Editors' introduction

Contemporary urban environments in industrialised countries that contain features that impact on human biology and health are represented in this essay that focuses on children. Two approaches to human biologic study are demonstrated: (1) starting with a factor of the urban environment and tracing its effects, and (2) starting with a characteristic of urban populations and seeking the causes of it in the urban physicosocial environment. The analysis of the current asthma epidemic is an example of the latter, and it describes the role that other animals, e.g. cockroach and dust mites, may play in triggering asthma sensitisation and attacks. Although pollution is often included among the new environmental features of cities, rarely are animal allergens considered even though they are pollutants in the strict sense of the term. In an example of the first analytic approach, the effects of low level lead pollution on child development are illustrated with new data from a longitudinal study of infant growth. Just as Ellison's approach in the previous chapter illustrates the importance of measuring putative proximate determinants of ovarian function, the illustrations in this chapter emphasise the measurement of environmental features, whether allergens or lead, and move away methodologically from urban-rural comparisons.