American Scientist

To the Editors:

David Kent’s “Listening to Resveratrol” (September–October 2008) captured my attention. Longevity is a hot topic in the life sciences and has particular relevance to life-history theory. Regardless of resveratrol or other diet additives, the length of human reproductive careers and life spans is constrained by long-term selection pressures. For instance, the human skeleton ages regardless of diet, subsistence pattern, climate and developmental history at a remarkably consistent rate. The skeleton completes maturation between 24 and 30 years, which often corresponds to age at first reproduction in males at least. Although some changes in the joint surfaces of the pelvis occur by about 35 years, young adulthood extends to 49 years when signs of aging start accumulating.

The fact that these changes occur irrespective of local conditions suggests that human aging is a species-specific process that has evolved over millions of years. Similarly, human reproduction is largely consistent cross-culturally, even among males. Age at last birth most often occurs before 40 years in females and before 45 years in males. Although pharmacology and biotechnology may promise perpetual fecundity and increasing longevity, reproduction well into the second half of the fifth decade and the ability of humans to live beyond 120 years will continue to be anomalous unless selection pressures alter growth and reproduction in descendants of those alive today.

Frank L’Engle Williams
Atlanta, GA