Svante Pääbo Wins Nobel Prize for Deciphering the Neanderthal Genome
Svante Pääbo and friend -- Neanderthals are an extinct group of humans and the closest evolutionary relatives of humans living today. The oldest known Neanderthals are about 400,000 years old and they became extinct about 40,000 years ago. They lived in Europe, the Middle East, Central Asia and western Siberia. Their name comes from the site where workers in a limestone quarry discovered parts of a skull and bones in 1856 -- the Neanderthal near Düsseldorf, Germany. Although the skull was as large as that of human beings living today, it also showed clear differences. Compared to present day humans, the Neanderthals had more pronounced eyebrow bulges. Neanderthals also had a chinless face with peculiar nasal cavities, which made it easier to warm up cold air when inhaling. (Image Credit: Max Planck Institute for Evolutionary Anthropology - Leipzig)
Svante Pääbo Wins Nobel Prize for Deciphering the Neanderthal Genome
This year, the Nobel Prize for Physiology or Medicine went to Svante Pääbo, Director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Dr. Pääbo is no stranger to readers of Astromart News, as we have followed his work in early human genomics since 2009 when he and his team generated a first draft sequence for more than 60 percent of the Neanderthal genome. In 2014, his team succeeded in deciphering nearly 100 percent of the Neanderthal genome. This made a comparison with the genomes of today's humans possible. When Pääbo's team first published the Neanderthal mitochondrial genome, nothing seemed to indicate an exchange of genes between modern day humans and Neanderthals when they coexisted in close proximity. However, when Pääbo succeeded in deciphering the nuclear Neanderthal genome, it became clear that Neanderthals passed on large parts of their genome to modern humans. It turns out that one to three percent of the genomes of people living outside of Africa today stem from Neanderthals.
One of his most important scientific successes was the decoding of the Neanderthal genome. "His work has revolutionized our understanding of the evolutionary history of modern humans," said Martin Stratmann, President of the Max Planck Society. “Svante Pääbo, for example, demonstrated that Neanderthals and other extinct hominids made a significant contribution to the ancestry of modern humans.”
As early as the mid-1990s, Pääbo and his team were able to decipher a relatively short component of the mitochondrial DNA of a Neanderthal male. Mitochondria are tiny power plants in cells that supply them with energy and have their own DNA. This Neanderthal DNA differed considerably from the genome of modern humans. This proved that Neanderthals are not the direct ancestors of today's humans.
Since DNA sequencing methods became much more efficient in the early 2000s, Pääbo began sequencing the entire Neanderthal genome present in the cell nucleus.
A gigantic puzzle
The difficulty: After thousands of years, the bones of Neanderthals are so heavily colonized by bacteria and fungi that up to 99.9 percent of the DNA found in them originate from microbes. In addition, the small amounts of remaining Neanderthal DNA are only present in short fragments that have to be assembled like a gigantic puzzle. Many scientists believed that this task could not be solved.
However, Pääbo's team devised new solutions. The researchers worked under "clean room conditions" comparable to those in the chip industry. This enabled them to prevent the inadvertent introduction of their own DNA into the experiments. In addition, they developed more efficient extraction methods that improved the yield of Neanderthal DNA. Complex computer programs that compared the DNA fragments of ancient bones with reference genomes of chimpanzees and humans helped to reconstruct the Neanderthal genome.
In 2010, Svante Pääbo and his team succeeded in reconstructing a first version of the Neanderthal genome from bones tens of thousands of years old. Comparisons of the Neanderthal genome with the genomes of today's humans showed that modern humans and Neanderthals had produced common offspring at their meeting about 50,000 years ago, when modern humans left Africa and arrived in Europe and Asia.
Even today, the genome of today's non-African people still contains about two to three percent Neanderthal DNA. This genetic contribution influenced human evolution: it strengthened the immune system of modern humans, for example, but still contributes to their susceptibility to several diseases.
"Neanderthals are the closest relatives of humans today," said Svante Pääbo. "Comparisons of their genomes with those of modern humans and with those of apes enable us to determine when genetic changes occurred in our ancestors. In the future, it could also be clarified why modern humans eventually developed a complex culture and technology that enabled them to colonize almost the entire world. However, this required a more complete knowledge of the Neanderthal genome than the team had acquired in 2010.
