Well, the obvious explanation to me is that that did happen, and then the person died of some cause unrelated to these specific signalling molecules. Possibly a

Well, the obvious explanation to me is that that did happen, and then the person died of some cause unrelated to these specific signalling molecules. Possibly another cause of aging. In 1850 the leading cause of death in the US census was "zymotic diseases" and cancer caused death in the triple digits. In 2020, almost none of the diseases in the "zymotic" category are significant in the US, but we're still dying. We've cured croup and scarlet fever, so we don't die of those much any more--instead we live long enough to die of heart disease and cancer. Cancer didn't kill many people in 1850, but that's only because "zymotic diseases" killed them before they could develop cancers.[1] I think it's likely that there are many causes of aging, and they will behave the same way: as we eliminate some causes of aging we'll live long enough to die of other causes of aging that take longer to potentiate. Given most people who reproduce do so before the age of 50, there's not really an evolutionary pressure to not age--in fact, there may actually be evolutionary pressure to age so you die off and leave more resources for more efficient (younger) organisms carrying your DNA. Ghengis Khan, the most evolutionarily successful person in history, died at 64 or 65. So if a person did produce these signaling molecules, they wouldn't necessarily gain any evolutionary benefit from them. [1] Obviously "zymotic diseases" is a nonsense category in modern medicine--most were bacterial infections, some other forms of infections, some completely misattributed to infection. The point here is that most of them weren't cancers or heart disease--the things that kill Americans today.