When does human longevity start?: Demarcation of the boundaries for human longevity

The scientific debates on the future of human life span and its possible bi ological limits revealed a great need for direct identification of longevit y boundaries, if they really exist. The key question posed in this study is as follows: how can we possibly determine the age when human longevity sta rts? To address this problem, we studied the familial transmission of human life span from parents to daughters, since daughters did not have a high i ncidence of violent causes of death due to military service and are particu larly responsive to parental life span. We found that the familial transmis sion of human life span from mother to daughter is essentially nonlinear wi th virtually no daughter-mother life span resemblance for shorter-lived mot hers (died before age 85) and very high familial resemblance (additive heri tability) for longer-lived mothers. This indicates that maternal age of 85 years could be considered as a demarcation point (lower boundary) for femal e longevity. Women who live above this age are fundamentally (presumably ge netically) different from other women in the sense that their daughters liv e significantly longer. Thus, the age of 85 years could be considered as a threshold age when women mortality becomes much more selective. A similar s tudy of familial transmission of human life span from father to daughter re vealed a demarcation point at 75 years, suggesting that this age might repr esent a lower boundary for male longevity. These results are also consisten t with predictions of the evolutionary theory of aging and mutation accumul ation theory in particular, namely that the additive genetic variance for h uman life span should increase with parental longevity. In other words, hum an mortality should become more selective at advanced ages, and this predic tion is confirmed in the present study.