Trying to remember the title, or author of a short story about a tribe of ape-like gatherers who have evolved to live on a seemingly endless vertical wall world, migrating around it in their family groups.
The story follows a youngster who decides to climb upwards against all conventional tribal beliefs.
This was an immense column that took generations to circle, and the climax is the realisation of this by the youngster reaching the top.
The People on the Precipice by Ian Watson.
The story was featured in the Evil Water: And Other Stories collection. Parts of the text are available in the Google eBook version.
The vertical wall is described as follows:
"Just suppose," he said, as the daylight dimmed, "that a whole world is as flat as a leaf! And suppose that creatures live within that leaf, who themselves are perfectly flat. Imagine this narrow ledge here simply carries on" - he chopped his hand into empty space - "in that direction forever! Imagine that it is a simple, infinite surface with nothing above it and nothing below it. And with no precipice to jut out from."
And later, a character's suggestion to climb upwards seems to be a big deal, compared to what's usually done:
"We make daily forays up and down for food. When we've scalped a patch we migrate sideways. That's life."
[...]
"And you'll die clinging on. Or rather, you'll die pretty soon after you stop clinging on. Now, today I'm climbing up to the Chief-of-Chiefs for that conference. Bounce will guard our ledge and keep the kids tied up. Loosepiton" - that's me - "will escort me upwards."
