Modern Humans Genetic Code

The Neanderthals can be attested in the Near East just like the oldest modern humans outside of Africa. Modern humans might thus perhaps have been their neighbors, with whom they co-existed for more than 60,000 years, at least in the Levant. Which of the two human groups was there first—the Neanderthals from the north or the modern humans from the south—remains unclear for the present, but is not important in answering the question about the origin of Homo sapiens anyway. Light broke into the darkness of the two opposing theories in research results published in 1987 of mitochondrial DNA (mtDNA). This research has now been established as the "Black Eve" theory and has entered the history of paleogenetics. To give a brief summary, researchers demonstrated that the mitochondrial DNA of African women has the most variants and is therefore the oldest population of humans alive today. Mitochondrial DNA is only passed on through the mother's side, since a female egg cell is a complete cell, which contains tiny "power plants"—mitochondria— besides the cell nucleus, while the male seed only receives the cell nucleus in fusion. As the inherited material duplicates, mutations always appear, which have a larger impact on the mitochondria than they do on the cell nucleus. In the mtDNA there are thus demonstrably more mutations than in the cell nucleus DNA. For this reason, the female mtDNA is better suited to look for and determine differences, in order to make comparisons between nearly identical organisms, such as human beings.

As a result, mtDNA functions as a sort of molecular clock. The number of variations that can be established in the mtDNA of different people allows scientists to draw conclusions about the length of time that has passed since the permutation appeared. The examination of Australians, Europeans, Asians, and all other populations of humans living today has proven that they could have divided phylogenetically from each other only a short time ago. If one traces the mutation process back, it can be concluded that a primal "Eve" must have lived in Africa about 200,000 years ago. In family trees that were made to outline the mtDNA sequences, the African variants lie closest to the origin, which means that they display the most differences that can be established in the current world population; they certainly formed the pool of variants that all modern humans "tap."

The ancestress of all modern humans thus lived on the dark continent— so it makes sense to look for the primal father in Africa, too. The Y-chromosome is a region in the genome that offers the male counterpart to mtDNA; it is passed on exclusively from father to son. It is no surprise after the study outlined above to learn that studies of male genes have established that the primal Adam also came from Africa. With these two conclusions it is settled: the modern human originated in Africa and emigrated thence to the entire world, although possibly in several expansion phases (Figure 18).

But what does this mean for Neanderthal research? Not much at first glance, since the confirmation or rejection ofthe two theories through DNA analysis only goes to answer the question of where anatomically modern humans originated. But could DNA analysis be equally helpful in the question of possible interbreeding between modern humans and Neanderthals? That is one of the most-asked questions in paleoanthropology. The close proximity of find sites of modern humans (Skhul, Qafzeh, Figure 13c and Figure 23 in the Appendix) and Neanderthals (Kebara, Tabun) in Israel attest that the two hominid groups lived near each other without problems for at least 60,000 years. Such a long coexistence in the same region leads to the question of whether they might have met or even interbred. Traces of such possible interchanges would then be evident anatomically, if one recalls that the sturdy Neanderthal braved the ice age and the more lightly built Homo sapiens had fled the African sun. But all skull and skeleton parts that have been discovered have been—even though after some errors and confusion—classified either as clearly modern or clearly neandertholoid. It was only the discovery of the so-called "hybrid child" in 1998 at Lagar Velho in Portugal (Figure 20a) that gave new impetus to proponents of the interbreeding theory.

The nearly complete skeleton of a child about four years old, estimated at a geological age of c. 25,000 years, lay in a bed of burned pine twigs and was covered with red ochre—a typical modern human burial style (Figure 20a). Most of the anatomical characteristics also attest that this must have been a child of modern humankind. But a closer look reveals certain anomalous features that are more like those of a Neanderthal child. The receding lower jaw, the attachment points of the chest muscles, and the short, strong tibias suggest a hybrid population that lay between anatomically modern and Neanderthal humans. The find created a sensation in both the scholarly and the popular press for a long time. The Lagar Velho child suggests that modern humans indeed originated in Africa but would have interbred with the pre-existing archaic human types in other regions. But this thesis is not supported by the results of a study that Fred Spoor conducted of the Lagar Velho child's inner ear. He has proven that the position of the semicircular canals of the labyrinth in the child's inner ear is that of a modern human, not a Neanderthal. Whatever family affiliation is established for the supposed hybrid child with the help of new research methods, the result remains that local, sporadic interbreeding between human species like the Neanderthals and anatomically modern humans was not unlikely. Such a process would have repeatedly mixed the gene pools of the two populations. But then shouldn't we find traces of Neanderthal DNA in our genes? This is a question that can only be answered by the extraction of fossil DNA.

