There are several evolutionary theories of aging that attempt to explain why aging occurs from a biological and evolutionary perspective. These theories generally suggest that aging is not directly selected for, but results from the way natural selection operates over time. The major theories include:
1. Mutation Accumulation Theory (Medawar, 1952)
• Core idea: Harmful mutations that affect individuals later in life accumulate in the gene pool because natural selection is weaker at older ages.
• Reasoning: Since most organisms die from external causes (e.g. predation, disease) before reaching old age in the wild, natural selection does not strongly act against genes that cause late-onset diseases.
• Result: Aging is due to the buildup of deleterious late-acting mutations.
2. Antagonistic Pleiotropy Theory (Williams, 1957)
• Core idea: Some genes have pleiotropic effects, meaning they influence multiple traits—beneficial early in life but harmful later.
• Example: A gene that boosts fertility or physical strength early in life might cause tissue damage or cancer later on.
• Result: These genes are favored by natural selection despite their negative effects in old age because they increase reproductive success.
3. Disposable Soma Theory (Kirkwood, 1977)
• Core idea: Organisms have limited resources, which must be allocated between reproduction and body maintenance (soma).
• Trade-off: Investing heavily in reproduction may come at the cost of maintenance and repair of the body, leading to aging.
• Result: Aging is the price paid for maximizing reproductive success with finite resources.
4. Programmed Aging Theories (less widely accepted)
• Core idea: Aging is a genetically programmed process, controlled by biological clocks and regulated pathways.
• Examples: Some believe aging may have evolved to remove older individuals to free up resources for the younger generation.
• Criticism: Many evolutionary biologists argue that evolution does not favor traits that limit individual survival unless there is a group-level benefit, which is controversial.
5. Evolutionary Senescence Theory
• This is a broader concept that encompasses the above ideas. It suggests aging is a byproduct of natural selection’s focus on reproductive fitness, not longevity.
Summary Table
Theory
Key Mechanism
Implication
Mutation Accumulation
Weak selection on late-acting genes
Aging = accumulated damage
Antagonistic Pleiotropy
Genes beneficial early, harmful late
Aging = genetic trade-off
Disposable Soma
Trade-off: reproduction vs. maintenance
Aging = underinvestment in repair
Programmed Aging
Aging is genetically regulated
Aging = evolved lifespan control (controversial)
Written by Professor Dr. Aqeel Al Jothery (PhD UK).
Anesthesia Techniques Department, College of Health and Medical Technologies, Al-Mustaqbal University
Al-Mustaqbal University is the first university in Iraq