The tails of survival curves.

This article focuses on the occasional individuals of many species that live longer than is usual for their populations--here called longevity outliers. They appear to be exceptions to the usual patterns of mortality rates that increase with age. There is no model of survivorship that accommodates all of these individuals. They are less vulnerable to the usual causes of death than most in their populations. There are hints of genetically based mechanisms in the form of life-prolonging genes in invertebrates and genetic resistance to fatal diseases in higher organisms. The reasons why longevity outliers ultimately die are not known. Based on well-established trends, I predict that there will be many more humans reaching very old ages in the next century.