Paleolithic Neanderthal Research: Correlation with Homo Sapiens

A widely accepted fact is that genus of Homo neanderthalensis is found in Europe and Asia for a period from 500,000 years ago, up to about 30,000 years ago. Relationships with the anatomically modern man resulted in an intense controversy over the differences between these two species. However, their distinctive morphological features have now led to Neanderthals' recognition as a species different from that of Homo sapiens, which evolved in Eurasia. Nevertheless, a relationship between those is recognized, as they are considered to have been descended from a common ancestor. Although the two species have a long coexistence period in the Middle East (Akazawa T. et al. 1998), the presence of Homo sapiens in Europe is set at around 40 ka BP (thousand years before present). This process of migration has raised a number of questions about the relationship between the two species as well as the cause of the Neanderthals' extinction. The extinction period of the species has been set at around 40 to 30 ka BP, previously reinforcing the hypothesis that the main reason for this was its confrontation with the newly introduced inhabitants of the continent.

Figure 1: A modern human and a Neanderthal skull facing each other.

Some of the possible causes of Neanderthal extinction are inextricably linked with their correlation with modern man. There are two established theories within the scientific community regarding the origin of Homo neanderthalensis and its separation from Homo sapiens as a species. One of these theories could shed light on the circumstances under which Neanderthals came to exist. As these theories are examined, some important positions and dates will be presented, which may be related to the extinction of the Neanderthals.

The first theory holds that Neanderthals crossed with Homo sapiens on a relatively large scale. Proponents of this theory believe that although Neanderthals as organisms no longer exist, the first modern humans had some of the same genes that may still exist today (Pääbo, 2015). Neanderthal DNA was present in smaller quantities, due to the large quantitative difference between Homo neanderthalensis and Homo sapiens populations. According to this theory, Neanderthals were a subspecies of Homo sapiens and not a separate species, therefore, their scientific name should be Homo sapiens neanderthalensis. The proponents of this theory cite as evidence two paleoanthropological findings.

They are initially based on the fact that Neanderthals are found in some Cro-Magnon populations, which are the first Homo sapiens in Europe and take their name from the eponymous refuge found in France in 1868 (Stringer, C. and Gamble, C., 1998). For example, researchers studying the skeleton of a modern boy from Lagar Velho in Portugal claim that, although the morphology of the pelvis and face similar to that of Homo sapiens, the strength and proportions of the limbs are more similar to Neanderthals (Trinkaus, E. & Zilhão, J., 1999). As the skeleton dates back to the time of the last known Neanderthal, these features must represent important interconnection and DNA transmission between modern humans and Neanderthals.

The fossil remains were discovered on November 28, 1998 during an expedition to the Abrigo do Lagar Velho to study some previously discovered cave paintings. However, it was not until April 1999 that the great discovery in Lagar Velho, Portugal, was announced (Trinkaus, E. & Zilhão, J., 1999): a human skeleton belonging to a boy of about 4 years of age, buried in a deliberate manner. The reconstruction of the site shows that the burial place was an accumulation of sediment, surrounded by the bank of the Sirol river. The authors of the discovery, the Portuguese João Zilhão and the American Erik Trinkaus, both experts on Neanderthals, believed that the skeleton was a hybrid subject between Neanderthal and Cro-Magnon Man.

Figure 2: Skeleton of Lagar Velho boy.

At the same time, there are features of the modern man found in younger Neanderthal populations. The Neanderthals of Vindija Cave in Croatia look more modern than other Neanderthals, suggesting that they may have crossed with the incoming Homo sapiens (Green et al., 2010). The remains of Neanderthals were found in the context of Mousterian stone carvings, a neanderthalian style, but also with elements of Aurignacian, which is characteristic of the first Sapiens. The possible connection of Neanderthal palaeontological finds with stone carvings connected to Sapiens, brings back to the fore theories about the chronological coexistence of the modern humans and Neanderthal populations. The assimilation of the lithographic and cultural elements introduced by the first Eurasian in the West is also examined. These findings were originally dated 28,000 years before the present, which would mean further relations between the two species in this area. However, the new dating generated in 2017, with more technologies, shows that these are paleoanthropological findings dating from 44,000 years before the present (Devièse et al., 2017) .

