Exeter, Devon UK • Dec 3, 2023 • VOL XII

Exeter, Devon UK • [date-today] • VOL XII
Home Science The fall of the Neanderthal

The fall of the Neanderthal

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The history of human evolution is a long and fascinating one. In this issue we look at one of our closest evolutionary cousins, the infamous Homo Neanderthalensis, more commonly known as Neanderthals. But how much do we know about Neanderthals and just how closely related are we? Neanderthals were an ancient species of Hominid, commonly recognised for their stunted, robust growth and distinct facial features, the enlarged forehead and protruding chin. They first emerged 500,000 years ago when they split from the Homo Sapiens Precursor Homo Erectus, living mainly in western and central Europe whilst modern humans lived mainly in Africa.

The first discovery of a Neanderthal, the imaginatively named Neanderthal 1, was in August 1856 when a selection of bones, including a skull fragment, were found in a grotto in Neanderthal, Germany. The area would later lend its name to the species. A full fossilised skull was later discovered in la Chappelle-Aux-Saints, France, estimated to be around 60,000 years old and showing the distinctive Neanderthal facial features. It wasn’t until the 1950s that full skeletons would be excavated from the Shanidar cave. Neanderthals were first suggested as a possible separate species to modern humans in 1846, when geologist William King suggested the Neanderthal fossil was sufficiently different from humans to warrant its own species. His name of Homo Neanderthalensis, after the location of the fossils discovery was then given to the species, beating German biologist Ernest Haeckel’s 1848 suggestion Homo Stupidus, the fun we could have had. Many sources depict Neanderthals as the primitive intellectual inferiors of our cavemen ancestors, however this is emphatically not the truth.

Neanderthals were first suggested as a possible separate species to modern humans in 1846

Archaeological finds prove that Neanderthals used stone and bone tools, made fires and may even have had some form of language, although this must have been fairly basic. Neanderthals may even have had access to water travel in the form of dugout canoes. Neanderthals lived in social groups, usually of five to ten related individuals, and evidence shows that they may even have had had some form of burial ritual. And while they may not be on the same level as their more successful cousins, who had a much larger toolkit and more complex social systems and trade, they were by no means as unsophisticated as commonly presented. Neanderthals died out about 50,000 years ago, the reasons for this are poorly understood although several theories have been put forward. Competition or even direct conflict with Homo Sapiens coming out of Africa and exposure to the new diseases they brought with them may have been partly responsible. Also, Neanderthals had much lower population sizes than humans so inbreeding may have been a much more common occurrence, leading to a build-up of harmful genes, an idea we will return to later. One alternative hypothesis suggests that Neanderthals failure to adapt to the changing conditions at the advent of the last ice age may be responsible for their extinction. Neanderthals may even have interbred and absorbed into the species we now call human.

In truth, we may never know conclusively what drove the Neanderthals to extinction: it could be any one of, or more likely a combination of the above factors. What we do know is that for approximately 5000 years before their extinction Neanderthals and Early Man shared Europe. During this time interbreeding occurred (likely on more than one occasion) and as a consequence some Neanderthal genes are present in modern day humans. That’s right: you may be part Neanderthal!

approximately 5000 years before their extinction Neanderthals and Early Man shared Europe

It is thought that Neanderthals account for between one and four per cent of genes in non-African populations. This may not seem a large amount but it becomes significant when you remember that there is a mere one per cent between us and Chimpanzees, our closest surviving relative. Recent research suggests that these genes may actually be harmful and are being weeded out by natural selection. This research was published in the journal PLOS Genetics and was carried out by researchers in the University of California. They looked at the distribution and abundance of Neanderthal genes within the human genome and found some interesting things. They found that fewer Neanderthal genes were found in gene dense regions of the human genome, suggesting that Neanderthal genes are selected against by natural selection. This may be because they are actually harmful. The study also showed a distinct lack of Neanderthal genes on the X-chromosome and none on the Y-Chromosome and mitochondria. This suggests that there may be a sexual element in the selection of these genes. It may even suggest that offspring of male Neanderthals were impossible or at least infertile, as the Y-Chromosome is passed exclusively down the male line. Neanderthal genes seem particularly common in areas of the genome associated with the immune system, this may be due to the need to adapt to new diseases as the coming together of two societies meant both were exposed to previously unseen pathogens It also has implications for our understanding of Neanderthals. In order for theses harmful alleles to be present they must have developed in Neanderthals. It seems likely that small population sizes lead to increased inbreeding.

fewer Neanderthal genes were found in gene dense regions of the human genom

This caused the build-up of these harmful alleles which in such a small population became effectively neutral, as there was no way of breeding out these harmful genes. When they get mixed into the much larger and more varied Homo Sapiens gene pool the most harmful genes get quickly selected against and disappear, leaving only those weakly harmful genes lingering in the most evolutionarily stable areas of the human genome. This suggests that over time Neanderthals may have become less “fit”, a measure of how well adapted or evolved a species is. The study calculated that Neanderthals had a high evolutionary “Load” (maybe even a 94 per cent reduction in fiitness). This may well have contributed to their extinction and is interesting to note that Neanderthal Skeletons show a high rate of fractures, developmental stress and degenerative diseases.

This is likely due to the lives spent hunting big game, but it may just be possible that harmful genes contributed, weakening bones and hastening the onset of diseases such as arthritis. So could it be that the Neanderthals gradually became less well adapted, and were driven to extinction by competition with our ancestors, who were more abundant, could run faster and were probably more intellectually advanced? That’s one possible conclusion, but in truth, we may never know.

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