A recent study highlights how the disparity between fossil locations and the ancient habitats of humans may shape our perception of early human evolution.
The bulk of the early human fossil findings come from a limited number of sites in Africa, where ideal geological conditions have led to the preservation of a wealth of fossils that scientists use to piece together the narrative of human evolution. Notably, one of these rich fossil areas is located in the eastern segment of the East African Rift System, famously known for significant sites like Oldupai Gorge in Tanzania. However, this eastern part of the rift covers only 1% of Africa’s surface area, prompting concerns about the potential gaps in knowledge for researchers who depend on such a narrow sampling.
In a new article released today in the journal Nature Ecology & Evolution, researchers from George Washington University reveal how the clustering of fossil sites in regions like the East African Rift System skews our understanding of human evolution, emphasizing the importance of recognizing this bias when studying early human history.
“Since our understanding of early human evolution derives from a limited set of locations, it’s crucial to recognize that we’re not seeing the full picture of what occurred throughout the continent,” states W. Andrew Barr, an assistant professor of anthropology at GW and the lead author of the study. “By identifying the systematic biases in the fossil record, we can refine our interpretations accordingly.”
To assess the extent of bias in the fossil record, Barr and his collaborator Bernard Wood, a University Professor of Human Origins at GW, examined the distribution of contemporary mammals living in the rift valley. They discovered that there are very few medium- and large-sized mammals that are specifically adapted to the rift environment, which accounts for only about 1.6% of the geographical distribution of modern mammal species.
In a subsequent analysis, Barr and Wood compared the skulls of modern primates from the rift valley to those of similar primates found in other regions of Africa. They found that the skulls from the rift valley constituted less than 50% of the overall variation found in African primate skulls.
While the scientific community has long acknowledged that the rift represents a tiny portion of where ancient humans may have resided, the researchers argue that earlier studies have not leveraged modern mammals as parallels for human fossils to assess the extent of bias. Although modern mammals do not pinpoint the exact locations or environments inhabited by our human ancestors, they serve as valuable hints that enhance our comprehension of the habitats and physical distinctions among ancient humans, as mentioned by the authors.
“It’s crucial to avoid the misconception of constructing a seemingly complete narrative of human evolution when we know we lack comprehensive evidence,” states Wood. “Consider trying to encapsulate the social and economic diversity of Washington D.C. using data from only one neighborhood. Understanding how much information is missing is beneficial.”
The researchers also emphasize the necessity for the scientific community to venture beyond the rift to discover new fossil sites, thereby expanding the geographic breadth of the fossil record.
“There are fewer individuals focused on areas outside these conventional hotspots, diligently searching for fossils in challenging environments where the geology does not favor fossil discovery,” explains Barr, who actively seeks fossils in locations beyond the traditional hotspots. “Engaging in this type of research is essential for creating a more complete narrative of mammal and human evolution from this era.”
