Neanderthals

Neanderthals (sometimes spelled "Neandertals") are a type of extinct hominin closely related to modern humans. They are commonly classified as Homo neanderthalis. Originally thought to be a relatively primitive species displaced by more intelligent Homo sapiens, research has shown that Neanderthals, in fact, had well-developed cultural practices and behaviors akin to modern humans. Genetic studies have also shown that Neanderthals interbred with modern humans and may have had an impact on the DNA of most of the human population. Some scientists have even suggested they be considered a subspecies of Homo sapiens.

The fossil that gave the Neanderthals their name was found in Germany’s Neander Valley in 1856 in a cave being quarried for limestone. At least two Neanderthal fossils had been discovered before the Neander Valley individual; however, neither was recognized as a member of an extinct human group until after the name Neanderthal was assigned. Since then, many similar fossils have been found in scattered locations all over Europe and the Middle East. Dates assigned to the various fossils indicate that the Neanderthals originated around 400,000–200,000 years ago, and became extinct about 40,000–30,000 years ago, a few thousand years before the last glacial retreat. Thus, the Neander Valley specimen lent its name to a fossil relative of modern humans that occupied Europe and the Middle East late in the last Ice Age.

Though the Neanderthals were very similar to modern humans, they had several distinctive characteristics. Neanderthals were short and exceptionally stout bodied, with broad supportive bones and joints. This body form suggests a life filled with intense physical effort. Perhaps the compact body also helped them cope with cold stress under glacial conditions. Their brains were slightly larger than modern human brains. Their foreheads sloped up from their heavy eyebrow ridges, their jaws extended forward beyond the plane of the face, and their chins were weakly developed. These and several other characteristics are used to define a fossil as a Neanderthal.

Structure and Behavior

From the first identification of Neanderthals, scientists debated how to interpret the fossil evidence. German scientist Rudolph Virchow’s initial interpretation of the Neander Valley fossil as a diseased human was popular for a time. Virchow held that the fossil was a modern human whose unique features were the result of disease. However, as more fossils with the same characteristics were discovered throughout Europe and the Middle East, this explanation became untenable. In 1908, French paleontologist Marcellin Boule assembled a near-complete Neanderthal skeleton, generating additional debate over the species' status as a "missing link" in human evolution from apes. Misinterpretation of the characteristics of Neanderthal fossils, however, led Boule and others to interpret Neanderthals as stooped, bent-kneed, apelike subhumans with an animal nature to match.

Additional fossil discoveries, including evidence for toolmaking and burials, possibly with offerings, such as flowers placed in the grave, caused anthropologists to rethink the presumed animal nature of the Neanderthals. Although the evidence for flowers has been largely discredited, the evidence for burials, presumably accompanied by mourning, is accepted by most anthropologists. In addition, fossils showed that some Neanderthals lived much of their lives with deformed limbs and other disabilities, which would have made it difficult or impossible for them to fend for themselves. Yet they apparently lived many years in that condition, suggesting the support of other members of a social group. Such behavior was not in keeping with Boule’s picture of the Neanderthals as subhuman animals.

Reinterpretation of the anatomic evidence also suggested that, instead of a bent-kneed, stooped posture, the Neanderthals walked on two rather straight legs and had hands capable of manipulating materials and making tools, much as modern humans do. All this indicated that the Neanderthals were more like modern humans than Boule’s interpretation, and they came to be thought of in that light.

Taxonomic Relationship to Modern Humans

Neanderthals have always been recognized as close relatives of modern humans, but the specific taxonomy of the relationship is still a point of contention. Anthropologists place them in the same genus (Homo) as modern humans, but researchers debate whether they were members of our species, Homo sapiens (subspecies neanderthalensis), or constituted their own species, Homo neanderthalensis.

Such arguments are part of the practical taxonomy of the Neanderthals, but the real key to species identification and species separation is (at least theoretically) interbreeding. If the members of two groups can mate with each other and produce fertile offspring, and if these offspring can produce fertile offspring, the two groups are generally considered to be members of the same species. Therefore, the real taxonomic question becomes: Could Neanderthals and early modern humans interbreed? While genetic evidence from research in the 2010s strongly suggested interbreeding did take place, earlier studies often went back and forth on the subject. In the 2020s, most scientists agreed that interbreeding likely took place.

