Research directions
Paradoxes of ageing
If you see paradoxes in a theory, you are probably on the right track. They reveal where a familiar explanation stops working and a new question begins.
Three clues to how ageing works
An organism grows old, yet its offspring starts young. A mammal lives for decades without the usual rise in mortality. A huge body keeps cancer in check better than a simple calculation predicts. Each observation makes us examine an assumption that once seemed obvious.
A young life from cells with a past
Every newborn is the latest link in an ancient chain of cells. Somewhere along that chain, youth starts again.
What we would expect
Eggs and sperm come from living cell lineages with a history of their own. If age-related damage simply accumulated and passed unchanged from one generation to the next, each new generation would start with a heavier burden.
What researchers found
In 2021, Kerepesi and colleagues analysed chemical marks on DNA during mouse development. Several epigenetic clocks, tools that estimate age from these marks, showed a fall in estimated age early in embryonic development, followed by a rise. The youngest point most often fell around days 6.5–7.5 after fertilisation.
Where the paradox leads
This suggests that early development includes a natural rejuvenation process. The measurement concerns epigenetic age; the removal of every kind of damage remains a separate question. The opportunity is to identify which parts of that process might help an adult tissue recover while keeping its specialised function.
A mammal with a different mortality curve
Imagine that another birthday barely changes your chance of surviving the coming year. Naked mole-rats bring that scenario into the laboratory.
What we would expect
In humans and many other mammals, adult mortality risk rises with age. A body that steadily loses its ability to cope with damage should become increasingly vulnerable.
What researchers found
In 2018, Ruby and colleagues analysed records from more than 3,000 captive naked mole-rats. Across the observed age range, the risk of death showed no detectable increase with age. These mouse-sized rodents can live for more than 30 years.
Where the paradox leads
The striking feature is the shape of the mortality curve. A theory of ageing must account for a mammal that maintains such resilience for decades. The animals still die, and individual tissues may change with age; observations at the oldest ages are limited. The research target is the machinery that keeps those changes from producing the usual rise in mortality.
A giant body and the cancer arithmetic
An elephant has far more cells than a mouse. Each cell is another place where a tumour might begin. A simple calculation makes being an elephant look like a terrible idea.
What we would expect
If cells in different species had the same chance of becoming cancerous, more cells and more years of life would bring a much larger cancer risk. That expectation lies behind Peto’s paradox.
What researchers found
A 2022 study of 191 mammal species found that cancer mortality was largely independent of body size and adult life expectancy. But a 2025 analysis of 263 vertebrate species found more malignant tumours in larger species. The studies measured different outcomes: cancer-related death and tumour prevalence at necropsy.
Where the paradox leads
The question becomes sharper as the evidence grows: how much protection evolves alongside a larger body? The 2025 analysis linked rapid body-size evolution in mammals and birds to lower tumour prevalence. Peto’s paradox directs attention to the evolution of cancer defences and to how we measure their success.
A good paradox leads to an experiment
The most useful contradiction gives us something to test. Find what makes embryonic cells younger. Identify what keeps mortality low in a long-lived mammal. Discover which defences let large bodies resist cancer. A theory gains strength when it can explain the exception and predict what happens next.
Explore experimentsThe wider strategy
The presentation separates theories from lists of age-related changes. Paradoxes supply demanding observations against which those theories can be compared.
The Death-Fighting Spectrum presentation