Evolution of ageing - AbsoluteAstronomy.com

Enquiry into the evolution of ageing aims to explain why almost all living things

Life

Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...

weaken and die

Death

Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

with age. There is not yet agreement in the scientific community

Scientific community

The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...

on a single answer. The evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary origin of senescence

Senescence

Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...

remains a fundamental unsolved problem in biology

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

.

Historically, ageing

Ageing

Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...

was first likened to "wear and tear": living bodies get weaker just as with use a knife's edge becomes dulled 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

Second law of thermodynamics

The second law of thermodynamics is an expression of the tendency that over time, differences in temperature, pressure, and chemical potential equilibrate in an isolated physical system. From the state of thermodynamic equilibrium, the law deduced the principle of the increase of entropy and...

was formalized. Entropy

Entropy

Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...

(disorder) must increase inevitably within a closed system, but living beings are not closed system

Closed system

-In physics:In thermodynamics, a closed system can exchange energy , but not matter, with its surroundings.In contrast, an isolated system cannot exchange any of heat, work, or matter with the surroundings, while an open system can exchange all of heat, work and matter.For a simple system, with...

s. It is a defining feature of life that it takes in free energy

Gibbs free energy

In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure...

from the environment and unloads its entropy

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. mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s) exhibited such dramatically different life spans.

History

August Weismann

Friedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin...

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. 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 disavowed his own theory before his life was over.

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 is now experiencing a resurgence because of new empirical evidence as well as new thinking regarding the process of evolution.

Mutation accumulation

The first modern, successful theory of mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

aging was formulated by Peter Medawar

Peter Medawar

Sir Peter Brian Medawar OM CBE FRS was a British biologist, whose work on graft rejection and the discovery of acquired immune tolerance was fundamental to the practice of tissue and organ transplants...

in 1952. His idea was that aging was a matter of neglect. Nature is a highly competitive place, and almost all animals in nature die before they attain old age. Therefore, there is not much reason why the body should remain fit for the long haul - not much selection pressure for traits that would maintain viability past the time when most animals would be dead anyway, killed by predators or disease or by accident.

Medawar's theory is referred to as Mutation Accumulation. The mechanism of action involves random, detrimental mutations of a kind that happen to show their effect only late in life. Unlike most detrimental mutations, these would not be efficiently weeded out by natural selection. Hence they would 'accumulate' and, perhaps, cause all the decline and damage that we associate with aging.

Modern genetics science has disclosed a possible problem with the mutation accumulation concept in that it is now known that genes

Gênes

Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

are typically expressed

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

in specific tissues at specific times (see regulation of gene expression

Regulation of gene expression

Gene modulation redirects here. For information on therapeutic regulation of gene expression, see therapeutic gene modulation.Regulation of gene expression includes the processes that cells and viruses use to regulate the way that the information in genes is turned into gene products...

). Expression is controlled by some genetic "program" that activates different genes at different times in the normal growth, development, and day-to-day life of the organism. Defects in genes cause problems (genetic diseases) when they are not properly expressed when required. A problem late in life suggests that the genetic program called for expression of a gene only in late life and the mutational defect prevented proper expression. This implies existence of a program that called for different gene expression at that point in life. Why, given Medawar's concept, would there exist genes only needed in late life or a program that called for different expression only in late life? The maintenance mechanism theory (discussed below) avoids this problem.

Medawar's concept suggested that the evolution

Evolution

process was affected by the age at which an organism was capable of reproducing. Characteristics that adversely affected an organism prior to that age would severely limit the organism's ability to propagate its characteristics and thus would be highly "selected against" by natural selection

Natural selection

Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

. Characteristics that caused the same adverse effects that only appeared well after that age would have relatively little effect on the organism's ability to propagate and therefore might be allowed by natural selection. This concept fit well with the observed multiplicity of mammal life spans (and differing ages of sexual maturity) and is important to all of the subsequent theories of aging discussed below.

Medawar did not suggest that there were fundamental limitations on life span. Organisms exhibiting negligible senescence

Negligible senescence

Negligible senescence refers to the failure of a few select animals to display symptoms of aging. More specifically, negligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly...

suggest that aging is not a fundamental limitation, at least not in the scale of mammal life span.