Today, the methods of paleogenetics permit time travel to the deepest depths of the genes of extinct organisms and living creatures whose DNA has survived in favorable environmental conditions, such as buried in ice

Figure 20 Burial rituals improve the probability of finding nearly complete human fossils. (a) The supposed hybrid child from Lagar Velho (Portugal) was laid to rest about 24,500 years ago, and excavated in 1998. (b) The approximately 60-year-old man from Sungir, Russia, was buried about 28,000 years ago with rich accessories consisting of 2936 individual pearls. Magnificent burials such as these can first be found with modern humans, not the Neanderthals.

Figure 20 Burial rituals improve the probability of finding nearly complete human fossils. (a) The supposed hybrid child from Lagar Velho (Portugal) was laid to rest about 24,500 years ago, and excavated in 1998. (b) The approximately 60-year-old man from Sungir, Russia, was buried about 28,000 years ago with rich accessories consisting of 2936 individual pearls. Magnificent burials such as these can first be found with modern humans, not the Neanderthals.

or in anaerobic bogs. The first study of the DNA sequence of a fossil human took place in 1997. The DNA came from the original Neanderthal from the Neander Valley. This 40,000-year-old fossil was granted the posthumous honor of donating a piece of its humerus for molecular study by Svante Pääbo, Matthias Krings, and Ralf W. Schmitz, the rediscoverers of the site of the Neanderthal's original discovery. It was possible to take mitochondrial DNA from the 3.5-gram sample, which was combined in a strand 379 base pairs long. A comparison of the fossil Neanderthal DNA with the DNA of humans living today showed an average of 27 divergences. That is a lot, since the sequences of a modern human show differences of only eight base pairs on average. What does this mean for the relationship between Homo sapiens and Homo neanderthalensis? The molecular biology periodical Cell declared on the significance of the study unequivocally: "Neanderthals were not our ancestors." Thus it appeared that the relationship between us modern humans and the archaic European from the Neander Valley had been made plain once and for all. But there was also some doubt about the published result. For one thing, impurities can always enter DNA samples; thus for example the DNA of the Neanderthal researcher Fuhlrott could have been mixed in the sample through a tiny hair. However, those in charge describe the sample as pure. The result might also have been different if the researches had used cell nucleus DNA, because nuclear DNA stores different information than mitochondrial DNA. But all of this is speculation. It is clear, on the basis of this epoch-making study, that the last common ancestor ofNeanderthals and modern humans must have lived about 500,000 years ago and that the last Neanderthals made no decisive contribution to the gene pool of humans alive today.

THE NEANDERTHALS' DEPARTURE

Although this result might have been crushing for many "Neanderthal fans," the achievement of Pääbo, Krings, and Schmitz cannot be overstated. We can eagerly anticipate further new interpretations, made possible through modern research techniques, which will continue to revolutionize paleoanthropology. These new methods include computer tomography and the study of isotopes, which permit conclusions about the morphology and diet of our forebears. The Zürich scientists Christoph Zollikofer and Marcia Ponce de Léon have shown themselves to be masters at the virtual reconstruction of human fossils by means of tomography and computer graphics. Without having to handle a fossil, the appearance of fossil humans like the Neanderthals can be recreated using rotating computer graphics. Parts of a fossil can be mirrored and inserted where the counterpart is missing, so that a complete picture of the organism can emerge. By means of stereolithography, plastic models can be prepared based on this foundation, which then serve reconstructors as the basis to make the most exact possible models of the soft tissues and features of the former living creature.

