Why Aging Isn’t Inevitable

The great variety of aging styles among plants and animals suggests it can be controlled

Illustration: Nora Krug

By Josh Mitteldorf and Dorion Sagan

Humans age gradually, but some animals do all their aging in a rush at the end of life, while others don’t age at all, and a few can even age backward. The variety of aging patterns in nature should be a caution sign to anyone inclined to generalize — particularly the generalization that aging is inevitable.

Bacteria reproduce symmetrically, just dividing in two. What could “aging” mean for bacteria since, after reproduction, there is no distinction between parent and child? Single-cell protists like the amoeba also reproduce symmetrically, but curiously, they invented a way to age nevertheless. And even among macroscopic life forms, life spans of organisms are immensely variable in a way that is finely tuned to local ecologies and reproduction rates. This can hardly be the result of a universal, inexorable process; in fact, such fine-tuning to circumstance is the signature of an adaptation.

SUDDEN DEATH: Mayflies, like this one, tend to die rapidly and suddenly at the end of their reproductive cycle. Photo: Mick Talbot/Flickr/CC BY 2.0

Life spans range from Methuselans great and small to genetic kamikazes that die of a…