Antagonistic pleiotropy

Medawar's theory was further developed by George C. Williams

George C. Williams

Professor George Christopher Williams was an American evolutionary biologist.Williams was a professor emeritus of biology at the State University of New York at Stony Brook. He was best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...

in 1957, who noted that senescence may be causing many deaths, even if animals are not 'dying of old age.' In the earliest stages of senescence, an animal may lose a bit of its speed, and then predators will seize it first, while younger animals flee successfully. Or its immune system may decline, and it becomes the first to die of a new infection. Nature is such a competitive place, said Williams, (turning Medawar's argument back at him), that even a little bit of senescence can be fatal; hence natural selection does indeed care; ageing isn't cost-free.

Williams's objection has turned out to be valid: Modern studies of demography in natural environments demonstrate that senescence does indeed make a substantial contribution to the death rate in nature. These observations cast doubt on Medawar's theory. Another problem with Medawar's theory became apparent in the late 1990s, when genomic analysis became widely available. It turns out that the genes that cause ageing are not random mutations; rather, these genes form tight-knit families that have been around as long as eukaryotic life. Baker's yeast

Baker's yeast

Baker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and bakery products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol...

, worm

Worm

The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...

s, fruit flies

Drosophila melanogaster

Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

, and mice

MICE

-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...

all share some of the same ageing genes.

Williams (1957) proposed his own theory, called antagonistic pleiotropy
Pleiotropy
Pleiotropy occurs when one gene influences multiple phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously...

. Pleiotropy means one gene that has two or more effects on the phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

. In antagonistic pleiotropy, one of these effects is beneficial and another is detrimental. In essence this refers to genes that offer benefits early in life, but exact a cost later on. If evolution is a race to have the most offspring the fastest, then enhanced early fertility could be selected even if it came with a price tag that included decline and death later on. Because ageing was a side effect of necessary functions, Williams considered any alteration of the ageing process to be "impossible."

Antagonistic pleiotropy is a prevailing theory today, but this is largely by default, and not because the theory has been well verified. In fact, experimental biologists have looked for the genes that cause ageing, and since about 1990 the technology has been available to find them efficiently. Of the many ageing genes that have been reported, some seem to enhance fertility early in life, or to carry other benefits. But there are other ageing genes for which no such corresponding benefit has been identified. This is not what Williams predicted. This may be thought of as partial validation of the theory, but logically it cuts to the core premise: that genetic trade-offs are the root cause of ageing.

Another difficulty with antagonistic pleiotropy and other theories that suppose that ageing is an adverse side effect of some beneficial function is that the linkage between adverse and beneficial effects would need to be rigid in the sense that the evolution process would not be able to evolve a way to accomplish the benefit without incurring the adverse effect even over a very long time span. Such a rigid relationship has not been experimentally demonstrated and, in general, evolution is obviously able to independently and individually adjust myriad organism characteristics.

In breeding experiments, Michael R. Rose

Michael R. Rose

Michael R. Rose is a Professor in the Department of Ecology and Evolutionary Biology at the University of California, Irvine. His advisor was Brian Charlesworth. His main area of work has been the evolution of aging. In 1991, he published Evolutionary Biology of Aging exploring a view of the...

selected fruit flies

Drosophila melanogaster

Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

for long life span. Based on antagonistic pleiotropy, Rose expected that this would surely reduce their fertility. His team found that they were able to breed flies that lived more than twice as long as the flies they started with, but to their surprise, the long-lived, inbred flies actually laid more eggs than the short-lived flies. This was another setback for pleiotropy theory, though Rose maintains it may be an experimental artifact.

Disposable soma theory

A third mainstream theory of ageing, the Disposable soma theory, proposed in 1977 by Thomas Kirkwood

Thomas Kirkwood

Thomas Burton Loram Kirkwood CBE is an English biologist who made his contribution to the biology of ageing by proposing the concept of Disposable soma. He is currently a researcher in Newcastle University and heads The Institute for Ageing and Health in its School of Clinical Medical Sciences...

, presumes that the body must budget the amount of energy available to it. The body uses food energy for metabolism, for reproduction, and for repair and maintenance. With a finite supply of food, the body must compromise, and do none of these things quite as well as it would like. It is the compromise in allocating energy to the repair function that causes the body gradually to deteriorate with age.

The term disposable soma came from the analogy with disposable products—why spend money making something durable, if it will
only be used for a limited amount of time?

