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Considerable parallelism is exhibited by the patterns of variation of infant mortality and maturation rate in human populations. Infant mortality rate is found to be a closer correlate of menarcheal age than estimates of caloric intake, and is considered to reflect improvements in medical care, hygiene, sanitation, workload, and other living conditions as well as nutrition. It is suggested that there has been a change in the modal distribution of energy resources within the individual and not merely an increase in energy supply.