Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes.http://arxiv.org/abs/1103.4649
As a sidenote:
If you haven't heard of the SENS foundation yet you might enjoy hearing about the latest in longevity research.
http://sens.org/sens-research/research-themes/
10 years ago extending human lifespans seemed absolutely impossible, but with the recent clinical trials in humans of stem cells after enormous success in animal tests, and with the advance of safer and safer retroviral gene therapy, and with the discovery of the ability to turn adult stem cells back into embryonic, immortally dividing cells, along with pluripotent stem cell therapies, there is actual hope for significant life extension and rejuvenation (better quality of life.) There's even anecdotal reports of patients undergoing IV stem cell treatment having their grey hair regain color.
There's 300,000 patients who have received IV stem cells in clinical trials (Wiki) but in China and Mexico that number is likely much higher due to the black market.
http://investorstemcell.com/stem-cell-research/chinas-black-market-stem-cells/