The disposable soma theory has great appeal because its basis is so sensible and intuitive, but there are arguments against it. The theory clearly predicts that a shortage of food should make the compromise more severe all around; but in many experiments, ongoing since 1930, it has been demonstrated that animals live longer when fed substantially less than controls. This is the caloric restriction (CR) effect, and it cannot be easily reconciled with the Disposable Soma theory. Though by decreasing energy expenditure the damage generated (by free radicals

Radical (chemistry)

Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

for instance) is expected to be reduced and the total energy budget might indeed be reduced, but the investment in repair function might still be relatively the same. But dietary restriction has not been shown to increase lifetime reproductive success (fitness), because when food availability is lower reproductive output is also lower. So CR does thus not completely dismiss disposable theory.

Experimentally, some animals lose fertility when their life span

Maximum life span

Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death.Most living species have at least one upper limit on the number of times cells can divide...

s are extended by CR and some suffer no appreciable loss. Males, for example, typically remain fertile when underfed, while females do not. And, even females present an enigma because their fertility decline is not tightly coupled to their longevity gain. For example, in female mice that are restricted to 60% of a free-feeding diet, reproduction is shut down altogether. But female life span continues to increase linearly right up to the threshold of starvation - around 30% of free-feeding levels.

A difficulty with the disposable soma theory is that the energy required for maintenance and repair would appear to be relatively minor when compared to the energy required for gestation (repair should take less energy than producing an entire new organism). Yet gestating animals seem able to perform the maintenance while post-reproductive animals do not. A similar difficulty is that male animals seem to have similar life spans as females despite the apparently higher energy requirement for gestation and other reproductive activities.

Impact of new evolution concepts on ageing theories

At the time most of the non-programmed ageing theories were developed there was very little scientific disagreement with classical theories (i.e. Neo-Darwinism

Neo-Darwinism

or modern evolutionary synthesis

Modern evolutionary synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...

) regarding the process of evolution. However, in addition to suicidal behaviour of semelparous species (not handled by the classical ageing theories) other apparently individually adverse organism characteristics such as altruism

Altruism

Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...

and sexual reproduction

Sexual reproduction

Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...

were observed. In response to these other conflicts, adjustments to classical theory were proposed:

Various group selection
Group selection
In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....

theories (beginning in 1962) propose that benefit to a group could offset the individually adverse nature of a characteristic such as altruism
Altruism
Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...

. The same principle could be applied to characteristics that limited life span and theories proposing group benefits for limited life spans appeared.

Evolvability
Evolvability
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.In order for a biological organism...

theories (beginning in 1995) suggest that a characteristic that increased an organism's ability to evolve could also offset an individual disadvantage and thus be evolved and retained. Multiple evolvability benefits of a limited life span were subsequently proposed in addition to those originally proposed by Weismann.

Ageing theories based on group selection

Mitteldorf proposed a group benefit of a limited life span involving regulation of population dynamics

Population dynamics

Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...

. Populations in nature are subject to boom and bust cycles. Often overpopulation can be punished by famine or by epidemic. Either one could wipe out an entire population. Senescence is a means by which a species can 'take control' of its own death rate, and level out the boom-bust cycles. This story may be more plausible than the Weismann hypothesis as a mechanistic explanation, because it addresses the question of how group selection

Group selection

In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....

can be rapid enough to compete with individual selection.

Libertini also suggests benefits for adaptive ageing.

Inversely, within a Negative Senescence Theory R.D. Lee (similarly J.W. Vaupel) considered positive group effects performing a selection force directed to survival beyond the age of fertility. Often also postreproductive individuals make intergenerational transfers: bottlenose dolphin

Bottlenose Dolphin

Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...

s and pilot whale

Pilot whale

Pilot whales are cetaceans belonging to the genus Globicephala. There are two extant species, the long-finned pilot whale and the short-finned pilot whale . The two are not readily distinguished at sea and analysis of the skulls is the best way to tell the difference between them...

s guard their grand-children; there is cooperative breeding in some mammals, many insects and about 200 species of birds; sex differences in the survival of anthropoid primates tend to correlate with the care to offspring; or an Efe

Efe

The Efe were the leaders of Turkish irregular soldiers and guerillas from the Aegean Region of Anatolia, called the Zeibeks and Kızan. There are many theories about the origins of the word Efe....

infant is often attended by more than 10 people. Lee developed a formal theory
integrating selection due to transfers (at all ages) with selection due to fertility.

