When the people of old sought unending lives, they'd neglected the aftermath. Those who'd attained the so-called holy grail of humanity knew better and that was why there were so few of them. Few foolish people before what they'd done sunk in, before they realised they'd only scripted themselves to be the food-source of the surviving human race - because they were no longer human: their bodies repaired infinitely and did not age inside, but their minds quickly began to show signs of rot. The man who'd been the first to discover the secret that had eluded them for almost three millennia was the first to give in to catatonia, and the one to show those he'd sired what they had to pay. Because it was a time of drought and famine and despair, and a hungry child had crawled on to his lap and bit into his arm when he failed to respond.
And so the humans were saved from the famine, because the flesh healed after a little, and the blood that spilt in the meantime quenched their thirsts. It was abhorrent for most except the most desperate at first, but the drought persisted. And the immortals had given up themselves by then: they were shells, inexhaustible sources of food and fluid to nourish them. They had a source of survival again, and effort could drift away from that basic need and towards furnishing the world again. And the immortals remained shells, occasionally but never again intelligently moving and making sounds, alternating between being devoured and remade in a cycle the mortal amongst them thought would go on for eternity.
But when the raw desire for survival was pushed to the back of their minds, it transformed. Generations passed. Earth was rebuilt into its former glorious kingdom and the immortals were forgotten for what they were, what they'd once been. They were foodstock and drinking fountains and nothing more, and so people forgot the price they'd paid for their eternal life and began seeking the fruit of that tree once again.
They neglected the truth that sat in front of them, the truth that stirred in their bellies, the truth that was the consequences of what they sought. It took a few people to accomplish it and have their bodies outstrip their minds before the lesson sunk in anew. And other trees dropped the rotten fruit husks of other endeavours, other lessons the past had already granted once but had been forgotten. So the world was caught in an eternal sphere, made up of smaller loops around an axis that was the planet surviving the ages, surviving the humans walking upon it, waxing and waning, living and dying and changing into something no longer human and learning and forgetting, and never realising they were not advancing or regressing but rather repeating a cycle that didn't change at all.
The Writing Challenge Contest at the Review Game, December 2015
More of a concept spiel than a story. Not the same brand of immortality as in my WIP novel though.