Why people age so differently remains largely unsolved
Some people reach a hundred in reasonable health. Others decline sharply in their seventies. A new review asks why, and the answer is more complicated than most longevity research suggests.
The review covers what is currently known about the biological mechanisms driving individual variation in lifespan. It surveys genetic variation, epigenetic clocks, immune system function, mitochondrial efficiency, and the rate at which DNA damage accumulates. All of these contribute. None of them fully explains the picture.
One of the review’s central observations is that centenarians, while living longer, are not exempt from aging. They experience the same processes of biological decline as everyone else, just later or more slowly. That makes their biology interesting as a reference point. It does not make them a blueprint for radical life extension.
Heritability explains only part of the variation
The researchers note that heritability accounts for roughly 25 percent of variation in lifespan. The rest comes from environmental factors, molecular stochasticity, and interactions between the two. That stochastic component is significant. Two people with identical genes and lifestyles can still diverge substantially in how quickly their cells age.
Epigenetic variation, changes in how genes are switched on or off without altering the underlying DNA sequence, receives particular attention. This variation increases with age and differs markedly between individuals. It is among the most promising markers for measuring biological age.
The risk of aiming too low
The review closes with a pointed argument. Using centenarians as the target for longevity research sets the bar too low. Centenarians are old and fragile. They live longer, but not necessarily well. The authors argue that the field should aim higher: not to replicate how some people survive longer in decline, but to understand how decline itself can be slowed or prevented.