Exploring the Surprising Genetic Diversity of Late Neanderthals

The last surviving Neanderthals in northwestern Europe may have lived in genetically diverse and closely interconnected groups, implying that inbreeding was not the primary cause of Neanderthal extinction approximately 40,000 years ago.

Research on Neanderthal genetics (Homo neanderthalensis) faces challenges due to a scarcity of well-preserved specimens for DNA analysis, with only four high-quality genomes available; three of these are from the fringes of the Siberian geographic range. These limitations mean that our understanding of their social structures is somewhat constrained. However, existing genomic data indicates that as Neanderthal populations dwindled, they may have become more inbred, potentially contributing to their decline.

Alba Bossams Mesa and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, sequenced DNA from 27 Neanderthal remains recovered from seven sites in Belgium and two in France, dating from 52,500 to around 40,000 years ago. One high-quality genome reveals that a woman was cannibalized in Belgium’s Goyet Cave about 45,000 years ago.

“These newly analyzed Neanderthal genomes are pivotal as they represent some of the latest known Neanderthals, offering fresh insights into their genetic diversity at the time of their extinction,” states Chris Stringer from the Natural History Museum in London.

Bossams Mesa and his team determined that these 27 remains corresponded to at least 11 different Neanderthals. Although all Neanderthals of this era were less genetically diverse than modern humans, there was no indication of an increased burden of harmful mutations or reduced genetic diversity.

This finding contrasts with other Neanderthal populations, such as those from the Altai region in Siberia, which displayed evidence of inbreeding. “These northwestern Neanderthals are closer to the time of their extinction and exhibit more genetic diversity than their eastern counterparts,” notes Bossams Mesa.

Genetic analyses further revealed that these Neanderthals were more closely related to each other compared to later Neanderthal groups in Croatia and southern Russia, diverging from a common ancestor approximately 54,000 years ago.

In broader terms, the Altai Neanderthals may not reflect the overall diversity of their species. Instead, the northwestern Neanderthals likely formed part of a larger, interconnected population, as noted by Bossams Mesa. Life and population histories among Neanderthals probably varied significantly across regions during periods marked by ecological and demographic transitions.

Modern humans appeared in Europe roughly 47,000 years ago and would have coexisted with these Neanderthal groups for numerous generations. Interestingly, the genomic analysis of these European Neanderthals shows no traces of modern human DNA, despite clear evidence of interbreeding occurring in other regions.

“This situation raises intriguing questions about the dynamics between Neanderthals and modern humans, which remain partially understood,” remarks Tarshika Vimala from the University of California, Berkeley.

Bossams Mesa suggests several theories could elucidate this finding. One possibility is that interbreeding primarily transpired in another area, such as the Levant. Alternatively, there may have been social factors or genetic incompatibilities that restricted the survival of hybrids within Neanderthal populations.

Stringer posits that the patterns of gene flow into modern human groups support his theory that late Neanderthals were losing reproductive viability to Homo sapiens, potentially leading to their extinction.

In a thought-provoking conclusion, Bossams Mesa suggests that the legacy of Neanderthals should not be regarded simply as extinction; “Even if traces of them remain in our DNA, they haven’t entirely disappeared,” she asserts.