In South Asia, there is now compelling archaeological evidence that Homo sapiens rapidly adapted to life in rainforests. At Niah Cave in Borneo, toxic plants obtained from nearby rainforest habitats were being processed as far back as 45000 years ago, soon after people were first documented in this region.
If early humans could adapt to the rainforests of South Asia, then perhaps they also did so much earlier in Africa at the inception of our species. We now know that our species first arose in Africa more than 300000 years ago, leaving plenty of time for our ancestors to adapt to varied habitats.
But finding conclusive evidence for rainforest habitation is difficult. Rainforests are very challenging fieldwork environments, not least because the warm and wet conditions mean that very little of the archaeological record survives the test of time.
In addition, Africa's rainforest ecologies are fragile, sustained by annual levels of rainfall that are at the lowest limit of what is required to maintain a rainforest. This means that there were frequent episodes of rainforest fragmentation in prehistory, making it difficult to establish the environmental context of past human habitation in regions that are forested today.
An ancient hominin tooth from Central Africa indicates that our hominin ancestors were already living in mixed environments at the edges of forests around 2.5 million years ago. Composite foraging tools argued to be forest-adapted may have appeared as early as 265000 years ago and have been found across vast regions of modern rainforest. And new evidence published this year shows that humans were exploiting mixed tropical forest/grassland environments in Kenya up to 78000 years ago.
Later human fossils dating to around 22000 years ago from the Democratic Republic of Congo and 12000 years ago in southern Nigeria feature enough distinctive morphological features to suggest that the populations they belonged to did not often mix with others from elsewhere in Africa. Specifically, these fossils bear more physical similarities to people living between 100000 and 300 000 years ago than their contemporaries. It's possible that they were separated because they had adapted to life in very different environments.
My fieldwork in tropical West Africa has also uncovered striking cultural similarities. Some groups living here up to 12000 years ago were making stone tools that were more typical of people living in similarly earlier time periods. This is not akin to findings from elsewhere which emphasise the late presence of a single artefact form in an otherwise “advanced” tool kit. My findings from Senegal could easily be transplanted to a situation 50000 or 100000 years earlier, and they would not look out of place.
It seems that our species shared Africa with other, more genetically divergent hominins such as Homo heidelbergensis, Homo naledi and perhaps other as yet undiscovered species.
Given the extraordinary discoveries of the last decade, it is certainly wise to keep an open mind and shy away from overly dogmatic assertions about human evolution. The only inescapable fact is that there is a lot yet to be discovered.
Scerri writes for The Conversation at Wits University. She is a visiting Research Fellow from Oxford University.