Life-Span Extension - Evolution Of Longevity
Evolution of longevity
After the end of the reproductive period, an organism, be it mouse or human, can no longer contribute to the evolutionary pool in any sort of direct way, so there is little reason to think that evolution would select for individuals who live well past the age of reproduction. Moreover, since most organisms in the wild die from infection, accident, or predation, most scientists working on aging think that there is no selection for a program that kills an organism. Genes that regulate longevity also function to do other things as well, and their effects on longevity are thought to be secondary to these other actions. A small, but very vocal, subgroup disagrees strongly with this view, arguing that aging is genetically programmed. One of the best arguments against genetic programming is that no one has been able to eliminate the aging program in any species. In other words, no immortal organisms have been found, and most scientists think that they never will be. Other processes sometimes associated with aging are programmed, including programmed cell senescence, also called the Hayflick limit, and programmed cell death (apoptosis). These processes can be completely eliminated in the lab, but no one has turned a mortal organism into an immortal one.
Ben Bova was right about one thing—all people have the potential to be immortal. To be more precise, one part of each person has that potential: the germ line. Obviously, one part of the human must in some sense be immortal or human life would not exist today. However, the indefinite life of the germ line does not mean that any biological component in the process is really immortal. The somatic part of the germ line wears out; men accumulate mutations in their sperm, and women go through menopause. Menopause is not something that is unique to humans; numerous other species also show a cessation of reproduction in females late in life. Numerous arguments have been put forward arguing that menopause provides advantages to humans over evolutionary time periods, but there is little direct support for this notion and certainly no need that it be true. Modern medical interventions have already extended the reproductive life of women into their sixties using a variety of in vitro fertilization technologies and appropriate hormone treatments.
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