The cliff walls are ecological barriers as profound as any stretch of ocean.

The result, over the millions of years that the tepui summits have existed as isolated highland habitats, is that the organisms living on them have diverged from their lowland relatives through the same processes that operate on oceanic islands.

Species that arrived on the summit — however they arrived, whether by wind, or carried by birds, or by occasional accidental transport — have been evolving in isolation ever since, accumulating the adaptations and the genetic distinctiveness that eventually make them unambiguously new species.

This is why the tepui summits, and Roraima in particular, are such centers of endemism.