Tracing human origins
In 2014, the team at the Max Planck Institute for Evolutionary Anthropology succeeded in deciphering the Neanderthal genome almost completely. This made a comparison with the genomes of today's humans possible. "We have found around 30,000 positions in which the genomes of almost all modern humans differ from those of Neanderthals and great apes," said Pääbo. "They answer what makes anatomically modern humans 'modern' in the genetic sense as well. Some of these genetic changes may be the key to understanding what distinguishes the cognitive abilities of today's humans from those of now extinct hominids.
Prior to this, Svante Pääbo's team had already achieved a sensation in 2012: They decoded the genome from a small bone found in the Denisova Cave in the Altai Mountains in western Siberia. The mysterious primeval humans were remotely related to the Neanderthals and contributed up to five percent to the genome of today's inhabitants of Papua New Guinea, Aboriginal Australia and other groups in Oceania.
The researchers are currently working on new methods to reconstruct DNA fragments that are even more decomposed and present in even smaller amounts. The aim is to enable research into even older DNA and genetic material from parts of the world where the survival of DNA is even rarer due to hot and humid climates.
What did Neanderthals look like?
Neanderthal bones were stronger, their pelvis wider and their limbs shorter. At a maximum of 1.70 meters, Neanderthals were not particularly tall, but of sturdy stature and strong, with a wide and deep chest - all adaptations to the cold climate of the Ice Age, which caused the Neanderthals' bodies to lose less warmth. The men weighed up to 90 kilos. Genetic analyses indicate that Neanderthals, like humans today, had different hair colors and skin tones. All in all, Neanderthals could mostly be distinguished externally from people living today by their unusual face.
Since brains do not petrify, the brain structure of early humans cannot be examined directly. Indirect clues do, however, exist: the shape of the skull. The internal volume of the brain skull shows that Neanderthals and modern humans had brains of similar size. Structures on the inside of the cranium reveal the shape of the basal brain and different lobes.
Using modern computer tomography, Jean-Jacques Hublin and his colleagues from the Max Planck Institute for Evolutionary Anthropology in Leipzig have taken three-dimensional X-rays of fossil skulls and created virtual impressions of the brain skull on the computer. This revealed that the temporal lobes of the cerebral cortex, which are involved in speech and memory, and the olfactory lobes of Homo Sapiens are larger than those of Neanderthals. This could indicate a better or differently functioning sense of smell in present day humans.
Neanderthals may have lived at a faster pace. They seem to have grown up faster than Homo Sapiens. For example, the enamel analysis of a Neanderthal child showed that their full dentition was completed one to two years earlier than the offspring of modern humans. The prolonged maturation period facilitates learning and possibly gave Homo Sapiens a decisive advantage over his cousin.
There were also differences in the development of the brain. At birth, Neanderthals and Homo Sapiens still have brains of about the same size and elongated skulls. While in modern humans the typical round skull form develops in the first year of life, this phase of brain development is missing in Neanderthals.
These differences have probably had an effect on the neuronal structure of the brain and thus on the mental, emotional and communicative abilities of Neanderthals. Some scientists therefore suspect that it is unlikely that Neanderthals have perceived the world the way we do.
Did Neanderthals have language?
Nevertheless, scientists assume that Neanderthals were also able to speak. At least the anatomical prerequisites for this seem to be given: The analysis of an inconspicuous bone of a 60,000-year-old Neanderthal showed that the hyoid bone of the Neanderthal was shaped in a similar way to the hyoid bone of today's humans. Many tendons and ligaments attach to the hyoid bone, providing the necessary mobility of the tongue for speech. Many researchers conclude from this that the Neanderthals were able to speak - whether in a primitive spoken language or a complex language like ours, however, cannot be said in this way.
