Theories for biological aging

Survival Circuit

In Lifespans, Sinclair outlines popular theories behind aging1:

Selfish gene theory: Natural selection causes us to build a strong and healthy body during the fertile years (18-40), but declines rapidly after the point where we have likely passed along our genes. Proposed by J. B. S. Haldane, Peter B. Medawar, and George C. Williams. Medwar called this antagonistic pleiotropy, genes that help us do not help us when we age, they may actually be detrimental. Natural selection does not advantage an organism that has already passed along its genes. Disposable Soma Hypothesis: Thomas Kirkwood argued that the organisms evolve to breed fast and die you or breed slowly and maintain your soma (body). The idea being that you cannot do both due to energy. Any organism that did both would exhaust resources and delete itself from the gene pool. Loss of genetic information: Peter Medwar and Leo Szilard argued that againg is caused by genetic information being lost to DNA damage. Error Catastrophe Hypothesis: Mutations in the DNA replication machinery reproduce infinitely until a persons genome has been copied into oblivion. Argued by Leslie Orgel in 1963. Free Radical Theory of Aging: unpaired electrons whiz around cells damaging DNA through oxidation, particularly in mitochondria. Proposed by Denham Harman.

  • This theory is popular and persistent, but Sinclair argues that it has not been borne out. The positive health effects of antioxidant-rich diets are more likely because they boost the body’s natural defenses against aging, including enzymes that eliminate free radicals.
  • Cloning refutes the idea of DNA damage causing aging. Clones would be born old if DNA damage was the cause of aging since they are replicating the DNA state. This is not the case, clones live a normal life.


PhD, D. A. S. & LaPlante, M. D. Lifespan: Why We Age and Why We Don’t Have To. (Atria Books, New York, 2019).