In the future, the TNT Project (www.The-Neanderthal-Tools.org) will provide access to this and other data. The internet platform offers laypeople and scientists alike access to data on the 300 Neanderthals found to date and their 130 find sites—an ambitious project that will also promote scientific democracy. For the first time, scientists from all over the world will be able to subject fossils to careful scrutiny that up to now have been largely inaccessible. The scientists' already limited travel budget will be spared, and an active exchange of data about fossils will be possible. Measurements of skulls, jaws, and bones can be undertaken on the internet as if directly.

All of these new processes, projects, and research methods place scholars in the fortunate position of being able to evaluate the old Neanderthals in ever new ways and perhaps to answer some of the unanswered questions about them. But whatever the method, paleo-anthropologists must always emphasize the significance of new fossil finds. Every new find represents a significant scholarly achievement in itself. Even Ralf W. Schmitz and Jürgen Thissen's rediscovery of the lost original find site of the Neanderthal in the Neander Valley and unearthing of new bone fragments of the skeleton appears as a small scientific miracle. One hundred and fifty years after Fuhlrott's description of the Neanderthal's discovery, today the additional find pieces have given the man from Mettmann a new face (Figure 1).

The chronology and find map of the last Neanderthals in Europe have also received a new face thanks to recent discoveries. For a long time it was assumed that the appearance of modern humans was accompanied by a pushing out of the Neanderthals into inhospitable, unfruitful regions such as the Iberian Peninsula. New finds could support this "ghetto" hypothesis. The Neanderthal fossils from Zafarraya in Spain are dated to an age of 28,000-32,000 years bp. Since there had been no later finds, it was assumed that, as the last Neanderthals, they lived in a sort of ghetto situation, until their population could no longer maintain itself. However, Vindija, a cave find site in northwestern Croatia, shows that during the same period there were still Neanderthal populations in other locations. The "youngest Neanderthals" found there, with an age of 28,000 years, lived in one of the most fruitful regions of central Europe—so the theory that they were forced out appears to have been thoroughly disproven. The stone tools discovered there, from the Mousterian and the Aurignacian (hitherto ascribed only to modern humans), also suggest that there was a peaceful interaction between Neanderthals and modern humans, which perhaps included even tool exchange—so the evidence does not support a forcible driving out and ghettoization.

Meanwhile, the picture of the Pleistocene interaction between modern humans and Neanderthals has been presented to the public as less peaceful. Thus as recently as spring 2000 a German news magazine published an article entitled "The War of the First Humans—How Homo sapiens Drove Out the Neanderthal." The entire title page was festooned with an illustration of two battle-maddened Europeans, a Neanderthal with eye ridges and brown eyes on the left and the modern human with long nose and blue eyes on the right. The Homo sapiens was presented as warlord and successful conqueror, who contended with the "rival" Neanderthals in a struggle for the better land, the better woman, and the better animals. Popular scientific literature often speaks of the "success model" Homo sapiens and of how he started his "triumphant progress" in the new world, becoming a creative sculptor and superior hunter. The "fate" of the Neanderthals is then for the most part described sadly, with frequent mentions of the "departure model" Neanderthal. With all of these platitudes, which rest on antiquated stereotypes of the stupid, inferior Neanderthal brute in contrast to the intelligent modern Herculean figures from Africa, the simple explanation for the disappearance of an entire species is not considered at all: like every other species in the animal kingdom, including humans, the Neanderthals had to produce enough offspring to maintain their population. Perhaps, though, the improved hunting weapons of Homo sapiens could also have been a reason why the latter species survived to the present day. Bloodthirsty speculations feed the desire for an image of a rivalry between Homo sapiens and Homo neanderthalensis that attracts readers and appeals to the martial spirit of our present age, but are of no use to science. If one sticks to the facts, it is clear that, even if we only consider the light population density of Europe, any sort of "war" between modern humans and Neanderthals would hardly have been possible.

