while genetic factors play an increasingly larger role at advanced ages, environmental, social, and behavioral factors influence survival patterns much more heavily at younger ages. Although twin studies that focus on the correlation in age-at-death have yielded important insights into the role of genetics in human lifespan, the determinants of human survival patterns are immensely complex and change with age-i.e. While studies of extreme longevity clustered within human families have indicated at least some genetic role in determining lifespan at very advanced ages, twin studies, which offer the opportunity to disentangle the genetic and environmental factors for a given trait, indicate genetic factors are responsible for only a modest amount of the variation (20–30%) in human lifespan and that the role of genetic factors is minimal before age 60, but increases thereafter. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist.ĭue to the social and economic consequences of variation in human lifespan there is considerable interest in identifying the extent of social, environmental, and biological determinants of survival patterns in humans. įunding: This work was supported by grant R21AG046760-01 from the National Institute on Aging. Data from the Human Mortality Database are accessible at. Instructions on how to apply and a link to the data request application form can be found here. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: The Danish Twin Registry is a public register administered in accordance with Danish law and the DTR makes data available to researchers after they have applied and their project has been approved by the DTR Scientific Board. Received: Accepted: ApPublished: May 18, 2016Ĭopyright: © 2016 Sharrow, Anderson. PLoS ONE 11(5):Įditor: Calogero Caruso, University of Palermo, ITALY While existing research suggests an increasingly important role for genetic factors at very advanced ages, we conclude that the social closeness of monozygotic twins is a plausible driver of the survival advantage at ages <65.Ĭitation: Sharrow DJ, Anderson JJ (2016) A Twin Protection Effect? Explaining Twin Survival Advantages with a Two-Process Mortality Model. We find intrinsic processes confer a survival advantage at older ages for males, while at younger ages, all monozygotic twins show a health protection effect against extrinsic death akin to a marriage protection effect. We examine this survival advantage by fitting these data with a two-process mortality model that partitions survivorship patterns into extrinsic and intrinsic mortality processes roughly corresponding to acute, environmental and chronic, biological origins. Using data from the Danish Twin Registry and the Human Mortality Database, we show that monozygotic twins have greater cumulative survival proportions at nearly every age compared to dizygotic twins and the Danish general population. Twin studies that focus on the correlation in age-at-death between twin pairs have yielded important insights into the heritability and role of genetic factors in determining lifespan, but less attention is paid to the biological and social role of zygosity itself in determining survival across the entire life course.
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