Genomic Data Reveal a Complex Making of Humans

Mitochondrial DNA from Neanderthals has not been found in humans and genetic evidence suggests that male humans and female Neanderthals did not mate. Human-Neanderthal admixture was extremely rare at the time and it is likely to have taken place in some forms of rape by Neanderthal males who encountered female H. sapiens on rare occasions and their offspring contributed to spreading Neanderthal DNA among AMH. Male humans may not have found female Neanderthals attractive or female Neanderthals were protected by stronger Neanderthal males, making them unavailable for male H. sapiens.

Studies have shown though that modern humans share a common male ancestor who lived 59,000 years ago. Could this male ancestor have been Neanderthal? Indeed, the date of our closest common male ancestor correlates well with estimations of gene flow between Neanderthals and humans around 50,000 to 80,000 years ago. If H.neanderthalensis and H.sapiens were able to mate, then it is plausible that only the male H.neanderthalensis and the female H.sapiens were able to produce fertile offspring. The reciprocal cross may not have been successful.

According to Haldane’s law, the heterogametic offspring of interspecific hybrids are likely to be absent, rare, or sterile (Short, 1997). If Haldane’s Law applied to the offspring of H.neanderthalensis and H.sapiens, we would expect to find female hybrids quite commonly, but male hybrids much more rarely. The male hybrids would have carried a Y chromosome very similar to that of the original hybridizing male. The lack of Neanderthal mtDNA suggests that the initial hybridization involved a Neanderthal male, but there would probably have been few if any male hybrid offspring, so the Neanderthal Y chromosome and the mtDNA would have been quickly lost. Nonetheless, the Neanderthal autosomes would have happily mingled and interchanged with human autosomes, eventually losing their identity in the process.

Could it be that Homo neanderthalensis males were able to mate with Homo sapiens females but that the reciprocal cross was unsuccessful? Alternatively, were male H.sapiens disastrously incapable of wooing the physically more powerful H.neanderthalensis females? Or were H.neanderthalensis females simply unable to give birth to hybrid offspring? Perhaps male H.neanderthalensis outcompeted early male H.sapiens and eventually the male Neanderthal genes gained dominance (and maybe H.sapiens females somehow out-competed H.neanderthalensis females for partners). All of these possibilities potentially explain how we share a common male ancestor 59,000 years ago, but a common female ancestor 170,000 years ago. Simultaneously, these hypotheses explain why comparisons of DNA sequences in mitochondrial DNA from Neanderthals and modern humans have indicated that there was no interbreeding between these two exceedingly similar species (Potts & Short, 1999:59). Mitochondrial DNA from Neanderthals simply may not have made it into the modern human lineage. The nuclear DNA of Neanderthal males, however, possibly did.

blogs.plos.org/neuroanthropology/2010/10/26/the-neanderthal-romeo-and-human-juliet-hypothesis/



Figure 1. Schematic presentation of the six models.

The third models correspond to an ancestral population which gives rise to three sub-populations: one in the West, another in the East and one in the South (fig. 1, table 1). This southern population corresponds to the paleoanthropological hypothesis concerning the presence of a Southern population [3], [15]–[18]. According to the geographical barriers and morphological evidence, we have established three different divisions. The fossil of El Sidron from a paleogeographic standpoint is closer to French fossils than to Italian and Croatian fossils. On the basis of morphological data it might be closer to the southern fossils (model 3b). Due to its geographical position, the fossil of Mezmaïskaya, discovered in the Caucasus, might be placed either in the eastern (model 3a) or in the western group (model 3b and 3c). These divisions are shown in table 2. For model 3 (a, b, c) we made the same assumptions as in model 2 regarding population growth, migration, population sizes, and generation time. Forty eight simulations of this model have been tested, sixteen by grouping. Most measures of genetic diversity fit the observed measures more closely than in the previous models. Indeed, if we consider a growing population in which migration occurs, we see plausible and best values of P(Co|C) for all models (3a, 3b and 3c) for simulation sets with twelve or nine sequences. The most precise fit is that of model 3c, which presents values of P(Co|C) closest to 0.5 (table 1). If we consider a growing population with no migration, only model 3c presents the best values of P(Co|C). Thus models three, which posit three groups among Neanderthals, and assume a growing population, seem to be most realistic, and model 3c is the most plausible one.


Figure 2. Map representing Neanderthal geographical distribution in groups.

Models three and particularly model 3c are also statistically the strongest models. Moreover, they are coherent with the paleoanthropological data. Neanderthal features favour a distinction between western and eastern Neanderthals, with the western populations presenting more derived features than the eastern groups [13], [14]. This distinction has been explained by a migration to the East during the isotopic stages 5 or 6 [12], [14] or by a phenomenon like isolation through distance [40]. The sequence of Mezmaïskaya (in the Caucasus) is thus located in an intermediate region and could be placed in either of these groups. According to the geographical position of this fossil, this sequence could also belong to still another group. In the state of our knowledge, however, we are unable to test this assumption, since we need at least two sequences to establish a group. These models, 3a, 3b and 3c, also support previous paleoanthropological studies of the phylogenetic position of the fossil remains of Okladnikov in Siberia [26]. This fossil has been identified as a Neanderthal on the basis of its nucleotide sequence. Our results situate this fossil in the eastern Neanderthal group.

