Every single organism matures and ages, it appears to be a pre-programmed part of being. Naturally, humanity concerns itself with many questions, and aging theories are in part science and part philosophy/sociology. Science helps us to understand what is aging. We hope to influence its pace and reverse aging altogether if possible. Eternal youth ought to be the end goal but we do not know if that is achievable. For now, we use science to slow down aging until methods of extending life indefinitely become feasible and affordable.
Theories of aging are evolving as we speak. There is no concrete consensus amongst the scientists who study it as to the cause of aging. The science behind it is relatively recent and research into aging raises further questions. Perhaps someday we will know for certain the causes of aging and how to counter growing old effectively. Immortality and eternal youth are theoretically possible, but not yet within reach, it is the ultimate goal. Support this site to accelerate reaching that goal. With your support, we can review more scientific research to formulate a better, far-reaching model.
What is aging?
Aging could be summarized as a biological process. Humans go through several stages where our bodies behave differently, most of us are familiar with birth, infancy, childhood, puberty, middle age, and decline. Whether we start aging in the womb or after puberty is also unclear. In short, there are far more questions than answers. However, we will attempt to address all questions here to create a coherent heuristic model of aging for you to take into account when making decisions about introducing changes in your lifestyle to extend your lifespan and health span.
Genetic theory suggests that we age the fastest in the womb and in childhood, but there are a few overlapping theories.
Gerontology – the science of age and age-related disease.
Scientific research into the aging process is called gerontology, it concerns itself with the biological process of aging and the socially-attributed factors of advanced age. Gerontology is further divided into sub-fields of social gerontology and biogerontology.
Social gerontology
Social gerontology assesses how the aging population impacts society and the social aspects of growing old for individuals such as reduced mobility. Improving the understanding of the difficulties of the life of seniors is researched by social gerontologists. It is difficult to imagine the feeling of being old and fragile for those who have not approached the later stages of life. Emerging technologies such as robotics may one day be of massive help in looking after the aging population.
Biogerontology
Biogerontology is the sub-field of gerontology concerned with the biological aging process, its evolutionary origins, and interventions in the process such as introducing changes to the lifestyle to increase longevity. It is not just the increased life span that interests biogerontologists but also increases the health span. Years of extended life ought to be fun and active as opposed to years being full of suffering.
A deeper, more specialized field of biomedical gerontology, also known as experimental gerontology or clinical gerontology and life extension, is endeavoring to slow, prevent, and even reverse aging in both humans and animals.
In reality, however, most science has a role to play in the fight against aging.
Current scientific discourse on aging
Geroscience, biogerontology, and most research with the root geron (geron means old man in Greek) look at ways to extend and improve quality of life.
Three key questions in regard to the science of aging:
Is aging a disease?
Is aging an evolutionary necessity?
Is decline at an advanced age a pay-off for rapid body development in the womb, infancy, childhood, and puberty?
Biogerontologists may argue that aging is a disease by definition and should be treated directly, with the ultimate goal of having the chance of individuals dying independent of their age (if external factors are held constant).[1][2][3] Others may argue that the maximum life span can not, or should not, be altered.
To summarise, gerontologists would prefer you to die in skiing accidents or of physical exhaustion after sexual marathons at the age of triple digits instead of less exciting ways earlier.
Geriatrics
In this way, biogerontology is different from geriatrics, which is a field of medicine that studies the treatment of existing diseases in seniors, rather than the treatment of aging as a disease. Ultimate success in the fields of biogerontology will eliminate dying from age-related diseases, which in turn will make geriatrics an obscure science of little relevance.
Theories of aging
There are distinct theories of aging each with its merits and criticisms. Some may be in conflict with others but overall, despite the spectrum – we can divide them into two categories
Program vs errors
At their extremes, the diversity of aging theories can be split into bio-programmed theories – which imply that aging follows a natural timetable, and error theories – which suggest aging is a result of cumulative and exponential damage experienced by living organisms and accompanying inability to repair the damage [4].
Order vs entropy
Another way to distinguish the theories is into order which views aging as a natural process necessary for species to be replaced by more adapted specimens and entropy where fragile organisms accumulate malfunctioning cells which results in the inability to function [??]
In computing, it is common to analyze a digital creation in terms of features vs bugs. This can be applied to natural organisms as well and it is worth mentioning that aging can be both a feature and a bug simultaneously. Perhaps aging is necessary for the development of a child rather than something separate organisms experience through later life.