Ageing theories based on evolvability

Goldsmith proposed that in addition to increasing the generation rate and thereby evolution rate a limited life span improves the evolution process by limiting the ability of older individuals to dominate the gene pool

Gene pool

In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...

. Further, the evolution of characteristics such as intelligence and immunity may specially require a limited life span because otherwise acquired characteristics such as experience or exposure to pathogens would tend to override the selection of the beneficial inheritable characteristic. An older and more experienced but less intelligent animal would have a fitness advantage over a younger more intelligent animal except for the effects of ageing.

Skulachev has suggested that programmed ageing assists the evolution process by providing a gradually increasing challenge or obstacle to survival and reproduction and therefore enhancing the selection of beneficial characteristics. In this sense ageing would act in a manner similar to that of mating rituals that take the form of contests or trials that must be overcome in order to mate (another individually adverse observation). This suggests an advantage of gradual ageing over sudden death as a means of life span regulation.

Weissmann's 1889 ageing theory was essentially an evolvability

Evolvability

Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.In order for a biological organism...

theory. Ageing or otherwise purposely limited life span helps evolution by freeing resources for younger, and therefore presumably better adapted individuals.

Ageing mechanism concepts

If organisms purposely limit their life spans via ageing or semelparous behaviour, the associated evolved mechanisms could be very complex just as mechanisms that provide for mentation, vision, digestion, or other biological function are typically very complex. Such a mechanism could involve hormones, signalling, sensing of external conditions, and other complex functions typical of evolved mechanisms. Such complex mechanisms could explain all of the observations of ageing and semelparous behaviours as described below.

It is typical for a given biological function to be controlled by a single mechanism that is capable of sensing the germane conditions and then executing the necessary function. The mechanism signals all the systems and tissues that need to respond to that function by means of organism-wide signals (hormones). If ageing is indeed a biological function we would expect all or most manifestations of ageing to be similarly controlled by a common mechanism. Various observations (listed below) indeed suggest the existence of a common control mechanism.

It is also typical for biological functions to be modulated by or synchronized to external events or conditions. The circadian rhythm

Circadian rhythm

A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

and synchronization of mating behaviour to planetary cues are examples. In the case of ageing seen as a biological function, the caloric restriction effect

Calorie restriction

Caloric restriction , or calorie restriction, is a dietary regimen that restricts calorie intake, where the baseline for the restriction varies, usually being the previous, unrestricted, intake of the subjects...

may well be an example of the ageing function being modulated in order to optimize organism life span in response to external conditions. Temporary extension of life span under famine conditions would aid in group survival because extending life span combined with less frequent reproduction would reduce the resources required to maintain a given population.

Theories to the effect that ageing results by default (mutation accumulation) or is an adverse side effect of some other function are logically much more limited and suffer when compared to empirical evidence of complex mechanisms. The choice of ageing theory therefore is logically essentially determined by one's position regarding evolutionary processes and some theorists reject programmed ageing based entirely on evolutionary process considerations.

Maintenance theories of ageing

It is generally accepted that deteriorative processes (wear, other molecular damage) exist and that living organisms have mechanisms to counter deterioration. Wounds heal; dead cells are replaced; claws grow.

A non-programmed theory of mammal ageing that fits with classical evolution theory and Medawar's concept is that different mammal species possess different capabilities for maintenance and repair. Longer lived species possess many mechanisms for offsetting damage due to causes such as oxidation, telomere shortening, and other deteriorative processes that are each more effective than those of shorter lived species. Shorter lived species, having earlier ages of sexual maturity, had less need for longevity and thus did not evolve or retain the more effective repair mechanisms. Damage therefore accumulates more rapidly resulting in earlier manifestations and shorter life span. Since there are a wide variety of ageing manifestations that appear to have very different causes, it is likely that there are many different maintenance and repair functions.

A corresponding programmed maintenance theory based on evolvability

Evolvability

suggests that the repair mechanisms are in turn controlled by a common control mechanism capable of sensing conditions such as caloric restriction and also capable of producing the specific life span needed by the particular species. In this view the differences between short and long lived species are in the control mechanisms as opposed to each individual maintenance mechanism.