Neanderthals, however, must have been able to pass on complex knowledge to their peers. This is indicated by many of their abilities, such as the production of sophisticated tools, the use of fire or group hunting of big game. Moreover, according to recent research, they seem to have mastered abstract thinking and used symbols such as paintings and body jewelry to communicate. There is even evidence that some of them buried their dead in graves. Genetic analyses carried out by scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig have also shown that some features of the protein encoded by the FOXP2 gene, which are important for language, are found also in Neanderthals.
Scientists have reconstructed the origin of Neanderthals on the basis of further bone finds in the 20th century: A lower jaw discovered as early as 1907 near Heidelberg is one of the oldest evidence of the presence of members of the genus Homo - so-called hominids - in Europe with an age of around 600,000 years. Jaws and teeth are anatomically a mixture between the African Homo erectus and the Neanderthal. Homo Heidelbergensis, sometimes classified as a species of its own, could therefore mark the transition between these two early humans.
Although hundreds of Neanderthal remains have been discovered, complete skeletons remain rather rare and most of them where found in the first half of the 20th century, when excavation techniques were rather rough. Accordingly, more than 150 years after the discovery of the Neanderthals, our knowledge about the lives of these people would still be even more incomplete if it had not been for the fact that some time ago new fields of research had made possible findings that were not thought possible: palaeogenetics and palaeoproteomics.
A pioneer in the field of palaeogenetics is Svante Pääbo. Together with his team at the Max Planck Institute for Evolutionary Anthropology in Leipzig, the scientist has developed new methods with which he can identify and analyze the genetic material that is sometimes still contained in bones that are thousands of years old. DNA comparisons between Neanderthals, modern humans and other early modern humans have helped clarify the origin and ancestry of the different human forms.
The DNA analyses carried out by Pääbo and his colleagues suggest that the lines of Neanderthal and Homo Sapiens separated about 600,000 years ago. In Africa, Homo Sapiens eventually emerged about 300,000 years ago. Neanderthals evolved in Europe and the Denisovans in Asia. The Neanderthals are therefore not the ancestors of today’s humans, rather they evolved parallel to them.
Until a few years ago, researchers assumed that this evolution took place independently of each other. Indeed, when Svante Pääbo's team first published the Neanderthal mitochondrial genome, nothing seemed to indicate an exchange of genes. However, when Pääbo finally succeeded in deciphering the nuclear Neanderthal genome, it became clear that Neanderthals passed on large parts of their genome to modern humans. As a consequence, one to three percent of the genomes of people living outside Africa today stems from Neanderthals.
In addition, the so-called Denisovans – an Asian relative of Neanderthals dicovered in 2010 by Johannes Krause and others in in Pääbo's team – passed on genes to the ancestors present-day Asians. Consequently, about five percent the genomes of people living Papua New Guinea comes from Denisovans.
Recently, Pääbo‘s team has found more evidence that different human forms mixed with each other. For example, when they investigated the DNA of the lower jaw of a modern human who lived about 40,000 years ago in Romania, they found that the proportion of Neanderthal DNA in this individual was so large that he must have had a Neanderthal ancestor between four and six generations back in his family tree. Even more strikingly, in 2018 Viviane Slon in the Leipzig team extracted DNA from a bone splinter from the Denisova Cave and found that it came from a female with a Neanderthal mother and a Denisovan father. This may suggest that Neanderthals and Denisovans produced children together relatively frequently when they encountered each other.
Genes from Neanderthals
Modern humans seem to have benefited from Neanderthal genetic variants. For example, researchers have discovered Neanderthal DNA segments that occur in modern humans and are responsible for the degradation of fats. Today, other Neanderthal genes strengthen our immune system. For example, variants of so-called toll-like receptors that are important for how the immune system is able to fight off infections have been contributed by both Neanderthals and Denisovans to modern humans and seem to have been of value as they have increased in frequency in Europe and Asia.
The brain development of modern humans has also been influenced by gene variants of Neanderthals. They have an effect on the shape of the skull and above all on brain areas for the planning and coordination of movements. The researchers found the strongest evidence for the effects of this Neanderthal DNA on gene activity in putamen, a basal ganglia, and in the cerebellum.