Stochastic theories
Stochastic theories presume an occurrence of a variable process where the outcome involves some randomness and some uncertainty, but the result is predictable. In terms of aging, this means that growing old is caused by a tide of tiniest changes in the body over a long time and the body’s failure to restore the parts of the system to their original healthy state. In the process, the body becomes less capable of repairing the damage the body. Cells and tissues are impaired due to the accumulation of damage over time resulting in further diminished functioning of organs until the point where the body ceases to be functioning altogether. The idea of gradually accumulated damage was first introduced in 1882 by biologist Dr. August Weismann as the “wear and tear” theory.[5][6] Since the discovery and decoding of DNA, this can also be applied to DNA damage.
Wear and tear theories
Wear and tear theories of aging were voiced centuries ago. To summarise:
- As organism ages, its parts such as cells and organs wear out from continued use. Like a clock where from constant usage, even the strongest materials suffer damage over time.
- Wearing out the body can be attributable to internal or external causes that eventually lead to an accumulation of errors that surpass the capacity for restoration.
- Due to these internal and external impairments, cells lose their ability to regenerate, which ultimately leads to biomechanical and chemical exhaustion which hinders further repairs, a knock-on effect.
- Things that hurt our bodies such as harmful chemicals in the air, food, or smoke hurt us by occupying existing repair mechanisms. Viruses, physical and mental trauma, free radicals, and unnecessary inflammation also drain resources that could have been used to repair cells otherwise.
Accumulation theories
Accumulation theories of aging suggest that aging is an accumulation of harmful or waste elements, from both internal and external sources. [7]
Mutation accumulation theory
British-Brazilian biologist, Peter Medawar put forward the mutation accumulation theory in 1952 [8] as an evolutionary explanation for biological aging and the associated decline of the elderly.
- The theory proposes that most harmful mutations are only expressed later in life as a reproductive function has been exhausted and future survival is increasingly unlikely.
- Then, as there are no more offspring, these mutations are likely to be passed on to future generations.
- Medawar posited that over time these mutations would accumulate due to genetic drift and lead to the evolution of what is now referred to as aging.
Free radical theory
Free radicals are unstable molecules that can damage the cell membrane which makes the cell more susceptible to irreversible damage, causing cellular disruption and DNA breaks in turn.
The free-radical theory of aging states that this kind of damage accumulates over time, eventually leading to a degradation of cell function across a range of cellular components such as fat, proteins, or DNA which leads to aging. [9] It was suspected that free radicals are harmful and the theory combined the ideas of Rebeca Gershman in the mid-1940s [10] and was furthered by Denham Harman a decade later. So we’ve known about free radicals for a while, allowing time to study them. Denham Harman demonstrated how free radical reactions damage cells. [11]
How do free radicals harm your body?
- A reactive molecule is roaming around the body until it comes into contact with a structure such as a receptive cell membrane.
- An electron transfer damages the cell and this is known as oxidative stress.
- Free radicals damage accumulates over time
Reactive oxygen species are a subset of free radicals and they consist of many oxygen-containing molecules. Unlike water which has an oxygen atom and is considered to be neutral, these molecules are highly reactive.
Sources of free radicals
- Natural metabolic processes in the body
- A side-effect of a body fighting against disease
- Ionizing and ultraviolet radiation such as sun rays.
The role of antioxidants s to neutralize free radicals, however, free radicals are also used in the organism to indicate a problem, so neutralizing the oxidants before the problem is handled is not recommended. Some time ago as this theory of aging was popular antioxidants became a fad but now high doses of antioxidants are considered to be harmful. There still is a multibillion-dollar antioxidant industry out there, which is, unfortunately, discredited to a large degree.
DNA damage theories
Recently DNA damage has become the center of attention for the anti-aging crowd. DNA damage has been put forward by scores of scientists as being the lead cause of aging.
DNA or Deoxyribonucleic acid is a relatively resilient molecule, it is two strands, double helix, we’ve all seen the pictures.
Taking into account that we can extract neanderthal DNA and even attempt to clone mammoths from DNA that has been preserved for thousands of years – it is sturdy. However, due to a whole range of problems DNA can be miscopied into new cells and then further miscopied until it becomes a problem. For DNA to be of any use it has to be stable.
DNA is incredibly stable, considering that it consists of billions of lines of chemical code. Every cell division is a marvelous process but errors can be made. Millions of cells are replaced every day, and naturally these errors, despite the robustness of the genome, will accumulate.
How do errors happen?
Environmental factors such as hostile agents, free radicals, disease, and viruses, can all destabilize the genome and break the strand.
The broken genome is then replicated and the replica is deformed/erroneous.
The cells that are replicated give rise to new erroneous cells.
