"More than half of the world's species of plants and animals are found in the rainforest."

Allan Krill

"The great diversity in rainforest species is in large part the result of diverse and numerous physical refuges, i.e. places in which plants are inaccessible to many herbivores or in which animals can hide from predators." (Wikipedia)

Chimpanzees, gorillas, and orangutans live in rainforest. Could humans have speciated in African rainforest? There are no fossils there, so paleoanthropologists avoid that question. Paleoanthropologists focus on drier places — no apes, but lots of fossils.