Humans lived under the leafy canopy of a West African rainforest by at least 150,000 years ago.Previously, the oldest secure evidence for humans living in African rainforests dated to about 18,000 years ago. The earliest human rainforest presence in the world had been placed at about 70,000 years ago in Southeast Asia.Now, new sediment analyses at Bt I, a site in the West African nation of Ivory Coast, indicate that people occupied wet tropical forests tens of thousands of years earlier, researchers report February 26 in Nature. The date and site location may help to explain how Homo sapiens evolved.A researcher holds one of the stone tools found at a site in the African nation of Ivory Coast that helped to uncover the oldest known human rainforest occupation.Jimbob Blinkhorn, MPGBt I was discovered in the early 1980s. Stone artifacts unearthed there from 1982 to 1993 include large implements suited for cutting fibrous plants and other tropical forest resources. In 2020, archaeologist and geochronologist Ben Arous and colleagues, including one of the sites original excavators, Francois Yod Gud, relocated the site.Their new investigation completed shortly before quarrying destroyed Bt I used two sediment dating methods to obtain an age estimate for the sites stone tools. Sediment samples contained pollen, plant remains and chemical remnants of plants waxy coating typical of humid, West African rainforests today. Dense woods resulted in low levels of grass pollen at the ancient site, the researchers report.Ancient rainforest pioneers served as ancestors of later Stone Age populations in Ivory Coasts rainforests and in coastal mangrove forests farther north in whats now Senegal, suspects Eleanor Scerri, Arous colleague at the Max Planck Institute of Geoanthropology in Jena, Germany.The new findings also strengthen an argument that H. sapiens evolved roughly 300,000 years ago via mating among populations based in different African regions and habitats, including West Africas rainforests. Even around 150,000 years ago, when these groups coalesced, their exchanges shaped the course of our evolution and likely contributed to the success of our species, Scerri says.