Your body will try to defend itself against DNA breaks by sending signals but not all deformed cells will be repaired/destroyed. If the body’s defense mechanisms are distracted by other things, the repairs might not actualize. Sometimes the errors are too far gone and the cells have divided and multiplied in their damaged state too much. Sometimes deformed cells refuse to die. This is how you get cancer. Our bodies deal with cancerous cells continuously because if you have billions of cells – eventually some of those errors will be missed by our body’s defenses. Continuous accumulation of miscopied or copying of damaged cells is what the DNA damage theory of aging is all about.
DNA Damage is different from mutation, despite both being errors. The question of whether DNA damage with or without mutations causes aging is still open, so perhaps even without mutations – the cell replication process of damaged cells impacts aging. The hypothesis was developed soon by physicist Leó Szilárd.[25] T
The stability of the genome is defined by the cells’ machinery of repair, damage tolerance, and checkpoint pathways that counteracts DNA damage. One hypothesis proposed by physicist Gioacchino Failla in 1958 is that damage accumulation to the DNA causes aging.[24] The hypothesis was developed soon by physicist Leó Szilárd.[12] This theory itself took on new views in due time and further study into DNA proved that this theory is feasible. New types of DNA damage and mutations are being looked into by scientists, however, there is still a lot of uncertainty [13][14]
Difference between DNA damage and DNA mutation
The genome is a robust entity however it suffers from damage nonetheless. The key difference between DNA damage and DNA mutation is in the kind of damage.
Cells containing DNA have natural defenses such as cell membranes.
Occasionally the chemical structure of the cell will undergo stress that will damage its integrity which will lead to DNA damage.
The DNA sequence may occasionally miscopy itself, a minor change perhaps, small enough for the body’s defenses to ignore it so the cells replicating further will be of mutated DNA.
There is no reason for DNA damage and mutation not to occur simultaneously, in any case, we should prop up our bodies so that either is unlikely to occur on a large scale.
If the damage is substantial, this may accelerate aging, evidence from studies on mice and humans that looked into DNA and cell deficiency found that DNA damage is linked to faster aging.[15][16].
Is DNA damage the main reason for aging?
There appears to be a correlation when comparing species of different life expectancies. As a hypothesis, DNA damage should correlate with lifespan, and the ability to repair should be persistent for longer in longer-living species. Studies have shown that there is indeed a correlation across mammalian species of the relationship between nucleotide excision repair and life span in multiple studies. [17]
Cross-linking theory
The cross-linking theory is somewhat related to DNA damage and DNA mutation. The theory proposes that advanced glycation end-products (stable bonds formed by the binding of glucose to proteins) and other aberrant cross-links (bond or a short sequence of bonds that links one polymer chain to another) accumulate over time in tissues and is the cause of aging. These bonds crosslink proteins which disable or impair their biological functions. This leads to the hardening of the connective tissue, kidney diseases, and enlargement of the heart are connected to the cross-linking of proteins. The knock-on effect on DNA is further detrimental to health, as DNA replication errors become more likely, and this leads to deformed cells and increases the risk of cancer.[18]
Genetic theories of aging
Genetic theories of aging hypothesize that aging is a part of gene composition from the start and that beings are pre-programmed to age. According to this theory, genetic makeup predicts cellular longevity. Programmed cell death, or apoptosis, is determined by a “biological clock” via genetic information in the nucleus of the cell. Cell death on a massive scale would be extremely dangerous for the body, as dead cells would require a lot of resources to be dealt with. Any damage from environmental factors and some mutations to the cell will only increase the pace of an impending and dangerous cellular decline.
Whilst genes responsible for apoptosis explain cell death, however, as there are billions of cells in a human body, this is less applicable to the death of an entire organism. The increasing rate of cellular apoptosis may correlate to aging but it is not a ’cause of death’.
More recently epigenetics and gene expression have been explored as the most significant contributing factor to aging. The epigenetic clock, which relatively objectively measures the biological age of cells, is a useful tool for determining the efficacy of different anti-aging treatments.[19] Horvath’s clock is a stellar example of an epigenetic clock, but newer approaches to determining the pace of aging have been developed since.
General imbalance
General imbalance theories of aging put great importance on to decline of bodily systems such as the endocrine, nervous, and immune systems. Simultaneous decline due to various factors will make the body vulnerable and systems prone to failure leading to further decline. The rate of system failure will vary and will be influenced by outside factors.[20]
Immunological theory
The immunological theory of aging proposes that the reason behind our decline is the weakening immune system. A weaker immune system disables the organism from fighting infections effectively. A compromised immune system will be less able to destroy old and neoplastic cells. Aging will essentially be a one-way road with death as the destination. The immunological theory of aging was developed by Roy Walford in 1969 who stated that incorrect immunological procedures implemented by the body were the ultimate cause[21].
References
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