Challenging the Out of Africa Theory: Evidence of Early Human Habitation in West African Rainforest

For decades, the prevailing scientific understanding of human origins has centered around the "Out of Africa" theory. This model posits that early humans initially thrived in the open grasslands of East Africa, subsequently dispersing and adapting to various environments across the globe. However, a groundbreaking new study is challenging this long-held belief, presenting compelling evidence that our ancestors successfully inhabited a tropical rainforest in West Africa much earlier than previously thought.

The study, published this week in the prestigious journal Nature, unveils findings from a research team that unearthed signs of human presence in what is now southern Côte d’Ivoire, a region characterized by dense rainforest. The evidence suggests that humans resided in this area approximately 150,000 years ago, a time when rainforests were generally considered insurmountable barriers to human habitation.

According to Eslem Ben Arous, an archaeologist from Spain’s National Centre for Human Evolution Research and a key author of the study, the discovery significantly pushes back the timeline of human presence in rainforest environments. "Before our study, the oldest secure evidence for habitation in African rainforests was around 18,000 years ago, and the oldest evidence of rainforest habitation anywhere came from southeast Asia at about 70,000 years ago," Ben Arous stated. "This pushes back the oldest known evidence of humans in rainforests by more than double the previously known estimate."

The implications of this finding are profound. It suggests that early humans were more adaptable and resilient than previously assumed, capable of thriving in diverse ecosystems beyond the open savannas traditionally associated with human origins.

Eleanor Scerri, the leader of the Human Palaeosystems research group at the Max Planck Institute of Geoanthropology and a co-author of the new study, highlighted the limited knowledge we currently possess about the complex history of the African continent. "Though it’s widely believed that humans first originated about 300,000 years ago from one part of Africa, we understand very little about the continent’s history," Scerri explained.

The investigation into the possibility of early human habitation in West African rainforests stemmed from the emergence of evidence indicating similar habitation patterns in Asian rainforests. Scerri and her team sought to explore whether the same phenomenon might have occurred in West Africa.

However, uncovering evidence in this region presented significant challenges. Scerri emphasized the notoriously poor preservation of ancient botanical materials in rainforest environments. Additionally, the unpredictable rainfall patterns in African rainforests raised the possibility that these areas may not have consistently been rainforests throughout history.

Despite these hurdles, Scerri persevered. Her research led her to an obscure, decades-old book written in Russian that described a deeply buried archaeological site located next to a river in Côte d’Ivoire. Further climate research suggested that the area may have served as a rainforest refuge in the past.

The site was initially uncovered in 1982 during a joint Ivorian-Soviet expedition led by archaeologist Professor Yodé Guédé of the Université Félix Houphouët-Boigny. However, the team at the time lacked the advanced tools and techniques necessary to accurately determine the age of the stone tools they discovered or to reconstruct the environmental conditions that prevailed when humans inhabited the site.

Scerri acknowledged the high quality of the original research but lamented its limited impact. "The research was strong, but because it was published in Russian and because it was West Africa, no one was interested, and no one knew about it," she stated.

Undeterred, Scerri and her colleagues embarked on a mission to track down Professor Guédé, now in his 80s. With his guidance, they returned to the vast trench where the initial discoveries had been made. Fortuitously, the team managed to clear vegetation and collect crucial samples in March 2020 before being forced to evacuate the country due to the COVID-19 pandemic. They were able to return briefly before the site was ultimately destroyed by quarrying activities.

Scerri expressed immense satisfaction in witnessing Professor Guédé’s joy at seeing his decades-old research project finally come to fruition. "One of the most rewarding things was just to see the happiness on Professor Guédé’s face that this project that goes back to the 1980s, he was finally able to close that chapter," she said.

Over the subsequent years, Ben Arous spearheaded the development of novel techniques for dating quartz grains extracted from the oldest layer of sediment where the stone tools were found. A separate laboratory independently verified the results using a different dating method known as luminescent dating.

"It’s around 150, 160,000 years old, which was exciting because it’s like one of only two sites in West Africa that are that old," Scerri exclaimed.

The team then meticulously analyzed isotopes from the waxy coating of leaves, which Scerri described as "surprisingly indestructible," as well as solidified plant remains and ancient pollen samples. The evidence revealed that the site was not merely a small forested area but a densely wooded environment characterized by the presence of key rainforest tree species, such as oil palms and hunteria.

Scerri emphasized that the team is continuing to analyze sediment samples and stone tools collected from a nearby site. She also called for increased exploration of West Africa to gain a more comprehensive understanding of these artifacts.

The findings of the study have far-reaching implications, challenging the traditional narrative that humans gradually learned to adapt to different ecosystems as they evolved. "It reinforces the idea that humans have multiple roots across Africa, and that from our inception almost we were a species that could and did survive in very, very different ecosystems," Scerri asserted.

She concluded by drawing a parallel between the adaptability that enabled early humans to thrive in diverse environments and the ingenuity that has propelled humanity to achieve remarkable feats, such as space exploration. "And the same skills that allowed us to do that, are the same skills that have put us on the moon and have us looking forward to going to Mars. It’s human adaptability and our ingeniousness, coming up with ways in which you can adapt to radically different environments, is unknown in any other animal."

This groundbreaking study underscores the importance of reevaluating long-held assumptions about human origins and the need for further research to unravel the complex and multifaceted history of our species. It also shines a light on the often-overlooked contributions of scientists from underrepresented regions, whose work can hold invaluable clues to understanding our past. The evidence from Côte d’Ivoire adds a significant chapter to the ongoing story of human evolution, reminding us that our journey is far more intricate and geographically diverse than previously imagined.