Summary of empirical evidence favouring programmed ageing

Existence of complex programmed death mechanisms exist in semelparous species (e.g. octopus) including hormone signalling, nervous system involvement, etc. If a limited life span is generally useful as predicted by the programmed ageing theories, it would be unusual for an octopus to possess a more complex mechanism for accomplishing that function than a mammal.
Discovery of "ageing genes" with no other apparent function.
Caloric restriction effect: reduction of available resources increases life span. This behavior has a plausible group benefit in enhancing the survival of a group under famine conditions and also suggests common control.
Progeria
Progeria
Progeria is an extremely rare genetic condition wherein symptoms resembling aspects of aging are manifested at an early age. The word progeria comes from the Greek words "pro" , meaning "before", and "géras" , meaning "old age"...

and Werner syndrome
Werner syndrome
Werner syndrome is a very rare, autosomal recessive disorder characterized by the appearance of premature aging....

are both single-gene genetic diseases that cause acceleration of many or most symptoms of ageing. The fact that a single gene malfunction can cause similar effects on many different manifestations of ageing suggests a common mechanism.
Although mammal life spans vary over an approximately 100:1 range, manifestations of ageing (cancer, arthritis, weakness, sensory deficit, etc.) are similar in different species. This suggests that the deterioration mechanisms and corresponding maintenance mechanisms operate over a short period (less than the life span of a short-lived mammal). All the mammals therefore need all the maintenance mechanisms. This suggests that the difference between mammals is in a common control mechanism.
Life span varies greatly among otherwise very similar species (e.g. different varieties of salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

3:1, different fish 600:1) suggesting that relatively few genes control life span and that relatively minor changes to genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...

could cause major differences in life span—suggests common control mechanism.

Problems with programmed aging theories

Contrary to the theory of programmed death by aging, individuals from a single species usually live much longer in a protected (laboratory, domestic, civilized environment) than in their wild (natural) environment, reaching ages that would be otherwise practically impossible. Also, in majority of species there doesn't exist any critical age after which death rates change dramatically as intended by the programmed death by aging theory, but the age-dependance of death rates is very smooth and monotonic. In fact, the death rates at extreme old ages start to slow down, which is the opposite of what would be expected if death by aging was programmed. From an evolutionary point of view, having genes that would not result in a programmed death by aging would displace genes that cause programmed death by aging as individuals would produce more offspring in their longer lifespan and they could increase the survival of their offspring by providing longer parental support.

Biogerontology considerations

Theories of aging affect efforts to understand and find treatments for age-related conditions (see biogerontology):

Those who believe in the idea that aging is an unavoidable side effect of some necessary function (antagonistic pleiotropy or disposable soma theories) logically tend to believe that attempts to delay aging would result in unacceptable side effects to the necessary functions. Altering aging is therefore "impossible" and study of aging mechanisms is of only academic interest.
Those believing in default theories of multiple maintenance mechanisms tend to believe that ways might be found to enhance the operation of some of those mechanisms. Perhaps they can be assisted by anti-oxidants or other agents.
Those who believe in programmed aging suppose that ways might be found to interfere with the operation of the part of the aging mechanism that appears to be common to multiple symptoms, essentially "slowing down the clock" and delaying multiple manifestations. Such effect might be obtained by fooling a sense function. One such effort is an attempt to find a "mimetic" that would "mime" the anti-aging effect of calorie restriction
Calorie restriction
Caloric restriction , or calorie restriction, is a dietary regimen that restricts calorie intake, where the baseline for the restriction varies, usually being the previous, unrestricted, intake of the subjects...

without having to actually radically restrict diet.

External links

Evolutionary Theories of Aging and Longevity
The Evolutionary Theory of Aging by João Pedro de Magalhães.
Programmed-Aging.Org Site provides comprehensive information on programmed ageing, the programmed/non-programmed controversy, and underlying evolution controversies.
How Evolutionary Thinking Affects People's Ideas About Aging Interventions
AnAge Animal Ageing and Longevity Database Provides maximum observed ages and sexual maturity ages for many animals.
The Case for Programmed Mammal Aging Describes empirical data, evolutionary rationale, and historical perspective supporting programmed ageing in mammals.
Life Table for USA 2005 Probability of death as a function of age

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