The emergence of intelligence and discernment in our thinking brain provided a degree of autonomy in forward planning, tool-making, imitation and teaching. Acquisition of sophisticated language made it possible to understand mental states in others, which helped in the creation of a unique hominid social, political, economic, ethical and spiritual order. This chapter describes normal development and how epigenetic influences (that is, all the environmental variables which modulate gene activity) might derail it. Harmful epigenetic influences can trigger intrinsic gene defects (mutations) or adversely modify normal gene expression, resulting in impaired growth and development. Good health, far from being a natural state or universal right, is a matter of achievement, a consequence of privilege or good luck even. It is for this reason that health is defined in the Constitution of the World Health Organization (WHO) as being a state of ‘complete physical, mental and social wellbeing, not merely the absence of disease or infirmity’. This definition succinctly emphasizes the positive aspects of a fully realized genetic potential. Good health can, therefore, be seen as the result of a positive environment supported by socioeconomic advantage. This and the subsequent two chapters are concerned with ways that everyone can improve – maximize – their own and their children's genetic potential. Very few of us come close to fully expressing our genetic potential, but with increased biological understanding we can move closer to enjoying our innate distinctive capabilities.