To understand why Roraima’s summit hosts so many species found nowhere else, it helps to understand what biologists call “island biogeography” — the study of how isolation affects the diversity and evolution of life on islands.

The classic context for island biogeography is oceanic islands — pieces of land surrounded by water, accessible to colonizing species only by crossing a marine barrier.

Islands receive colonists from the mainland sporadically and infrequently, and the colonizing species that establish populations on an island do so in the absence of many of the competitors and predators that constrained them on the mainland.

Over time, island populations diverge from their mainland ancestors as natural selection acts on them under island conditions — and as they accumulate random genetic changes through the process called genetic drift.