Fossil hotspots may skew our view of human evolution

When it comes to our understanding of human evolution, we largely depend on fossils. We string together stories of existence, evolution, and extinction from the skeletal remains retrieved from Earth’s crust. However, not all parts of the world offer the same bounty of information.

Africa, often dubbed the cradle of humankind, houses several fossil hotspots. One of the prime examples is the eastern branch of the East African Rift System, known for its abundance of significant fossil sites like Oldupai Gorge in Tanzania.

However, this prolific source of evidence only represents 1% of Africa’s surface area, suggesting we might be missing a substantial part of the evolutionary narrative.

Interpreting early human history

In a new study, experts have investigated the extent to which fossil hotspots like the East African Rift System have biased our understanding of human evolution. The study emphasizes the importance of acknowledging this bias when interpreting early human history.

Study lead author W. Andrew Barr is an assistant professor of anthropology at George Washington University.

“Because the evidence of early human evolution comes from a small range of sites, it’s important to acknowledge that we don’t have a complete picture of what happened across the entire continent,” said Barr.

“If we can point to the ways in which the fossil record is systematically biased and not a perfect representation of everything, then we can adjust our interpretations by taking this into account.”

To understand the extent of this bias, Barr and study co-author Professor Bernard Wood focused on the distribution of modern mammals inhabiting the rift valley.

The researchers found that only a small proportion of medium- and large-bodied mammals were “rift specialists,” and the rift environment encompassed an average of just 1.6% of the total geographic range of modern mammal species.

Bias in human evolution studies

Weighing this finding against the human fossil record, the researchers questioned if we were over-relying on a sample that has a narrow ecological and geographical spread.

This concern was solidified after a second analysis where Barr and Wood compared the skulls of modern primates from the rift valley with those from other parts of the continent. The rift valley skulls represented less than 50% of the total variation among primate skulls in Africa.

“We must avoid falling into the trap of coming up with what looks like a comprehensive reconstruction of the human story, when we know we don’t have all of the relevant evidence,” said Wood.

“Imagine trying to capture the social and economic complexity of Washington D.C. if you only had access to information from one neighborhood. It helps if you can get a sense of how much information is missing.”

Reality beyond the hotspots

While the scientific community has been aware of this limitation, prior studies had not quantified the magnitude of the bias using modern mammals as analogs for human fossils.

Though information from modern mammals doesn’t provide exact locations or environments where our ancestors lived, they can offer crucial indicators to enhance understanding of the environments and physical differences of ancient humans.

Fuller picture of human evolution

The study authors urge the scientific community to broaden their horizons and venture beyond traditional hotspots to uncover new fossil sites.

Barr acknowledged the challenging nature of working outside these traditional hotspots. “There’s a smaller number of people who work outside these traditional hotspots and do the thankless labor of trying to find fossils in these contexts that are really hard to work in, where the geology isn’t favorable for finding fossils,” said Barr.

“It’s worth doing that sort of work to make our picture of mammal and human evolution from this time period more complete.”

Uncovering the mysteries of human evolution is a lot like trying to piece together a jigsaw puzzle with many of the pieces missing.

Recognizing the biases in our existing datasets and refining our approaches can help us get closer to a more complete and accurate picture of our ancestry.

The study is published in the journal Nature Ecology & Evolution.

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