Humans don't replenish all of our cells. That's why we have memories stored in our brains. The proteins in our eyes doesn't replenish which is our eyes go bad with age.... And on and on.
I don't know what there is about the hydra that applies to humans. An interesting animal, but ultimately too alien to what humans are. If biological immortality rests on replacing every cell with age, then what is life and consciousness? Since everything in the body is ultimately recycled then are we not already immortal?
Neurons have lasted over 50% longer than the average lifespan of humans, in other animals upon transplant they've lasted twice as long as the original host. Some have suspected, and suggested, they exhibit negligible senescence and it is the aging of support cells that causes their degeneration
In some organisms, physiological reversal of things like lipofuscin accumulation has occurred, iirc.
6.5.8 Reversal of Lipofuscin Accumulation Lipofuscin accumulation
-The Future of Aging: Pathways to Human Life Extension
Again decades of additional lifespan(over average) proven in human without genetic modification, double lifespan of host proven in other species.
The brain depends on the molecular garbage export system known as the glymphatic system to function, without it it is like a city without the garbage trucks.
Here's an article showing that loss of brain performance, function and structure is significantly slowed in a fraction of the population
http://www.nextbigfu...g-minds-as.html
Edited by Castiel, 20 September 2016 - 08:10 PM.