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Ageing


Contents

Origin of Ageing
Ageing Process and Symptoms
Causes
Reliefs
Anti-ageing Research

Origin of Ageing

Ageing is usually defined as the progressive loses of biological function accompanied by decreasing fertility and increasing mortality with advancing age. This process usually occurs after sexual maturation and continues up to the time of maximum longevity (life span) for members
Life Span Bio-longevity of a species. Death is the final event. Roughly speaking life span of an organism is proportional to its size -- bacteria may only live for a few hours, an insect a few days, and an elephant for years. Figure 01a shows that there is considerable deviation from a linear relationship, and Figure 01b displays many exceptions including the primitive sea anemone, which can survive up to 70 years. Signs of senility, or extreme old age, are seldom seen in the wild. Animals living under natural conditions rarely approach their maximum possible age because of very high death rates due to infant mortality, diseases, predators, bad weather, accidents, or competition for food and shelter. For this reason, most of the reliable information about the length of the life span comes from the zoos.

Figure 01a Life Span[view large image]

Figure 01b Bio-longevity[view large image]

The evolution of lifespan for different species is explained by the classic models of reproductive schedules, which address adaptive trade-offs between number of offspring, initial age of reproduction, reproductive senescence and age-group mortality. For example, experiments on fruitflies, possums and guppies indicate that predatory pressure can accelerate reproduction at the apparent expense of longevity.
    There are three theories on the origin and evolution of ageing. They are not mutually exclusive. The combination actually provides a consistent hypothesis.

  1. Mutation Accumulation - As mentioned above, most animals in the wild do not have the opportunity to reach senescence. Natural selection has no chance to operate on a wide range of alleles with late deleterious effects. They are allowed to accumulate over the generations with little or no check. Thus, the problems with senescence occurs only in modern human or animals in the zoos within an environment, where "life expectancy" of living organisms have been artificially extended. Life expectancy is the average (over the population) total number of years (or days, or hours) that an organism expects to live. It is fundamentally different from life span, which is the maximum time interval that an organism can live.
  2. Antagonistic Pleiotropy - This theory suggested that pleiotropic genes with good early effects would be favoured by selection even if these genes had bad effects at later ages, i.e., a small beneficial effect early in life can outweight a late deleterious effect even if the latter results in senescence and death.
  3. Disposable Soma - This theory suggests that organism will benefit by investing any spare resource into reproduction or survival, rather than into better repair capacity, even though this means that damage will eventually accumulate to cause ageing.
As mentioned in the sub-topic of "Sex and Death", when unicelluar bacteria practised asexual reproduction by fission, they were essentially immortal. The appearance of ageing began when single-cell eukaryotes started sexual reproduction by exchanging genetic materials in the micronucleus, the old macronucleus became redundant and withered away. Multicelluar organisms carried the process further by segregating the germ cells from the somatic cells, which are disposable in contrast to the germ cells, which seem to be immortal. The catch is that the genetic make-up of the new germ cells is different from the previous generation; it is not an exact copy of the old one. And asexual reproduction cannot carry on forever either; it is susceptible to environmental stress. So nothing can live forever.

Since plants are autotrophs (self-nourishment) living on inorganic materials and adopt to a sedative life style, some of them can afford to invest most of their resource into maintenance having life span up to 5000 years. While the annual (1 year), biennials (2 years), and perennials (3 years +) plants bloom for a long time investing their resource in reproduction; many species of trees live to hundreds and thousands years old with a
Moss Campion Bristlecone Pine very short blooming time (see Table 01 for a list of some North American trees, range is from average to maximum). In particular, even the low laying Moss Campion (classified as dicots not moss, Figure 02a) can live up to 350 years, the Bristlecone Pine (Figure 02b) is the champion with age up to 5000 years. However, it is rara that a tree will get to live out its full, natural lfie span. Infestation and external damage frequently take its toll since they cannot move to avoid intrusion or attack.

Figure 02a Moss Campion [view large image]

Figure 02b Bristlecone Pine [view large image]


Life Span of Plants

Table 01 Life Span of Some North American Trees


Pleiotropy means one gene determines two different characteristics.

See the 2 documents on "Theories of Aging" and "Evolutionary Theories of Aging and Longevity".

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