DNA analysis of 27 Neanderthals from Belgium and France found no evidence of extensive inbreeding, accumulation of genetic damage or late gene mixing with modern humans. The findings weaken the hypothesis that a gradual genetic collapse led to their extinction.
הNeanderthals They lived in Europe and western Asia for hundreds of thousands of years. They disappeared about 40 years ago, around the time of the spread of the modern manSeas across the continent.
Since then, researchers have been trying to understand why a human population that had managed to survive ice ages and severe environmental changes disappeared. One hypothesis has suggested that Neanderthal groups became small and isolated. According to this explanation, inbreeding and the accumulation of harmful genetic changes gradually weakened them.
The new study presents a more complex picture.
The researchers extracted genetic data from 27 Neanderthals who lived less than 52,500 years ago. The remains came from ten archaeological sites inBelgium And bFrance, including relatively dense sites in the Meuse River basin.
A new genome from about 45 years ago
One of the most important remains in the study came from the Goyet site in Belgium. The DNA preserved in it was of exceptionally high quality. As a result, the researchers were able to sequence its genome with an average coverage of 22.4 times.
“High coverage” means that each region of the genome is read many times. This reduces errors and allows for more confident identification of genetic variation, family relationships, and signs of population interactions.
The individual, dubbed GN1, lived about 45 years ago. His genome is only the fifth Neanderthal genome sequenced to date at high coverage.
Most other remains contained a much smaller amount of Ancient DNATo analyze them, the researchers developed an enrichment system called ArchaicPlus. It focuses on about 2.3 million points in the genome that provide information about the diversity of Neanderthals and Denisovans.
By combining the methods, the team was able to study a relatively large number of individuals from the same region and period, in contrast to previous studies, which were sometimes based on a single genome from a remote site.
Different groups, but not completely isolated
The comparison showed that most Neanderthals from Belgium and France were closer to each other than to Neanderthals of the same period from other regions of Europe.
Genetic closeness corresponds to the geographical distances between the sites. However, it does not necessarily indicate that all the individuals lived together or belonged to the same social group.
At the Goya site, for example, researchers found the remains of several individuals who were not close relatives. Previous studies have found signs on some of the bones that the bodies had been dismembered and that the individuals had been eaten. Isotope analysis also indicated that some of them did not grow up in the area where they were found.
Therefore, it is impossible to conclude that the remains represent a single family or local community. Nevertheless, the regional picture indicates connections between populations and the movement of people between different places.
The researchers suggest that periods of population expansion and contraction, caused by climatic changes, periodically connected groups living in northwestern Europe.
There is no sign of mating between first-degree relatives.
Studies of Neanderthals from the Chegirskaya and Denisova caves in the Altai Mountains have found very long stretches of DNA identical to both parents. Such stretches may indicate mating between close family members.
The GN1 genome did not contain an excess of these long segments. A similar pattern has previously been found in the Neanderthal genome from Vindija Cave in Croatia.
The findings do not mean that Neanderthals lived in large populations. Their genetic diversity was still lower than that of most modern human populations. However, at least in northwestern Europe, there is no evidence that mating between close relatives was common.
The groups may have been small, but they maintained contacts with other groups. Movement between sites and the exchange of mates could have prevented complete isolation.
Ancient dynasties survived side by side
The study also found signs of a more complex population structure. Most Neanderthals from the region belonged to a relatively common genetic group, but a few individuals carried remnants of earlier lineages.
One example is a Neanderthal tooth from the site of Coben in Belgium. Its mitochondrial DNA belonged to a very different lineage from that of most later Neanderthals in Western Europe.
The lineage is similar to that found in the Neanderthal known as “Thorin,” discovered in the Mandarin Cave in France. This raises the possibility that several Neanderthal lineages existed in Western Europe at the time.
However, the researchers emphasize that the quality of data from some of the remains is still low. More genomes will be needed to determine how widespread these ancient lineages were.
There is no evidence of modern human DNA that arrived shortly before
The Neanderthals studied lived at a time when modern humans had already arrived in parts of Europe. Some of the earliest modern humans have Neanderthal ancestors who lived only four to ten generations before them.
However, the picture in the opposite direction is different. The researchers did not find any long stretches of DNA originating from modern humans in the Neanderthal genomes they examined.
They identified some short segments that might be modern human, but these were too short to indicate admixture that occurred shortly before the individuals' lifetimes. They may result from much earlier contact between the populations or from shared genetic heritage.
The lack of evidence does not prove that there were no encounters or shared descendants. It is possible that some groups have not yet been sampled. It is also possible that mixed descendants have mostly integrated into groups of modern humans.
The finding highlights an asymmetry: Neanderthal genes survived in modern humans, but so far almost no modern human DNA has been found in the genomes of late Neanderthals.
No genetic collapse towards extinction found
The researchers also looked at whether the genetic condition of Neanderthals deteriorated as they approached the time of their disappearance. They compared early and late individuals and looked for an increase in deleterious changes, a decrease in genetic variation, or an increase in homozygous segments.
The tests found no such clear trend. There was no clear accumulation of harmful genetic load over time. Nor was there a consistent decline in genetic variation.
Therefore, the results do not support a model in which ongoing genetic deterioration was the main cause of Neanderthal extinction.
This does not fully solve the mystery of their disappearance. Small populations were still vulnerable to climate change, food shortages, disease, and competition with modern humans. Local events or periods of isolation could also have affected certain groups.
But the study shows that not all late Neanderthals should be described as a uniform, isolated, and degenerate population. At least in northwestern Europe, they belonged to a network of populations that were more connected and diverse than some of the genomes discovered in Asia suggested.
Questions and Answers:
How many Neanderthals were tested in the study?
The researchers generated genetic data from 27 Neanderthals from 10 archaeological sites in Belgium and France. Some of the genomes were partial, and one was sequenced to exceptionally high quality.
What is GN1?
This is the name given to the genome of a Neanderthal from the Goya site in Belgium, who lived about 45 years ago. It is the fifth Neanderthal genome to be sequenced at high coverage.
Did Neanderthals mate with relatives?
This may have occurred in some groups, but the new genome showed no signs of inbreeding, a finding that differs from results obtained in Neanderthals from the Altai region.
Is modern human DNA found in Neanderthals?
There was no evidence of genetic mixing that occurred shortly before the lives of the individuals examined. The possible segments found were very short and could result from much earlier contact.
Does the study explain why Neanderthals became extinct?
No. It rules out or weakens one explanation: gradual genetic decline as the main cause. The disappearance may be due to a combination of demographic, environmental, and competition factors with modern humans.
What does the research teach about the lives of Neanderthals?
He suggests that small groups could have been part of a wider regional network. Movement and connections between groups likely helped maintain genetic diversity and reduce inbreeding.
More on the subject on the science website
- A draft of the Neanderthal genome has been deciphered
- Neanderthal lineages reconstructed from the modern human genome
- Decoding the genome has yielded evidence of hybridization between Homo sapiens and Neanderthal man
- The Disappeared Neighbors: Neanderthal DNA and Us
- Neanderthals may have already carried the genetic basis for complex language
