy but economic progress is changing environments fast. Can young people in such settings escape, or has the anvil on which their bodies were forged in early life left them with unalterable inequalities? We ask who needs to ‘own’ these problems and why solutions to them have been slow to emerge. The wider, global perspective, sets the scene for the final chapter which focuses on what we can all do as individuals now that we know some of the secrets of our first 1,000 days.