Global efforts to find the secret to everlasting youth may be futile, as scientists have mathematically proven that it is impossible to halt ageing in multicellular organisms like humans.
Current understanding of the evolution of ageing leaves open the possibility that ageing could be stopped if only science could figure out a way to make selection between organisms perfect.
One way to do that might be to use competition between cells to eliminate poorly functioning "sluggish" cells linked to ageing, while keeping other cells intact.
"Ageing is mathematically inevitable. There's logically, theoretically, mathematically no way out," said Joanna Masel, professor at University of Arizona in the US.
Two things happen to the body on a cellular level as it ages, Nelson said.
One is that cells slow down and start to lose function, like when your hair cells, for example, stop making pigment. The other thing that happens is that some cells crank up their growth rate, which can cause cancer cells to form.
As we get older, we all tend, at some point, to develop cancer cells in the body, even if they are not causing symptoms, researchers said.
They found that even if natural selection were perfect, ageing would still occur, since cancer cells tend to cheat when cells compete.
"As you age, most of your cells are ratcheting down and losing function, and they stop growing, as well," said Paul Nelson from University of Arizona in the US.
"But some of your cells are growing like crazy. What we show is that this forms a double bind - a catch-22," said Nelson, lead author of the study published in the journal
Proceedings of the National Academy of Sciences. "If you get rid of those poorly functioning, sluggish cells, then that allows cancer cells to proliferate, and if you get rid of, or slow down, those cancer cells, then that allows sluggish cells to accumulate," he said.
"So you're stuck between allowing these sluggish cells to accumulate or allowing cancer cells to proliferate, and if you do one you can't do the other. You can't do them both at the same time," he added.
Although human mortality is an undisputed fact of life, the researchers' work presents a mathematical equation that expresses why ageing is an "incontrovertible truth" and "an intrinsic property of being multicellular," Nelson said