Near all of the discussion on human aging and longevity that takes place even nowadays, in this age of revolutionary progress in biotechnology, is characterized by a profound lack of ambition. People think about aging and wisely nod their heads and say things like "we should focus on our lifestyle choices" so as to marginally alter the outcome of disability and death. This is disappointing on many levels. It seems that the majority gravitate to tinkering with what is, to doing easy things simply because they are easy, rather than trying in earnest to change matters for the better. The best lifestyle choices in the world will still lead to a 75% mortality rate by age 90: the only way to do better is the creation of new medical technologies, such as the SENS vision of periodic repair of the known forms of cellular and molecular damage that cause aging.
Here is one example of failing to reach far enough: a post on a new longevity blog that glances at the present range of theories of aging, and then concludes that we should focus on lifestyle and environment because that is what we have control over now. It is disappointing to see this sort of response from someone who has actually looked into the science.
By knowing a little about why we age, we can begin to understand the things that we can and can't change about the process. Exerting control in certain areas of our lives, can give us the best chance to lead a longer, healthier, and happier life. There are many theories that offer an explanation of why human beings grow older. It has even been claimed that there are over 300 current hypotheses that attempt to explain aging. Space precludes a full evaluation of all perspectives, but in very general sense the main ideas can be summarized as evolutionary, biological, and wear-and-tear perspectives.
The evolutionary theories of aging suggest that natural selection has optimized the fitness of individuals only until they have conceived and reared children. Beyond middle age, it is theorized that evolution is essentially blind to the fate of individuals as by this time they are likely to have already passed on their genetic material and successfully raised their offspring to the point at which they can fend for themselves. In evolutionary terms, the work of life is done.
The biological theories of aging contend that there are inherent limits within our physiology that constrain individual lifespan. Theorized processes include limits in the number of times that certain cells can divide, the increasing potential for random mutations in the body, and the tendency for bodily systems to become increasingly unreliable over time. These perspectives suppose that we are ruled by the rhythm of a biological clock, which will tick, tick, tick until the main spring loses its charge and we expire.
The rate-of-living and wear-and-tear theories of aging are concerned with the accumulation of damage in the human body that results from either normal bodily functions (such as respiration and the conversion of food into energy that produces free radicals and oxidative damage) or the impacts of negative lifestyle behaviors and exposure to certain environmental conditions. Lifestyle factors that can influence aging are many and include exposure to UV radiation, smoking, body composition (proportion of body fat), exposure to chemicals and pollutants, mechanical injury or overuse, and others. It is in the realm of lifestyle and environment that we have the greatest hope of healthy life extension because these tend to be the domains over which we have the greatest control.