Researchers found that focus on fossil hotspots in Africa where most human fossils are found creates bias in our understanding of early human activity across the continent in a study published Tuesday. 

The study — led by W. Andrew Barr, a GW assistant professor of anthropology and co-authored by Bernard Wood, a University professor of human origins — found that sites in areas like the East African Rift System, where researchers excavate many human fossils, make up on average only 1.6 percent of the total geographic range of modern mammal species. Wood said the study aimed to convince researchers that information collected from existing hominin and hominid fossil sites may be comprehensive for those sites but is not representative of the complete possible fossil record across Africa. 

“We’re trying to persuade people not to fall into the trap of thinking that’s because that’s where the fossils came from, that’s where they lived, and that’s where they like to live,” Wood said.

Wood said researchers wanted to understand the amount of information absent from the fossil record because of the abundance of research sites in the East African Rift System — a continental rift valley where two tectonic plates meet — and in south African cave systems. Wood said since paleontologists seek to reconstruct evolutionary history through the discovery of fossils, evidence is usually collected at a less frequent level than in experimental sciences.

“We don’t know where the hominins lived in Africa, they could have lived all over Africa, they could have lived in certain parts of Africa where the climate and habitat were suitable,” Wood said. “But we only know where they were because of the fossil sites and the reasons that the fossil sites are there are nothing to do with whether those early hominins liked those places, they just happen to be places where we find evidence.”

Wood added that research is often concentrated in this geographic area because erosion in the region has exposed layers of sediment containing fossils within the rift valley, eliminating the labor and time costs researchers would have if they were studying fossils elsewhere.

Wood said researchers used existing data sets on living animal species like baboons and monkeys to compare information like habitat preferences and skull shape. He said researchers compared data sets from the East African Rift System with data collected across Africa to gauge how representative the system is of species diversity across the entire continent.

“Some of these data sets have taken a decade to accumulate, so we just sort of hitchhiked on those data sets,” Wood said.

Wood said researchers don’t know how much of the fossil record they would need to recover to get a “reasonably good” idea of the process of human evolution, but they can estimate the constraints from overrepresentation of research at specific site areas. 

“It’s comprehensive for what we have, but it’s not comprehensive for the problem that we’re trying to solve, so I think that’s the message, really,” Wood said.

Experts in human evolution said the study reveals the tendency of researchers to generalize their understanding of human history based on a small sample of fossil findings. 

Michael Bisson, a former professor of anthropology at McGill University, said the reason researchers find more fossils in such a small area of Africa is because those are often locations full of volcanic ash, changing the composition of the soil to make it more suitable to preserve fossils.

“We will never be able to assess the fossil record in lots of parts of Africa simply because the fossil record doesn’t exist,” Bisson said. “But the fact that fossil record doesn’t exist doesn’t mean that hominins weren’t there.”

Bridget Alex, a lecturer in human evolutionary biology at Harvard University, said the solutions that the study provides to fill in gaps in research, like looking at biological variations in live mammals to estimate what their ancestors would look like in different habitats, provides a useful way to address limitations to the fossil record.

“It doesn’t just point out that there’s a problem, which kind of everyone knew, it offers a pathway for being able to estimate how problematic are your results whenever you find a fossil and you’re trying to generalize about all human ancestors and relatives who lived to, say, four million years ago, because you found a fossil at one particular site,” Alex said. 

Craig Stanford, a professor of biological sciences and anthropology at the University of Southern California, said researchers might not be eager to diversify their searches throughout all of Africa because they want to go to places where they know they are more likely to find a fossil. 

“It’s the scientific discovery and also the personal ambition side that has led everybody to be drawn to where the discoveries have already been made,” Stanford said.