The earliest evidence of humans living in tropical wet forests has been pushed back approximately 70,000 years, thanks to research from a group of scholars, including Bryant’s Robert Patalano, Ph.D. 

The study’s scientists re-dated and reconstructed the ancient environments at the Bété I archaeological site of Anyama, Côte d'Ivoire in western Africa. Anyama was first excavated by Russian-Ivorian archaeologists in the 1980s and ’90s but most of the artifacts were destroyed during the 2010 civil war. The site was revisited by a research team led by the Max Planck Institute of Geoanthropology in 2020, and samples were collected for dating and paleoenvironmental analyses.

With findings recently published in Nature and highlighted in The New York Times, Patalano — who teaches in the School of Health and Behavioral Sciences’ Biological and Biomedical department — talks about his involvement in the study: 

For this study, you conducted environmental reconstructions for the site. What did that process entail? 

I analyzed plant wax biomarkers from the site. Plant waxes are a class of chemical compounds found on the outer surface of plants, mainly on their leaves. These compounds help protect the plant from harmful UV radiation, insect and fungal attack, water loss, and other effects that could hurt it. Different plants produce different types of waxes; for example, wetland and aquatic plants produce certain biomarkers that are distinct from plants that grow on land. By looking at the ratio or total amount of biomarkers produced by wetland plants versus those produced by land plants, you can get a sense of the types of environments these plants lived in — and in this case, the humans living at the site. 

Biomarkers are recovered from archaeological sediments. Typically, we extract them from sediments using organic solvents using the “like dissolves like” principle; that is, the organic solvents have similar properties to biomarkers, and because of that, the solvents bind with the biomarkers and pull them from the sediment. From there, we separate the biomarkers into specific types, again using organic solvents. The two biomarkers we targeted in this study were normal (n-) alkanes and fatty acids (n-alkanoic acids). We can calculate the relative abundance of these compounds using gas chromatography and mass spectrometry and then determine which were produced by wetland, aquatic, or land plants. This information was then compared to the phytolith and pollen data from the site, because one proxy on their own cannot show the full picture of what the environment was like in the past. 

This study pushes humans’ occupation of tropical forests back by approximately 70,000 years. What impact does this new information have on the science and history fields? 

Up until recently, tropical forests were always thought to be “barriers to human evolution” in that humans were not known to survive in these environments because food resources were hard to acquire. A few recent studies based in Kenya and Sri Lanka, however, showed that this wasn’t necessarily the case, and found that people had been living in tropical forests about 80,000 years ago and created sophisticated bone and stone tools to acquire forest resources. 

Anyama is interesting in that not only is it a tropical forest, but it is also a wet tropical forest. Because we don’t have a rainfall proxy, we cannot say the site was specifically a rainforest when people were living there 150,000 years ago, but our biomarker, pollen, and phytolith data all suggest that the area had ecological elements of rainforests, riparian forests, and swamp forests. This information means humans adapted to these types of environments much earlier in our evolutionary history than previously thought and shows that our species has been incredibly adaptable to a range of biomes; this characteristic is likely why we’ve been so successful as a species.

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What other interesting or surprising findings did you and fellow researchers uncover? 

Most human evolutionary research has been conducted in eastern and southern Africa because the tropical forests of west and central Africa have always been seen as barriers to human habitation. Tropical forests are hard to navigate even today, and the density of plants makes it challenging to locate archaeological sites. Also, bones do not tend to fossilize in forest environments because the soils are usually too acidic and break down bones before they can fossilize. However, this is not an issue for stone tools. This research shows that we need to invest time and resources into exploring tropical forests for additional archaeological sites; these habitats could provide valuable insight into our evolution and the environmental factors that influenced the biological and cultural evolution of early populations of Homo sapiens and our evolutionary ancestors. 

What additional research questions has this research prompted? 

This study certainly opens the door for more research questions: How far back in time did humans first start living in wet tropical forest environments? Was this an adaptation that only Homo sapiens developed, or did earlier species like Homo erectus or Homo heidelbergensis also have the ability to live in tropical forests? Was the site a rainforest? Where else might we find archaeological sites in tropical forest regions?  

I had several Bryant students help with sample preparation when doing this study. If any students are interested in human evolution or environmental reconstruction, I’m always happy to train them in various laboratory procedures and work alongside them in the lab. Unfortunately, the Anyama area was destroyed by mining and the sites can no longer be accessed. There still are, however, a lot of collected archaeological and environmental samples that are stored and can be studied.