Secular Trends in Stature, Weight, and Maturation

Human biologists use the term to refer to alterations in human beings over long-time periods. These changes may be positive, that is, increases or accelerations, or they may be negative. A positive change is not necessarily favorable. By their nature, secular trends are due almost entirely to environmental variations. Genetic drift affecting a is, indeed, a secular trend but is not considered in this review. If genetic changes occur in a local due to migration, studies of the population before and after the migration may show differences, but the is not the same. This pitfall must be avoided when data spanning several decades from a particular locale or institution are analyzed, as, for example, the study by Vines (1904) comparing the statures of boys attending a given school in 1874 and in 1901. The area served by the school or the racial affiliations of those attending the school may have changed considerably. Despite their importance for many purposes, such comparisons are unsatisfactory for the study of secular trends. There are other methodological considerations. For example, when comparisons are made between studies, can we be certain both groups of workers measured in the same way? Whether or not stature was recorded to the nearest millimeter, the nearest centimeter, or the last-completed centimeter makes a difference. Was weight measured nude in both studies? If the children were weighed wearing light indoor in both surveys, the weight of this clothing may differ. Probably such clothing is considerably lighter now in developed countries than was the case 100 years ago. Age may present a problem. Were ages verified from birth certificates and, just as important, were they reported clearly? As discussed later, some