Our results clearly favour the existence of one southern group which is present throughout model three. Our models 3b and 3c differ in regard to the position of El Sidron (northern Spain). According the model 3b the fossil of El Sidron is located in the southern group, wheras the model 3c situates it in the group extending from Spain to Belgium. In addition, we supposed that sequences of Monte Lessini in Italy and Vindija in Croatia allow to the same group because it exists a morphological closeness. This can be explained in terms of eco-geographical factors. Indeed these two regions are isolated in the north by the Alps and, in the range of datings that we consider for these sequences, a marine regression offers an easier passage between northern Italy and Croatia.

www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0005151

This Wednesday, Oct. 9, 2013 photo shows the stone age recycling site cave at the north of Israel next to the city of Zichron Yaakov.

From caves in Spain and North Africa to sites in Italy and Israel, archaeologists have been finding such recycled tools in recent years. The conference, titled "The Origins of Recycling," gathered nearly 50 scholars from about 10 countries to compare notes and figure out what the phenomenon meant for our ancestors. Recycling was widespread not only among early humans but among our evolutionary predecessors such as Homo erectus, Neanderthals and other species of hominids that have not yet even been named, Barkai said.

Avi Gopher, a Tel Aviv University archaeologist, said the early appearance of recycling highlights its role as a basic survival strategy. While they may not have been driven by concerns over pollution and the environment, hominids shared some of our motivations, he said. "Why do we recycle plastic? To conserve energy and raw materials," Gopher said. "In the same way, if you recycled flint you didn't have to go all the way to the quarry to get more, so you conserved your energy and saved on the material."



At Qesem cave, a site near Tel Aviv dating back to between 200,000 and 420,000 years ago, Gopher and Barkai uncovered flint chips that had been reshaped into small blades to cut meat—a primitive form of cutlery. Some 10 percent of the tools found at the site were recycled in some way, Gopher said. "It was not an occasional behavior; it was part of the way they did things, part of their way of life," he said. He said scientists have various ways to determine if a tool was recycled. They can find direct evidence of retouching and reuse, or they can look at the object's patina—a progressive discoloration that occurs once stone is exposed to the elements. Differences in the patina indicate that a fresh layer of material was exposed hundreds or thousands of years after the tool's first incarnation.



Participants in the conference plan to submit papers to be published next year in a special volume of Quaternary International, a peer-reviewed journal focusing on the study of the last 2.6 million years of Earth's history. Norm Catto, the journal's editor in chief and a geography professor at Memorial University in St John's, Canada, said that while prehistoric recycling had come up in past studies, this was the first time experts met to discuss the issue in such depth. Catto, who was not at the conference, said in an email that studying prehistoric recycling could give clues on trading links and how much time people spent at one site.



Recycling bones in the Middle Pleistocene: the early cases of Gran Dolina TD10-1 (Spain), Bolomor Cave (Spain) and Qesem Cave (Israel). Jordi Rosell, Ruth Blasco et. al. Area de Prehistoria, Universitat Rovira i Virgili (URV), Tarragona, Spain and IPHES, Institut Català de Paleoecologia Humana i Evolució Social, Tarragona, Spain.

Archaeologists have used different kinds of data to identify recycling. Most approaches to recycling are based on lithic artifact attributes, and especially on surface alterations, that suggest a period of discard between different activity events. But, recycling can be also approached by means of faunal remains from bone damage. The bone breakage processes generate a high number of small and large-sized fragments, which are usually discarded. However, some of these rejected elements can show suitable morphological characteristics to be used for different purposes. On this basis, it is necessary to distinguish between the use of bone raw material from pre-existent carcasses of elephants (and other large animals) and recycling of fragments resulting from the extraction of marrow contained in bones. In the first case, bones are considered as raw material similar to lithic industry. In the second one, bones are not fractured with a technological purpose, but they are selected to be used in a subsequent process. Here we present some early cases of recycled bones from the Middle Pleistocene sites of Gran Dolina TD10-1 and Bolomor Cave in Spain and Qesem Cave in Israel. The studied elements seem to have been part of a previous faunal processing sequence (with nutritional objective) and later, they seem to have been selected among rejected items to be used or modified intentionally. These fragments are dated to MIS 9 and show bone damage produced by use (retouched and unmodified soft hammers) or present configured forms (bone artifacts). With this study, we try to provide data on the recycling activities on faunal remains in the Middle Pleistocene and discuss on the origin of this behaviour.

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