Tripartite Phenotype of Aging diagram (IMAGE) University of Southern California Caption The Tripartite Phenotype of Aging is a model describing how genetics, environmental factors, and stochastic, or chance, variations shape longevity. Credit Beth Newcomb, iStockphoto Usage Restrictions Use with credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.