Human Longevity: Nature vs. Nurture—Fact or Fiction

HUMAN LONGEVITY: NATURE VS. NURTUREFACT OR FICTION BRUCE A. CARNES, * S. JAY OLSHANSKY, f LEONID GAVRILOV, t NATALIA GAVRILOVA, t DOUGLAS GRAHN* In order to be longevous, "select long-lived parents, and particularly longlived mothers."—Raymond Pearl [1, p57] Introduction Some 50 years later, the papers written by the biologist Raymond Pearl still stand as classics in the study of human longevity [1-6]. By attempting to explain how individuals become longevous, Pearl was addressing a question that virtually everyone ponders once old enough to comprehend their own mortality. Traditionally, factors that might influence how long we live have been divided into two general categories: heredity (nature) and environment (nurture). The perceived importance of heredity often depends on one's scientific discipline, and views range from seeing heredity as a primary determinant to considering it no more than a minor contributor Correspondence: S. Jay Olshansky, 400 Springside Lane, Buffalo Grove, IL 60089. Funding for this work was provided by the following NIH/NIA grants and the Center on Aging pilot project program at the University of Chicago (BA. Carnes, 1K02AG00894-01 (NIA), W-31-109-ENG-38 (U.S. Department ofEnergy, Office of Biological and Environmental Research); SJ. Olshansky, 1K02AG13698-01; L.A. Gavrilov, 1R03AG13698-01; NS. Gavrilova , 1R03AG16138-01A1). The authors would like to thank Drs. Fred Stevens and Gayle Woloschak at Argonne National Laboratory and Dr. Michael Fry at Oak Ridge National Laboratory for their valuable comments and suggestions on this manuscript. This manuscript has been created by The University of Chicago as Operator of Argonne National Laboratory ("Argonne") under contract no. 31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. * Center for Mechanistic Biology and Biotechnology, Argonne National Laboratory. tThe Department of Medicine, University of Chicago. ^National Opinion Research Center, University of Chicago.© 1999 by The University of Chicago. All rights reserved. 0031-5982/99/4203-1005$01 .00 422 Carnes et al. ¦ Human Longevity: Nature vs. Nurture—Fact or Fiction to human longevity. Despite a rapidly expanding knowledge base in the biomedical sciences and emphatic claims made about the heritability of longevity, the relative importance of nature versus nurture in determining duration of life remains unresolved. If desire could determine truth, the hope that longevity can be continuously increased through lifestyle modifications and manipulation of the environment within which we live would make nurture the easy winner. Measuring Heritability With the exception of monozygotic twins, every human possesses an assemblage of genes that differs from that of any other human—past or present . Traits like eye color or blood type are heritable because they are genetically transmitted from parent to offspring. The trait of interest in this discussion is human longevity or duration of life. Humans die at virtually every age ofthe known life span, and they live in awider diversity ofenvironments than any other species. Deaths caused by genetic diseases are known to exist. However, there are also causes of death (e.g., accidents, homicide) that almost certainly have little to do (directly) with the genetic makeup of the individuals who die. Scientists interested in human aging want to know how much of the observed duration of life is genetically determined and how much is environmentally influenced. However, the biometricians and geneticists who have developed the theory and methods for estimating heritability do not estimate the heritability of a trait in categorical genetic terms. Instead, they estimate the proportion ofthe variation in the observed distribution of a trait that can be attributed to either genetic or environmental sources. Although the initial question concerning the heritability of human longevity seems simple enough, the approach to answering it is complicated by a scale of measurement—variance—that can be difficult to visualize and interpret. And there are additional complications that are central to understanding the disputes that arise over the issue of heritability. Most of the remaining discussion within this section will be a distillation ofinformation contained within three papers...