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A cure for aging? Not yet.

"Clearance of p16Ink4a -positive senescent cells delays ageing-associated disorders" is an accurate statement of the results presented in a recent paper in Nature. I guess the title would have been too long if they'd added "...in mice genetically engineered to have short-life spans, but the treated mice didn't live longer."

The authors argue that "removal of senescent cells can prevent or delay tissue dysfunction and extend healthspan." They hypothesize that senescent cells release chemicals that cause excessive aging of other cells nearby. So they genetically engineered mice, which were already genetically engineered to age faster than normal, so that their senescent cells could be killed by a drug. Giving the mice the drug eliminated senescing cells faster and had various health benefits, such as better performance on treadmills, relative to the same fast-aging mice not given the drug.

But our ancestors already evolved mechanisms, long ago, to eliminate cells that are no longer needed or are causing problems, like cancer. Are those evolved mechanisms too slow? If so, why? That is, why haven't mutants that clear these cells faster out-competed those that clear them slower? Speeding up an existing natural process is well within the capabilities of natural selection.

Sometimes, there can be trade-offs between longevity (or late-life vigor) and reproduction, especially early reproduction. In such cases, natural selection will often -- but not always -- favor early reproduction over longevity. Could keeping senescing cells around longer increase fertility, or something? If so, then a drug that would speed the elimination of senescing cells could still be useful. We just wouldn't take it until we were finished having children.

But speeding the clearance of senescent cells in older but not younger individuals doesn't seem too difficult for natural selection to have managed either, given millions of years to work on the problem. I'm assuming that older individuals have been contributing to the survival of their children and grandchildren for at least a few million years.

I'm betting that faster-than-natural clearance of senescent cells, which didn't extend actual life-span even in mice engineered to age faster than normal, won't do much for the health-span of normal mice.

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