On the island of Hirta in Scotland lives a flock of wild sheep. People do not care for them, and the sheep find their own food. Sometimes their numbers swell enormously, and then there is not enough grass for everyone. Scientists spent forty years recording how many sheep survive and how many lambs are born. In this way they hoped to understand whether crowding accelerates aging.
It turned out that it does not. When sheep are numerous, they die more often and reproduce less often, but the rate of aging remains the same. This is like the foundation of a house: wind can tear off the roof, but it will not make the walls crumble faster. Old sheep do not become more fragile in bad years.
This result helps us understand that aging depends mainly on internal processes in the body, not on external hardships. For humans, this means that stress and a shortage of resources can worsen life, but they do not necessarily accelerate biological aging. To measure this precisely, special markers of the body's state are needed, such as epigenetic clocks.
Soay sheep have lived on the island of Hirta without human management for thousands of years, and their numbers fluctuate from 211 to 672 individuals, which makes the population an ideal natural laboratory.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.