The scenario according to which the Neanderthals were swept away by some insidious malady appears just as far from reality. Such an epidemic would have to have left behind concrete signs, but not a trace has been discovered so far. The Neanderthals were also well established in Europe's changing warm and cold climate in the ice age. Since in the period between 50,000 and 30,000 years BP there is evidence of a total of 18 climate changes that took place, the exit of the Neanderthals because of some sort of climatic catastrophe seems unlikely. So, what plausible explanation remains for the disappearance ofthe Neanderthals, a thoroughly successful human species? The theory that the Neanderthals died out due to a reproduction failure appears most probable. So-called "bottle-neck" situations, points of population restriction, are not unusual in human history and could thus also have affected the Neanderthals. In evolution, the extinction of a species is just as normal as the appearance of a new one.

What precisely led to the Neanderthals' disappearance can thus not be explained here. The only point that is certain is that there is no more evidence for Neanderthal existence after about 27,000 years bp. The last traces of this species have been found in the caves near Zafarraya in Spain and Vindija in Croatia that were mentioned above. More fossil remains of the last Neanderthals are the 31,000-year-old bones from Figueira Brava in Portugal, as well as the finds from Arcy-sur-Care and Saint Cesaire in France. Between 40,000 and 30,000 years bp, the Mousterian tool culture was already practically obsolete, and the finer Aurignacian had made its entry into Homo sapiens' stoneworking shops. At the same time as the "invention" of this technique, a cultural revolution took place that, as already mentioned, gave rise to the first figural art in the form of the lionman statue from the Swabian Hohlenstein-Stadel Cave or the horse carving from the Vogelherd Cave (Figure 21) or musical instruments like the bone flute from Geissenklosterle. But we can only speculate about how much this technological and creative wave also changed the Neanderthals' world.

For us "survivors," it is nonetheless important to recognize that we as Homo sapiens were not unique. Until 27,000 years ago we shared our territory in Europe with another human species, the Neanderthals. In southeast Asia, Homo sapiens even lived another 9000 years alongside another human species, Homo floresiensis (Figure 22). This totally unexpected species, discovered in 2004, has, like the Neanderthal, a different anatomy from the modern human. The dwarfish "hobbit" of Flores displays, with a volume of only 380 cm3, the smallest brain of all hominids in the human family "bush" found to date. Probably he was a descendent of very early African emigrants, who left Africa even before the Homo erectus, perhaps more than two million years ago. The find did not merely raise the spirits of its Australian discoverer. With the demonstrated existence of a new human species, the debate over the origins of the human family—between the "Out of Africa" theorists and the multiregionalists—flared up again. In any case, the fossils from Flores attest that human evolution can only really be understood when we pay attention not just to the anatomical and chronological classification of the finds, but above all to their geographical distribution too.

On different continents at different times, different developments took place that produced different human types more than once—like the

Neanderthals in Europe and the dwarf people of the island of Flores. We, Homo sapiens, are the remnant of all these regional developments— generalists, who increasingly specialized, invented agriculture, autos, and atom bombs, and populated the whole earth. Homo sapiens is a historian who has the ability to seek, discover, and interpret the evidence of his forebears and to share these findings with his fellow humans. As the last remaining human species, it is we who present the history and the image of the Neanderthals to the public. Today, 150 years after the discovery of the first fossil human bones to be identified as the remains of a Neanderthal,

Figure 22 Homo floresiensis, the little human from the Indonesian island of Flores, attracted worldwide media interest. Long after the last Neanderthal, the c. 18,000-year-old "dwarf" is further evidence that, beside the human group to which we belong, other types of humans existed. It is very likely that Homo floresiensis comes from a very old branching off from the earliest emigrants from Africa.

Figure 22 Homo floresiensis, the little human from the Indonesian island of Flores, attracted worldwide media interest. Long after the last Neanderthal, the c. 18,000-year-old "dwarf" is further evidence that, beside the human group to which we belong, other types of humans existed. It is very likely that Homo floresiensis comes from a very old branching off from the earliest emigrants from Africa.

we now know that the first Europeans have a long, exciting, and successful life story to tell. Neanderthals existed far longer than we have thus far, and therefore should receive from us a fitting place in the evolutionary model of becoming human. For we have not yet proven that we will be able to deal with the demands of our world longer and more successfully than our extinct fellow humans did.

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