Neanderthal evolution was more complex than previously thought

Scientists have been learning about Neanderthals for decades to find out where they fit in the history of human beings. These early ancestors of modern humans inhabited Europe and parts of Asia for hundreds of thousands of years. 

Although their physical, behavioral, and genetic characteristics have been well-established using fossils and artifacts, there is still controversy over their evolutionary history.

It was once believed that Neanderthals evolved slowly without major changes. New genetic and fossil studies challenge this idea.

Scientists have found big changes in Neanderthal diversity, suggesting a major event shaped their evolution. This discovery changes how researchers understand their origins and raises new questions about their development.

Emergence of Neanderthals

Neanderthals first appeared around 250,000 years ago. They evolved from earlier European populations called “pre-Neanderthals,” who inhabited the continent between 500,000 and 250,000 years ago. These pre-Neanderthals represent a crucial link in understanding how the species developed.

For a long time, researchers assumed that Neanderthals underwent little change during their evolution. Fossil records suggested a gradual transformation rather than a sudden shift.

However, recent studies reveal that their history involved major disruptions, including a drastic reduction in genetic diversity.

Genetic bottleneck in Neanderthals

Scientists studying Neanderthal DNA have uncovered evidence of a significant genetic loss.

This event, known as a “bottleneck,” occurs when a population experiences a severe decline in numbers, leading to reduced genetic variation.

For Neanderthals, this decline took place around 110,000 years ago. The discovery changes how scientists view Neanderthal evolution.

The genetic loss suggests they struggled to survive, possibly due to climate changes, environmental challenges, or other unknown reasons. Their population shrank, and only a small group contributed to the later Neanderthal lineage.

Studying Neanderthal diversity

Many researchers previously assumed that another bottleneck occurred much earlier, at the very start of the Neanderthal lineage.

They believed that early Neanderthals had lower genetic diversity than their pre-Neanderthal ancestors. However, paleogenetic data has not yet confirmed this idea.

A major challenge is the lack of ancient DNA old enough to confirm this event. Without it, scientists use other methods to check if an early genetic bottleneck happened.

This gap in data has fueled the search for alternative ways to study Neanderthal diversity.

Revealing evolutionary patterns

To overcome the limitations of DNA studies, researchers have turned to fossil morphology. The study was led by Alessandro Urciuoli and Mercedes Conde-Valverde, experts in human evolution. Urciuoli is a postdoctoral researcher at the University of Zurich.

The team analyzed the inner ear structure of Neanderthals. Specifically, they studied the semicircular canals, which play a key role in balance and movement.

The shape and differences in these structures help show genetic diversity. Since physical traits often match genetic diversity, this method helps study evolution when DNA is missing.

Genetic diversity of early Neanderthals

The experts examined two key fossil sites. Sima de los Huesos in Spain, which is 430,000 years old, has the largest pre-Neanderthal collection.

Krapina in Croatia, which is 130,000-120,000 years old, holds the most complete early Neanderthal fossils.

The researchers confirmed a major decline in Neanderthal diversity. Classic Neanderthals had much less variation in their semicircular canals than pre-Neanderthals and early Neanderthals.

The results of the study support earlier genetic research suggesting a population bottleneck.

“By including fossils from a wide geographical and temporal range, we were able to capture a comprehensive picture of Neanderthal evolution,” noted Conde-Valverde.

“The reduction in diversity observed between the Krapina sample and classic Neanderthals is especially striking and clear, providing strong evidence of a bottleneck event.”

This means that classic Neanderthals likely descended from a smaller, more isolated population. Their reduced diversity suggests that many genetic and physical traits became more uniform over time.

Rethinking the origins of Neanderthals

The study confirmed a later bottleneck but questioned whether Neanderthals started with low diversity. If an early bottleneck had happened, pre-Neanderthals would have had less diversity than early Neanderthals. Instead, scientists found the opposite.

“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. This challenges the common assumption of a bottleneck event at the origin of the Neanderthal lineage,” noted Urciuoli.

The research suggests that Neanderthal evolution was more complex than previously thought. Instead of a dramatic reduction at their origin, the early history of Neanderthals may have involved a stable and diverse population.

The findings raise new questions. If early Neanderthals were diverse, what caused their decline? Did climate, migration, or competition play a role? Further research may uncover the answers.

The study is published in Nature Communications.

Image Credit: Allan Henderson, under CC BY 2.0

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