Neanderthal fossils reveal signs of a devastating population collapse

Neanderthals once roamed large swaths of Eurasia for hundreds of thousands of years. Their skeletal remains are found across many excavation sites, yet their disappearance remains one of the biggest puzzles in human history.

Scientists at Binghamton University have uncovered fresh data that sheds light on a crucial population setback.

The study was co-authored by Professor Rolf Quam and graduate student Brian Keeling. The team analyzed fossils that point to a serious Neanderthal population dip around 110,000 years ago.

Ear fossils reveal Neanderthal history

The researchers examined the semicircular canals, anatomical structures in the inner ear that contribute to balance and reflect deeper genetic characteristics.

They compared the shape and variety of these canals in fossils from Atapuerca in Spain and Krapina in Croatia. These findings were compared with data from different regions in Europe and western Asia.

Differences observed in these canals indicated that early Neanderthals had a wider range of physical variation than their later counterparts.

The scientists concluded that this reduction was consistent with evidence of a bottleneck event in which genetic diversity plummeted.

Neanderthal population decline

Neanderthals are widely studied because they are closely related to us. Researchers have analyzed bones, DNA, and archaeological traces to figure out how these humans interacted with their environment and possibly with us.

Experts have proposed various reasons for their population losses, including small group sizes or changing climates.

One particular research strategy involves looking at the skeletal regions linked to genetics and see if the fossil record supports repeated reductions in group size.

“The development of the inner ear structures is known to be under very tight genetic control,” said Quam.

This makes the ear a reliable marker of underlying differences, since genetic changes there tend to stand out in the physical form of the canals.

When early Neanderthals show more diversity in their canal structure, it hints that they once had a broader genetic pool.

Lower diversity in their later phase points to a decline in numbers and possible isolation of different groups.

Insights from the fossils

Neanderthals appear in the fossil record around 250,000 years ago after branching off from earlier populations. They thrived in Europe and nearby areas for a while.

“We were surprised to find that the pre-Neanderthals from the Sima de los Huesos exhibited a level of morphological diversity similar to that of the early Neanderthals from Krapina,” said Alessandro Urciuoli, the lead author of the study.

The researchers found that older fossils from sites like Krapina displayed a wider variety of canal shapes compared to later Neanderthals. 

A population bottleneck can arise from shifts in food sources, environmental pressures, or other challenges that limit group size.

Fewer individuals mean fewer genetic variants get passed along to the next generation, so the population becomes less flexible over time.

Some researchers believe these crises happened multiple times in Neanderthal history. The new fossil evidence strengthens the idea that a key drop in variation took place around 110,000 years ago.

The mystery continues

Despite recent advances in DNA work, the story is far from finished. Certain sites that predate 100,000 years ago have given partial genetic data, but many specimens remain to be examined.

Scholars hope to learn if these bottlenecks were triggered primarily by changes in the environment or by interactions with other humans like our species.

Even more intriguing is whether brief population recoveries followed these drops or if decline continued until Neanderthals disappeared.

Keeling expressed excitement about the project and the methods used. “It is exciting to be included in this research project which relies on some of the latest cutting-edge methodologies in our field.”

Unknown extent of population decline

Investigating additional fossil collections across Eurasia could help determine the extent of this reduction.

Scientists want to see if certain groups survived by avoiding harsh environments or by exchanging genes with closely related populations.

With every new fossil discovery, more pieces of the Neanderthal puzzle come to light.

Experts remain curious about whether these humans adapted to their changing world enough to stave off extinction for thousands of years.

Ongoing investigations into the shape of ancient ear canals may continue to reveal how genetics guided the lives of these hardy populations. 

The study is published in Nature Communications.

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