Nature and nurture

12/5/03. By Marcus Pembrey

Marcus Pembrey looks at the interplay between genes and environment.

Together, the terms 'nature' and 'nurture' cover all the influences that determine an adult’s constitution – the sum total of their particular physical and behavioural characteristics.

Introduced in his 1874 book, 'English Men of Science; Their Nature and Nurture', Francis Galton commented that "the phrase 'nature and nurture' is a convenient jingle of words, for it separates under two distinct heads the innumerable elements of which personality is composed". He went on to develop the method of comparing the degree of likeness between identical twin pairs with that between fraternal twins as a means of apportioning the contribution of nature and nurture to certain characteristics.

In reality, of course, a separation of the innumerable elements into two distinct heads is not usually possible, except at the extremes, but that did not stop a century of fierce nature versus nurture debates. With one eye on finding something or someone to blame, or wondering how an adverse outcome might be prevented, the questioner asked - is it due to nature or nurture, or more commonly these days, is it genetic or environmental?

The terms 'nature' and 'nurture' cover all the influences that determine an adult's constitution – the sum total of their particular physical and behavioural characteristics.

While the term 'nature' translates into the person's genetic makeup, and 'nurture' into the person's physical, nutritional and psychosocial environment, framing a question specifically in terms of genes or environment is even more removed from reality. It loses the developmental context (implied in the word 'nurturing') in which a person's characteristics emerge as a result of the joint action of both nature and nurture over time. As Matt Ridley's book 'Nature via Nurture' illustrates so well, "[genes] are themselves exquisite mechanisms for translating experience into action". It is not a question of either/or, but both.

Despite emphasising this point, I do not want to imply that research into the relative impact of inherited genetic variation and environmental exposures during development is a sterile pursuit. On the contrary, incorporation of genetic analysis into the study of child development and common disease is a fertile area for research with the prospect of gaining a fuller and more balanced understanding of the causal pathways.

For example, it is well known that maternal smoking during pregnancy is associated with low birth weight in the baby - a clear example of the effects of (mal)nurture - but recent research shows that most of this effect is confined to that half of women who have deficiency variants of two genes, CYP1A1 and GSTT1, involved in the metabolism of toxic compounds in tobacco smoke.

Despite the success in discovering the genes and mutations underlying rare, simply inherited Mendelian disorders, we cannot be so confident about discovering the genetic influences in normal development and assessing the extent to which the differences between people (including their disease susceptibility) can be attributed to differences in the genes they inherited rather than other influences. What we can say with confidence is that the interactions will be complicated. The impact of gene variants is likely to be conditional on the environment.

Twin studies, particularly where the twins have been reared apart, have been valuable in indicating that genetic influences are playing a bigger role in many traits than previously suspected, but in the end the combined effects of genetic variations and environmental pressures on development can only be studied in the general population. Ideally the studies need to follow subjects from early in pregnancy until adult life collecting information on the physical, nutritional and psychosocial environment, with careful measurements of outcomes as well as biological samples for DNA and biochemical analysis.

The Avon Longitudinal Study of Parents and Children (ALSPAC) is such a study based on some 14 000 subjects born in 1991-2 around Bristol. Fetal life is a crucial time for the interactions between nature and nurture, and of course the environment in the uterus stems from the combined effect of maternal genes and exposures, as the smoking example above illustrates.

ALSPAC has already shown that eating oily fish in pregnancy can enhance the visual development of the child, that maternal ingestion of paracetamol in pregnancy can increase wheezing in the child, and that the maternal levels of androgens in pregnancy can influence the way daughters will play in the future. You can be sure genetic variations in the mother, baby or both will be modulating these developmental responses as well. It is the interplay of nature and nurture.

Marcus Pembrey is Director of Genetics within ALSPAC, University of Bristol, and Professor of Paediatric Genetics, Institute of Child Health, University College London.

Further reading

Ridley M (2003) Nature via Nurture. Genes, experience and what makes us human. Fourth Estate.

Wang X et al (2002) Maternal cigarette smoking, metabolic gene polymorphism, and infant birth weight. JAMA 287: 195-202. Abstract

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