Because it is difficult to determine whether fossil groups interbred with one another, especially before reliable genetic studies were available, Neanderthal taxonomy has traditionally been primarily determined by anatomic and presumed behavioral characteristics, such as those already discussed. That taxonomy has vacillated with changing interpretations of those characteristics. Neanderthals have been placed in their own species for much of their history, but they have been identified as a human subspecies at other times. The latter designation implies that the Neanderthals and modern humans, Homo sapiens sapiens, were members of the same species and, therefore, could interbreed.

Determination of the Neanderthals’ taxonomic position is an integral part of arguments over the mechanism of the origin of modern humans. There are two main hypotheses for that origin: the replacement hypothesis of Christopher Stringer and the multiregional hypothesis vigorously supported by Milford Wolpoff. The replacement hypothesis is also called the "out of Africa" theory because it assumes that a population of anatomically modern Homo sapiens migrated out of Africa and expanded throughout Africa, Europe, and Asia, rapidly replacing the more primitive humanlike species living there, including the Neanderthals, which had migrated from Africa at an earlier date. Whether this replacement was by competition or by more direct and violent means is undetermined. The multiregional hypothesis suggests that earlier, more primitive ancestors of modern humans left Africa and dispersed, and these widespread populations evolved into modern humans separately, rather than being replaced by new immigrants.

Because the Neanderthals are the best-known and best-understood early human group, an understanding of the Neanderthal relationship is critical to an understanding of the evolutionary history of humanity. A Neanderthal contribution to modern human ancestry would support the multiregional hypothesis, and the lack of such a contribution would be consistent with the replacement hypothesis.

Advances of the Late Twentieth Century

By the 1990s, the Neanderthals were well established as a group related to modern humans, but questions remained: How close was the relationship? Did the two groups interbreed? Were Neanderthals a part of the evolutionary heritage of modern humans? During the 1990s, improved techniques and additional fossil discoveries led to greater understanding of Neanderthals but little consensus on these questions.

In a 1996 study, Jean-Jacques Hublin and several coworkers determined that Neanderthals found at an archaeological site in France made bone tools and wore decorative emblems on their bodies, behaviors not uncovered with older Neanderthal fossils. They concluded that the Neanderthals were influenced by early modern humans who lived in the same area at the same time and that a reasonably elaborate cultural exchange must have occurred between the two groups. However, based on the strikingly different anatomy of the two groups’ inner ears, they also concluded that the Neanderthals and modern humans did not interbreed. The investigators reasoned that if interbreeding had occurred, the two groups would have shared a common ear structure.

In 1997, Matthias Krings, Svante Pääbo, and their colleagues isolated and engineered deoxyribonucleic acid (DNA) from the mitochondria of Neanderthal bones and compared it to DNA from modern human mitochondria. They found the Neanderthal DNA to be quite different from that of modern humans and concluded not only that the two groups were different species but also that Neanderthals were not ancestral to modern humans.

In 1998, Daniel Lieberman proposed that a reduction in the length of the sphenoid bone during embryology can explain most differences between the two groups’ skulls. The sphenoid is a bone in the skull of both Neanderthals and modern humans, and Lieberman showed it to be shortened in modern humans but not in Neanderthals. He hypothesized that the impact of shortening the sphenoid resulted in the modern human skull characteristics, while the longer sphenoid resulted in the Neanderthal skull. Based on the fundamental nature of the change, he concluded that Neanderthals did not belong to the same species as modern humans and were probably not ancestral to modern humans.

In 1999, Cidàlia Duarte, Erik Trinkaus, and several colleagues discovered the buried remains of a four-year-old child in central Portugal. The skeleton was estimated to be about 24,500 years old, and they interpreted its anatomy to be a mixture of modern human and Neanderthal characteristics. Most anthropologists agree that southern Spain supported Neanderthal populations longer than other parts of the world, perhaps as late as 27,000 years ago, and that modern humans and Neanderthals coexisted in the region. Duarte, Trinkaus, and their group suggested that the skeleton they found demonstrated that the two groups did interbreed and that Neanderthals were part of the ancestry of Homo sapiens.

