The Tao of Human Aging

In 1900 the average life span of humans was 47 years old and by 2000 this had increased to approximately 77 years old (Crews 2003). From an evolutionary standpoint this is a tremendous increase in a relatively short amount of time and the process and epidemiological consequences that accompany an aging population are poorly understood. While several animals models have been used to study the effects of aging they are a weak substitute for humans aging with their long periods of adolesence and post-reproductive life history stages as mentioned in a recent article in PLOS Genetics by Martin et al. (2007).

Genetic Determinants of Human Health Span and Life Span: Progress and New Opportunities

George M. Martin^*, Aviv Bergman, Nir Barzilai

We review three approaches to the genetic analysis of the biology and pathobiology of human aging. The first and so far the best-developed is the search for the biochemical genetic basis of varying susceptibilities to major geriatric disorders. These include a range of progeroid syndromes. Collectively, they tell us much about the genetics of health span. Given that the major risk factor for virtually all geriatric disorders is biological aging, they may also serve as markers for the study of intrinsic biological aging. The second approach seeks to identify allelic contributions to exceptionally long life spans. While linkage to a locus on Chromosome 4 has not been confirmed, association studies have revealed a number of significant polymorphisms that impact upon late-life diseases and life span. The third approach remains theoretical. It would require longitudinal studies of large numbers of middle-aged sib-pairs who are extremely discordant or concordant for their rates of decline in various physiological functions. We can conclude that there are great opportunities for research on the genetics of human aging, particularly given the huge fund of information on human biology and pathobiology, and the rapidly developing knowledge of the human genome.

While this article is an excellent review of currently genetic theories of aging it does little in its attempt to explain the evolutionary implications of aging in human populations. Several hypothesis such as the Grandmother Hypothesis have been developed in why humans have such a long life span. While no doubt individuals survived past reproductive age in the past they did not probably do so in large number. Certain Neanderthals lived too a ripe old age such as Shanidar 1 who was between 40-50 years old and certain chimps such as CHETA (who was in the Tarzan movies in the 30s) and is currently 75. However, these are probably the exception rather than the rule. Today the fastest growing non-immigrant segment of the US population are those individuals 85 and older (currently 4.3 million), or as the gerontologists have termed them the oldest old. This is clearly something never experienced before in the evolutionary history of humans. Whereas in the past a few individuals may have survived this far, today a great number of us will reach this age category. As Martin et al. state understanding the underlying genetic mechanisms that allow certain individuals to live longer than others and several of these may have underlying genetic influences. So why do people live longer and are there selective factors influencing the age increase can become an anthropological question as well as a medical and political one. With the baby-boomers about to retire and an impending A(ging) bomb about to detonate it is becoming increasingly important to bring an anthropological perspective to the study of the elderly.

References

Crews D. 2003. Human senescence: evolutionary and biocultural perspectives. Cambridge: University of Cambridge Press. 291 p.