On the other hand, there are some other researchers who have a different view on the separation of species. According to them, Homo neanderthalensis was essentially replaced by Homo sapiens. In this case, Neanderthals are a separate species from Homo sapiens. This model allows crossbreeding between the two species, but there is no significant genetic influx from Neanderthals to modern Europeans (Mafessoni, 2018). This is due to the quantitative difference between the two populations.

Figure 3: Neanderthal bone found at Vindija Cave, Croatia.

Proponents of that case have been working to make the actual transcript of this statement available online. First, Neanderthal mitochondrial DNA is different from that of modern humans. This emerges from research first conducted in 1997 (Relethford J., 2010). In addition, an analysis of nuclear DNA and Neanderthal genes released in 2010 shows that the two species began to diverge about 600,000 years ago. It also shows that there have been small crosses, as non-Africans have 1% to 4% in common with Neanderthals. Moreover, studies of the growth patterns of young Neanderthals show that they grew in different ways than Homo sapiens. On May 2010, following the genome sequencing of three Vindija Neanderthals, a draft sequence of the Neanderthal genome was published and revealed that Neanderthals shared more alleles with Eurasian populations than with sub-Saharan African populations (Green et al., 2010). The observed excess of genetic similarity is best explained by recent gene flow from Neanderthals to modern humans after the migration out of Africa.

Be that as it may, these two views are passionately supported by their proponents in discussions regarding species separation. what is considered important for this issue, however, is that there were undoubted crosses between Neanderthals and modern humans, which due to quantitative differences led to the assimilation of the species by a percentage. However, this is not the only reason for their disappearance, as there is still a lot of data to be examined.

Research regarding the interaction of Neanderthals with other human species are still ongoing. The time period during which they came in contact with each other is constantly changing with the data being turned upside down at regular intervals. Until 2019, there was a perception that Neanderthals and modern humans coexisted only for 5,000 years, with their disappearance dating back to 38,000 years before the present. However, in 2019 a better analysis was performed on skulls found at the location of Apidima of Mani in Greece (Harvati K., 2019). While originally regarded as Neanderthal paleontological remains, it was eventually adopted that they belonged to modern humans, dating to 210,000 years ago. This implied a longer period of coexistence between both species.

In an area as vast as Europe and in such a long time, all kinds of interactions would have been possible - from hostilities to peaceful coexistence, and from trade to mixing. The Neanderthals came into contact with both the Cro-Magnons and a species that came to the fore relatively recently, the Denisovans. It is a species whose first remains were found in the Altai Mountains in Siberia in 2010, when a bone was discovered. Based on the analysis of genetic material extracted from a girl from the same area and dating to 90,000 years ago, it emerged that she had shared genetic material with both Denisovans and Neanderthals (Warren M., 2018). Therefore, this study proves that there were crosses between the two species. In addition, remains of Denisovans, Neanderthals, and modern humans have been found in the Altai Mountains. However, it is not certain whether they shared this territory at some point. The only thing that can be confirmed is that there were crosses between these species.

Figure 4: Impression of a young female Denisovan, based on skeletal traits derived from ancient DNA.

There are many examples that have made it necessary to investigate a genetic relationship between Neanderthals and modern man. The existence of some morphological elements found even in present-day humans, indicating a connection with Neanderthals is one of them. These include the presence of similarities in some cranial elements, such as the broad cranial dome, the protruding supraspinatus arch and the wide cavity of the nose. These morphological elements represent alleles of the genetic code, which according to Frayer (Pearson, 2004) are gradually declining (from the Upper Paleolithic to the present), but, nevertheless, some survive. This phenomenon indicates the presence of interferences between Neanderthals and Homo sapiens.