Discoveries of the Twenty-First Century

In 2007, Pääbo and Harvard Medical School geneticist David Reich began analyzing Neanderthal DNA, which Pääbo and his team had extracted from a forty-thousand-year-old fossil ten years earlier, to map the Neanderthal genome. At the time, when they had first studied the DNA, Pääbo's team had compared a piece of mitochondrial DNA from the Neanderthal fossil to the same piece of mitochondrial DNA from a modern human and found no appreciable similarities, thus lending credence to the replacement hypothesis. However, upon closer examination, Pääbo and Reich discovered that the Neanderthal DNA had certain similarities to the DNA of Europeans and Asians that were not evident between Neanderthal and African DNA. They determined that, on average, the DNA of modern Europeans and Asians was between 1 and 4 percent Neanderthal. Although this information conflicted with their previously held theories, Pääbo and Reich ultimately concluded that they had discovered evidence of interbreeding between humans and Neanderthals. They announced their findings in 2010.

Some scientists remained unconvinced by Pääbo and Reich's study. In 2012, Anders Eriksson and Andrea Manica of the University of Cambridge completed a study of the population structures of early humans in Africa. They concluded that modern humans and Neanderthals shared common African ancestors, who were not part of a genetically homogenous group but rather comprised several distinct populations. According to this model, these shared ancestors separated around 350,000 years ago, with one group migrating into Europe and Asia and another group remaining in Africa; subsequently, the former group evolved into Neanderthals, and the latter evolved into modern humans. Eriksson and Manica argue that such a shared ancestor, which they suggest may be Homo heidelbergensis, would account for the shared DNA, while a complex population structure in Africa would account for the disparity of DNA similarity between Africans and Eurasians.

Further research continued to develop the interbreeding theory. A 2016 study suggested an interbreeding event occurred approximately 100,000 years ago, well before the widely proposed "out of Africa" migration. Research published in 2017 pushed the date of DNA mixing between Neanderthals and modern humans even further back, to 130,000–145,000 years ago. In October 2017, a paper in the American Journal of Human Genetics refined the estimated amount of Neanderthal DNA in the genomes of most modern humans to 1.8–2.6 percent.

Not all research on Neanderthals focused on interbreeding with Homo sapiens. A study published in the journal Science in September 2017 presented evidence that Neanderthals' brains grew more slowly than those of other hominins. It was previously believed that a slow rate of brain growth, and the accompanying advantages in intelligence, were exclusive to modern humans, but Neanderthals showed even slower development. Other studies sought to reconcile the widely differing Neanderthal population estimates generated by fossil evidence (which suggested approximately 150,000 individuals) and early genetic research (which suggested only a few thousand individuals existed at most, and perhaps as few as one thousand in total). A September 2017 paper in the PNAS journal by Alan Rogers used genetic evidence to place the Neanderthal population in the tens of thousands.

Rogers also proposed a revised model of Neanderthals' timeline, suggesting they split from the ancestors of modern humans around 750,000 years ago. After entering Eurasia, the theory contends, these hominins nearly went extinct, causing a genetic bottleneck followed by division into Neanderthals and Denisovans. According to this model, Homo heidelbergensis and other European hominins of the time would be early Neanderthals.

In 2022, Svante Pääbo won the Nobel Prize for his research on Neanderthal DNA which provided key information about human immune systems, including information concerning human vulnerability to COVID-19. Pääbo and his research team also discovered a new ancient species, Denisovans, a sister group of Neanderthals. Though Pääbo's work occurred primarily in Siberia, other discoveries of Neanderthals in the early 2020s occurred globally, such as the Guattari Cave in Italy.

Significance

Although anthropologists have learned an enormous amount about the Neanderthals, their relationship to modern humans continues to escape consensus. This is, without question, a result of the difficulty of the problem and the tentative nature of the evidence. Most agree that the Neanderthals were a successful group closely related to modern humans. It is hoped that more fossils, improved technology, and fresh insight will clarify the question, because understanding the Neanderthals is likely to contribute to an understanding of humanity.

Principal Terms

Deoxyribonucleic Acid (DNA): The chemical that carries the instructions for all living things; closely related organisms have very similar DNA

Genus: The first part of the scientific name of an organism; members of the same genus but different species are closely related, but they cannot mate and produce fertile offspring

Mitochondria: Subcellular structures containing DNA used to estimate the relationships between groups of organisms; the more similar the DNA, the more closely related the groups

Species: The second part of the scientific name of an organism; members of the same species can mate and produce fertile offspring

Subspecies: The third part of a scientific trinomial, assigned to one of two groups that can mate and produce fertile offspring but have some strikingly different characteristics

Taxonomy: The science of classifying and naming living and fossil organisms, or the classification and scientific name of a living or fossil group

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