Our Neanderthal heritage also affects properties such as skin tone, hair color, sleep, mood, and even whether a person smokes. For example, people with certain Neanderthal variants smoke more frequently on average. So-called "night people" often also possess certain Neanderthal DNA. Scientists have compared Neanderthal gene variants in our genome with genetic information from a British database, which also contains personal data on appearance, nutrition, behavior and diseases.
The life of Neanderthals
As hunters and gatherers, Neanderthals were very mobile and probably roamed many thousands of square kilometers of land. They lived in small groups of no more than 50 to 60 women and men. As the genetic analyses show, even Neanderthals living several thousand kilometers apart were relatively closely related. Researchers conclude that early humans were rare most of the time. Even at a time when they were most widespread, there were probably no more than 10,000 Neanderthals throughout Europe.
Neanderthals have fed primarily on meat, as the analysis of amino acids in teeth and bones has shown. They were excellent hunters, killing even big game such as mammoths, bison and horses. But also vegetable food was certainly on their diet. Neanderthals were also technically adept. For more than 200,000 years there remains are associated with so-called Mousterian stone tools. The Mousterian sites contain tools such as side-scrapers, points and various types of flakes that were typically cut off from flint.
44,000 to 40,000 years ago, the Neanderthals finally developed the culture of the Châtelperronien. Until then, it was unclear whether Homo Sapiens or Neanderthals had created the tools and jewelry of this period. It was only through the combination of palaeoproteomics and palaeogenetics that Jean-Jacques Hublin and Svante Pääbo of the Max Planck Institute in Leipzig were able to prove that Neanderthals had produced objects that had previously been attributed to modern humans.
It is now known that they also created symbolic objects and paintings. Around 180,000 years ago, Neanderthals created a circle of broken stalactites in a cave in southwestern France, venturing over 300 meters deep into the cave. The function of this so far oldest known building of early humans is unknown.
Burial sites, on the other hand, indicate that they have dealt with death - all abilities that until then only Homo Sapiens had conceded to researchers. Since the oldest cave paintings, figures, decorated bone tools and jewelry known in Europe to date from the time of the so-called "Late Palaeolithic Revolution" some 40,000 years ago and Homo Sapiens immigrated to Europe during this period, many scientists assumed that these objects had been created by modern humans.
The art of Neanderthals
Thanks to a new dating method, researchers can now determine the age of lime crusts on paintings and objects. An international research team led by Dirk Hoffmann of the Max Planck Institute for Evolutionary Anthropology in Leipzig has used this uranium-thorium dating to investigate art from caves in Spain. According to the researchers, the paintings, are more than 64,000 years old and thus at least 20,000 years older than the earliest traces of modern man in Europe. They consist of simple geometric signs and handprints but do not yet include representations of animals. Naturally pierced shells, red and yellow pigments and containers with complex pigment mixtures from a cave in southeastern Spain were even dated by the researchers to be about 115,000 years old.
Inspired by Homo Sapiens?
The scientists conclude from this that not only Homo Sapiens, but also the Neanderthal could think abstractly and that his mental abilities might have been close to our own. Other researchers suspect, however, that Neanderthals did not produce sophisticated tools and body jewelry until Homo Sapiens arrived in Europe. They would not have produced sophisticated tools and body jewelry on their own initiative, but would have been inspired to do so only after contact with modern people.
Why the Neanderthals finally died around 40,000 years ago may never be certain. Likely the arrival of modern man in the mid-latitudes of Eurasia 45,000 years ago played an important role. Climate instability of that time period might also have accelerated the process.
Like father, like son
Svante Pääbo's father, Sune Bergström, was already honoured with the highest scientific award: the biochemist, together with Bengt Ingemar Samuelsson and Sir John Robert Vane, received the Nobel Prize for Physiology and Medicine in 1982 for their pioneering work on prostaglandins and related biologically active substances.
The Nobel Prize in Physiology or Medicine is one of the original five prizes donated by the Swedish inventor Alfred Nobel. It has been awarded annually since 1901 by the Swedish Karolinska Institute and is endowed with eight million Swedish crowns (approx. 775,000 euros). On 10 December, the anniversary of Alfred Nobel's death, the highest scientific award is solemnly presented by the Swedish King in Stockholm.
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