Both nature (genetics) and our nurture (environment) substantially affect the development of our mental capital through life:

• An individual’s genetic make-up is determined at conception and remains essentially constant throughout life, although there is growing evidence that environmental factors can have long-term impacts on which genes are expressed and which are silent through processes of “epigenetic” modifi cation. In terms of “broad-sense heritability”, the genetic contribution to cognitive ability has been estimated to rise from well below 50% in childhood to over 60% in adulthood, and is still probably at least this level in old age55.

• However, an individual’s genetic make-up can also affect the mental capital trajectory in far-reaching ways. For example, a gene has been found which is associated with a greatly reduced risk of anti-social behaviour in abused children, suggesting that the gene may confer a degree of resilience56.

• The quality of the home learning environment, including parenting practices such as reading to children, using complex language, and responsiveness and warmth in interactions, are all associated with better developmental outcomes.
  

The health and lifestyle of pregnant women can have important effects via processes that are not presently well understood, but which are often described as “in utero programming”. Here, particularly important factors include maternal diet, smoking and stress, all of which can affect foetal brain development and have a deleterious impact on the baby’s biological systems and cognition. The socio-economic status of the mother is an associated factor, although underlying mechanisms are not well understood.