Why the Neanderthal vanished earlier than we thought

Nearly two centuries after Dutch naturalist Philippe-Charles Schmerling discovered the first Neanderthal fossil in 1829, we’re still trying to piece together the puzzle of our ancient kin.

One of the most hotly-debated topics in the field of ancient history is the disappearance of the Neanderthals. Exactly when these ancient humans went extinct is contested.

But a study published Monday in the journal Proceedings of the National Academy of Sciences offers new answers — and updates the timeline of when Neanderthals may have vanished from Europe.

When did Neanderthals go extinct?

A team of researchers from Belgium, England, and Germany collaborated across disciplines and arrived at a surprising hypothesis: Previous scientists had gotten the timeline for Neanderthal extinction wrong.

The scientists found that Neanderthals had likely disappeared from northwestern Europe roughly 40,000 to 44,000 years ago — earlier than previously thought.

Previous radiocarbon dating analysis of Neanderthal remains found in what’s known as the Spy Cave in Belgium determined ages as recently as 24,000 years ago. Meanwhile, it’s more commonly accepted Neanderthals disappeared some time between 30,000 and 40,000 years ago.

This study’s team conducted a new analysis on the Spy Cave Neanderthals, as well as other Neanderthal remains found in Belgium, finding a new disappearance time frame.

Necessary background — Extinction, when it comes to Neanderthals, is complicated. While no Neanderthals live today, some scientists don’t view their disappearance as “true extinction” because they were assimilated into the modern human gene pool.

Meanwhile, previous research indicates Neanderthal’s use of stone tools likely ended sometime between 39,000 to 41,000 years ago — suggesting an end of life.

It’s also very likely Neanderthal disappearance happened in waves. Some research suggests there were late-surviving or “transitional” Neanderthals.

This team wanted to better assess the timeline of Neanderthals’ disappearance from Europe using fossils found in caves in Belgium. To date, archaeologists have discovered Neanderthal remains in nine caves in Belgium.

One particular site, the Spy Cave, has intrigued researchers for the sheer number of Neanderthal remains that it contains. Original excavations conducted in the late 1800s discovered 89 hominin bone fragments of two different Neanderthal individuals, while subsequent investigations have discovered 24 more Neanderthal fossils.

How they did it — The researchers developed a more robust method for dating Neanderthal specimens using “compound-specific radiocarbon analysis.”

This method isolates a single amino acid — amino acid hydroxyproline (HYP) — from bone collagen. It’s more robust compared to other radiocarbon dating methods because the amino acid is found only in the collagen of mammals.

Using this compound-specific technique, researchers retested four Neanderthal specimens in the Spy Cave, coming up with new dates for each one. They also used this method on Neanderthals found in Engis and Fonds-de-Forêt.

Based on these dates, the scientists constructed a statistical model to determine the likelihood of the latest Neanderthal occupation of Belgium.

Digging into the details — The researchers found that the Neanderthal specimens were older than previously thought — some up to 10,000 years older.

Their statistical model stated there was a very strong probability, 95 percent, that Neanderthals became extinct in northwestern Europe roughly 40,600 to 44,200 years ago.

The study team writes:

“When redating Paleolithic sites using this so-called ‘compound-specific radiocarbon analysis’ (CSRA) approach, we have observed that many of the previous radiocarbon dates obtained after less robust pretreatments are inaccurate. This can in turn lead to erroneous interpretations of human and faunal dispersal and rates of change in the archaeological, climatic, and evolutionary record.”

The researchers suggest the fossil preservation techniques used in the 1800s, which involved applying glue made from animal collagen, could have made it more difficult for subsequent scientists to accurately date these Neanderthal specimens — and lead to inaccurate dates.

But using their new method, the scientists in this study were effectively able to “decontaminate” the fossils, allowing for accurate analysis.

Why it matters — Getting the date of these Neanderthal fossils precisely right is crucial to understanding the extinction of Neanderthals, as well as their relationship to the first modern humans.

“Dating is crucial in archaeology,” co-author Tom Higham, a University of Oxford professor and director of the PalaeoChron research project, explained in a statement.

“Without a reliable framework of chronology we can’t really be confident in understanding the relationships between Neanderthals and Homo sapiens.”

What’s next — This study team devised a robust method for dating the fossils of ancient peoples, such as the Neanderthals.

But if we truly want to understand the Neanderthals, other new, robust methods are needed too. This team suggests retesting the dates of other Neanderthal specimens using their compound-specific approach.

However, the ultimate question remains unanswered: What caused Neanderthals to disappear from the face of the Earth?

Researchers mention a few possible reasons — climate change, inbreeding, and competition from ancient hominins — but state that “these are beyond the scope of this article.”

Perhaps these new dating methods will help future paleontologists resolve that question, once and for all.

Abstract: Elucidating when Neanderthal populations disappeared from Eurasia is a key question in paleoanthropology, and Belgium is one of the key regions for studying the Middle to Upper Paleolithic transition. Previous radiocarbon dating placed the Spy Neanderthals among the latest surviving Neanderthals in Northwest Europe with reported dates as young as 23,880±240 B.P. (OxA-8912). Questions were raised, however, regarding the reliability of these dates. Soil contamination and carbon-based conservation products are known to cause problems during the radiocarbon dating of bulk collagen samples. Employing a compound-specific approach that is today the most efficient in removing contamination and ancient genomic analysis, we demonstrate here that previous dates produced on Neanderthal specimens from Spy were inaccurately young by up to 10,000 y due to the presence of unremoved contamination. Our compound-specific radiocarbon dates on the Neanderthals from Spy and those from Engis and Fonds-de-Forêt demonstrate that they disappeared from Northwest Europe at 44,200 to 40,600 cal B.P. (at 95.4% probability), much earlier than previously suggested. Our data contribute significantly to refining models for Neanderthal disappearance in Europe and, more broadly, show that chronometric models regarding the appearance or disappearance of animal or hominin groups should be based only on radiocarbon dates obtained using robust pretreatment methods.