| 翻訳と辞書 |
| Evolution of ageing ： ウィキペディア英語版 |
Evolution of ageing
Enquiry into the evolution of aging aims to explain why almost all living things weaken and die with age. There is not yet agreement in the scientific community on a single answer. The evolutionary origin of senescence remains a fundamental unsolved problem in biology.
Historically, ageing was first likened to "wear and tear": living bodies get weaker, shoes get wrecked with use or, with exposure to air and moisture, iron objects rust. But this idea was discredited in the 19th century when the second law of thermodynamics was formalized. Entropy (disorder) must increase inevitably ''within a closed system'', but living beings are not closed systems. It is a defining feature of life that it takes in free energy from the environment and unloads its entropy as waste. Living systems can even build themselves up from seed, and routinely repair themselves. There is no thermodynamic necessity for senescence. In addition, generic damage or "wear and tear" theories could not explain why biologically similar organisms (e.g. mammals) exhibited such dramatically different lifespans. Furthermore, this initial theory failed to explain why most organisms maintain themselves so efficiently until adulthood and then, after reproductive maturity, begin to succumb to age-related damage.
==History==
August Weismann was responsible for interpreting and formalizing the mechanisms of Darwinian evolution in a modern theoretical framework. In 1889, he theorized that aging was part of life's program because the old need to remove themselves from the theatre to make room for the next generation, sustaining the turnover that is necessary for evolution.〔 Work that describes Weismann's theory about making room for the young.〕 This theory again has much intuitive appeal, but it suffers from having a teleological or goal-driven explanation. In other words, a ''purpose'' for aging has been identified, but not a ''mechanism'' by which that purpose could be achieved. Aging may have this advantage for the long-term health of the community; but that doesn't explain how individuals would acquire the genes that make them get old and die, or why individuals that had aging genes would be more successful than other individuals lacking such genes. (In fact, there is every reason to think that the opposite is true: aging ''decreases'' individual fitness.) Weismann later abandoned his theory.
Theories suggesting that deterioration and death due to aging are a purposeful result of an organism's evolved design (such as Weismann's "programmed death" theory) are referred to as theories of programmed aging or adaptive aging. The idea that the aging characteristic was selected (an adaptation) because of its deleterious effect was largely discounted for much of the 20th century, but a theoretical model suggests that altruistic aging could evolve if there is little migration among populations.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「Evolution of ageing」の詳細全文を読む
スポンサード リンク
| 翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|