The new theory, proposed by Ronald D. Lee, Ph.D., of University of California, Berkeley, suggests that natural selection favors animals capable of devoting energy and resources to insuring survival of the next generation. After birth, all mammals including primates, all birds, many insects and some fish nurture their offspring. Post-reproductive bottle nose dolphins and pilot whales, for instance, babysit, guard and even breastfeed their grandchildren. And in certain primates, the gender that provides the primary care to offspring tends to have a higher life expectancy. This suggests that nurturing behavior and longevity evolved together over time.
The hypothesis appears in the Proceeding of the National Academy of Sciences Online Early Edition the week of July 14, (doi:10.1073/pnas.1530303100). This work was supported by the National Institute on Aging (NIA), part of the National Institutes of Health and the U.S. Department of Health and Human Services.
"This theory offers a fresh look at how longevity and nurturing behavior may have evolved and challenges many pre-existing ideas about the nature of aging. It is an important concept that opens the door to new ways of thinking about longevity," says Richard Suzman, Ph.D., Associate Director of the NIA for the Behavioral and Social Research Program.
According to previous theory, since the primary evolutionary goal of any species is propagation, natural selection against aging and mortality weaken once an organism begins to reproduce, and its remaining fertility declines. Weaker selection leads to generalized deterioration and aging. But this theory has several flaws, Dr. Lee says. It doesn't account, for instance, for extended post-reproductive survival, juvenile mortality falling with age, and the evolution of low levels of fertility combined with heavy investment in the nurturing of offspring. The new theory attempts to fill in many of these gaps.