To conclude, Homo sapiens were numerically superior and possibly managed to assimilate Neanderthals. Homo Neanderthal disappeared abruptly. Nevertheless, the fact that one of the reasons for their replacement by modern man was the close relationship they had with other species cannot be ruled out. Researchers hypothesize that Neanderthals may have become isolated into small groups during harsh climatic conditions which contributed to inbreeding behaviours (Vaesen, K. et al. 2019). Due to the lack of genetic diversity, Neanderthal populations would have become more vulnerable to climatic changes, diseases and other stressors which may have contributed to their extinction. A similar model to the inbreeding hypothesis can be seen among endangered lowland gorillas (Hedrick, P., & Kalinowski, S., 2000). Their populations are so small that it has caused inbreeding, making them even more vulnerable to extinction. This case is one of many related to the causes of Neanderthal extinction, but it is also one of the most widespread. It is possible, in addition to other potential causes that will be analyzed in the following chapters, that this case may have contributed to the situation.

References:

Akazawa, T., Aoki, K., & Bar-Yosef, O. (2005). Neandertals and modern humans in Western Asia. Plenum Publishers.

Devièse, T. et al. (2017). Direct dating of Neanderthal remains from the site of Vindija Cave and implications for the Middle to Upper Paleolithic transition. Proceedings Of The National Academy Of Sciences, 114(40), 10606-10611. https://doi.org/10.1073/pnas.1709235114

Green, R. et al. (2010). A Draft Sequence of the Neandertal Genome. Science, 328(5979), 710-722. https://doi.org/10.1126/science.1188021

Harvati, K. et al. (2019). Apidima Cave fossils provide earliest evidence of Homo sapiens in Eurasia. Nature, 571(7766), 500-504. https://doi.org/10.1038/s41586-019-1376-z

Hedrick, P., & Kalinowski, S. (2000). Inbreeding Depression in Conservation Biology. Annual Review Of Ecology And Systematics, 31(1), 139-162. https://doi.org/10.1146/annurev.ecolsys.31.1.139

Mafessoni, F. (2018). Encounters with archaic hominins. Nature Ecology &Amp; Evolution, 3(1), 14-15. https://doi.org/10.1038/s41559-018-0729-6

Pääbo, S. (2015). Neanderthal man (p. 237). Basic Books.

Pearson, O. (2004). Has the combination of genetic and fossil evidence solved the riddle of modern human origins?. Evolutionary Anthropology: Issues, News, And Reviews, 13(4), 145-159. https://doi.org/10.1002/evan.20017

Relethford, J. (2013). The human species. McGraw-Hill Humanities/Social Sciences/Languages.

Trinkaus, E. & Zilhão, J. (1999). The early Upper Paleolithic human skeleton from the Abrigo do Lagar Velho (Portugal) and modern human emergence in Iberia. Proceedings Of The National Academy Of Sciences, 96(13), 7604-7609. https://doi.org/10.1073/pnas.96.13.7604

Vaesen, K., Scherjon, F., Hemerik, L., & Verpoorte, A. (2019). Inbreeding, Allee effects and stochasticity might be sufficient to account for Neanderthal extinction. PLOS ONE, 14(11), e0225117. https://doi.org/10.1371/journal.pone.0225117

Warren, M. (2018). Mum’s a Neanderthal, Dad’s a Denisovan: First discovery of an ancient-human hybrid. Nature, 560(7719), 417-418. https://doi.org/10.1038/d41586-018-06004-0

Image References:

Figure 1: Baxter, M. (2008). Comparison of Modern Human and Neanderthal skulls from the Cleveland Museum of Natural History. [Photo]. Retrieved from : https://australiascience.tv/battle-of-the-brains-neanderthal-vs-homo-sapien/

Figure 2: Zilhão, J. (2011). Skeleton of Lagar Velho boy. [Photo]. Retrieved from: https://www.researchgate.net/publication/285527403_Chapter_6_The_emergence_of_language_art_and_symbolic_thinking

Figure 3: Higham, T. (2017). Neanderthal bone found at Vindija Cave, Croatia. [Photo]. Retrieved from: https://phys.org/news/2017-09-dating-neanderthal-vindija-cave-older.html

Figure 4: Harrel, M. (2019). Impression of a young female Denisovan, based on skeletal traits derived from ancient DNA. [Visual Painting]. Retrieved from: https://www.nationalgeographic.com/science/article/dna-reveals-first-look-enigmatic-human-relative