OUR ORIGINS

The foundation for normal adult reproduction is set during fetal life. Sex, as are all other functions, is the product of genetics and the environment working as one informational unit which is so complex that, under normal conditions, their separate contributions cannot be isolated. Prenatal and postnatal development takes place in an environmental context, that is, the combination of the individual's changing milieu and life experience. Epigenetic influences, that are all the external variables which modulate the activity of genes, become more evident the older an individual becomes. Age, education, experience, conditioning and disease all shape appearance, thought, emotion and behaviour. For example, babies look more like each other than do fully formed adults, and genetically distinct adults may have more in common with their peers than with themselves at an earlier age. The process of development starts in the ovaries and testes of the parents where the cells destined to become the future gametes are first differentiated as a distinct germ line and, on fertilization, forge the generational link between parent and offspring.

Since epigenetic effects can be operative at any time during the differentiation of the gametes, the health and living conditions of both parents from the time of gamete formation to the conception of the offspring are crucial, as is the mother's situation during pregnancy (Chapters 8 and 9). There are aspects of early development which, if uncorrected perinatally, may have long-term effects upon the individual. Fetuses have mechanisms by which they adapt to deteriorating environmental conditions brought about by drug abuse, disease, nutritional deprivation and non-adaptive lifestyles.