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Evolution of aging:Why do we get old and die?

September 11, 2010

There are “eternal fundamental questions” in life.

What will happen to us after we die?

What is the meaning of life?

Are we alone in the universe?

Why do we get old and die?” is one of these questions. To answer this question,  evolution scientists had a lot to say on the causes behind aging and death.

Evolution immediately brings into mind a name and a concept; Charles Darwin and natural selection. Natural selection is simply about nature’s selection of the traits and its bearers in favour of survival and reproduction of the species. Therefore, it is not surprising that the evolutionary approach to uncover the mystery behind aging has been critical.

August Weismann (1834–1914)

Weisman has been the father of evolution of aging theories. Prior to  his work in late 19th century, the general belief on the causes of aging relied on “wear and tear” theory. According to this historical theory we were getting older just as a knife’s edge becomes dulled with exposure to air and moisture.

Programmed death theory

He  explained aging as a programmed process in the organism for the needs of species. The old should leave, so there would be room for the younger. His theory, however, lacked practical evidence.

Peter Medawar (1915 – 1987)

Mutation Accumulation Theory of Aging

In the following century, Medawar put the work of Weismann and that of others together and proposed an exciting and interesting theory. According to Medawar aging was simply a by-product of natural selection. For example, the genes involved in fixation of bones in young age were in favour of survival and reproduction. In older ages, however, these genes would not be beneficial and the older would have bone fractures as a result. According to Medawar, natural selection declined by age and youth had a cost to pay; aging.

George C.  Williams (1926- September 8, 2010)

The antagonistic pleiotropy theory of aging

Williams took Medawar’s theory further. He suggested that one particular gene not necessarily would have effect on one trait of the organism but rather on different traits (pleiotropy).  The natural selection would be in favor of the young compared to the old.  These genes will be maintained by nature as they will be beneficial at young age, but will be deleterious at older age. That is why his theory is also called as “Pay Later” theory.

William Hamilton (1936–2000) and Brian Charlesworth (1945- ) later proved these theories mathematically.

Many species have been investigated in the field of evolution of aging, but by far the most popular has been a fruit fly; Drosophila melanogaster (Greek, dark-coloured belly). It has been practical to use them as it is easy to take care of them, the breed quickly by laying many eggs. Researchers were able to delay aging in Drosophila by only allowing older flies to reproduce. Although the results of some studies with Drosophila fruit fly favour Medawar’s theory of mutation accumulation rather than Williams’s antagonistic pleiotropy hypothesis, conflicting results also exist.

Interview with Prof. Charlesworth on evolution

We have a life span longer than our ancient ancestors. Will the average life span of the human past the age of 100? If so, what will the mechanisms be? The evolution theorists will tell us more in the future thanks to the scientists mentioned above and many others.

Suggested Reading

Evolution of ageing since Darwin

The Evolutionary Theory of Aging

Evolutionary Theories of Aging and Longevity

Aging is not Senescence: A Short Computer Demonstration and Implications for Medical Practice

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