On day 21 of adult life, three quarters of the worms are already dead, and the survivors barely twitch. It was at that very moment that the scientists intervened and gave them another 26 days, even though the control individuals lived only four. Aging turned out to be not an accumulation of breakdowns but a descent down an unstable slope: you don't have to remove the stones, you just have to make the gradient gentler.

The experiment was built on the nematode C. elegans, in which the insulin receptor DAF-2 was tagged with a special label. When auxin was added, the protein was destroyed within 30 minutes, and after the substance was removed, it was restored. This way the signaling pathway could be switched off and on at any age, like a toggle switch. In 21-day-old worms, the intervention halted the breakdown of the outer cuticle, restored resistance to heat and salt stress, and partially dissolved protein clumps, although age-related diseases of the pharynx, gonads, and uterus did not go away.

To understand why late intervention works just as well as early intervention, the scientists built a mathematical model. The state of the organism was described by a single variable that changes under the influence of random noise. Death occurs when this variable reaches a critical threshold for the first time. The model reproduced the experimental survival curves if the intervention lowered the instability parameter without changing the noise level and without resetting the accumulated state.

A worm on the threshold of death received a second life not because it was repaired, but because the rules of its fall were changed. The slope became gentler, and the stones that used to knock it off its feet now simply lie in its path.

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