primarily or only in certain population groups. A related problem is that few of the cited studies include data that represent the whole population of children. Thus, the findings that are reported as significant may be significant only in the population studied or similar populations. Nonetheless, the committee found the evidence to be sufficiently compelling to warrant inclusion when there was a plausible, well-supported connection between the influence and health.

Moreover, inferences about the relative importance of the variety of influences are heavily dependent on the nature of the theoretical models that underlie statistical analysis. If more proximal influences are mixed with more distal ones, they may appear to have stronger effects, even in situations in which more distal factors are operating on a multiplicity of proximal influences and therefore have cumulatively greater effect overall. Thus, future research should adapt more appropriate pathway techniques to help to sort out the patterns by which the influences interact to produce different states of health.

Finally, the relative lengths of the following sections are not meant to signify the relative importance of the influences. For some, the prevalence is less well known than for others. From the viewpoint of influences on population or subpopulation health, the relative frequency of the different influences is at least as critical as the degree of the risk that they pose to individuals. Additional research is needed to refine understanding of the relative contribution of each of the influences and the relevance of each across a variety of social and cultural groups.

CHILDREN’S BIOLOGY

A child’s biology determines how physiological processes unfold and how organ systems adapt to outside influences. Biological response patterns, including responses to stress, novel situations, and primary relationships, can directly and indirectly influence other biological, cognitive (learning), and behavioral processes. The term “biological embedding” has been used to describe how the external environment influences and shapes the biological environment (including the central nervous system), which in turn changes the way the individual interacts with the external environment (Hertzman, 1999).

Genes

DNA provides the blueprint for life. The units of heredity, or genes, are specific sequences of DNA that code for proteins that affect the particular physiology and anatomy of an individual. All cells contain the full array of genes but, depending on the cell type, some are expressed while others are not; for example, certain genes coding for proteins in the retina are expressed in the cells of the eye, but not in the pancreas cells.

Disruptions in genes can be caused by events before, during, or after conception and may produce disorders immediately or later in life. A parent can pass on



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