The shape of ageing

Time is relative; for a robin a month is almost five per cent of its life whereas for a human it is more like 0.001 per cent of an average lifetime. Ageing is a very different experience for robins compared to humans and in studying the differences between species we might come up with some answers as to what makes ageing happen.

A new research paper has discussed how short-lived species like the robin have a fast pace of ageing whereas long-lived species like humans have a slow pace of ageing. Pace of ageing though is just one dimension of ageing, there is also the shape of ageing to consider.

The shape of ageing refers to how the risk of dying alters with age. For instance birds like the robin and swift have a low ageing factor of around about two. While they may only live one or two years, mortality risk only doubles during its adult life, so age for a robin is not a great predictor of dying. That means the “shape” of ageing for robins is relatively flat.

By contrast, humans have a slow pace of ageing but a steep “shape” of ageing. As a human gets older their risk of dying increases dramatically. For instance, at the age of fifteen a girl has only a two in 100 000 chance of dying but by age 110, one out of every two women will die. So the shape of ageing is steep for humans compared to the shallow ageing curve for the robin.

For this study a range of species were compared. The robin’s adult life is on average only about 1.7 years but their ageing factor is only about two. Humans however, live on average 80 years but have an ageing factor of 2132. So as far as longevity humans win, but as far as the impact of ageing on death risk, the robins are way in front.

The research also included sturgeon, sheep, buffalo, and chimpanzees.

Comparing species may help us understand how evolution has shaped the biology of ageing. This might lead to determining the factors that drive ageing and help us understand how to modify those factors. Maybe one day we can turn the old adage on its head and “live fast, die old” and wouldn’t it be great if we could take some old robins along with us!

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