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Post by Admin on Oct 6, 2017 18:58:19 GMT
Nubians are an admixed group with gene-flow from outside of Africa The Nubians inhabit the Nile valley in the arid desert of northern Sudan and speak Eastern Sudanic languages of the Nilo-Saharan linguistic family that are close to the languages spoken by Nilotic populations (Table 1, Fig 1A). The Nubian populations have a long history in the region, dating back to dynastic Egypt [5]. They showed little genetic differentiation among individuals and groups, with a maximum (across all pairwise comparisons) pairwise FST (Weir and Cockerham’s estimator) of 0.004513 between the Mahas and the Halfawieen (Fig 1B, S7A Fig). The FST values to the surrounding Arabic and Beja populations were also low, which hints at gene-flow or shared ancestry with the neighboring populations. Even though the Nubians and the Nilotes are linguistically closer to each other than to the Afro-Asiatic groups, the Nubians showed the greatest genetic differentiation (FST between 0.02 and 0.04) to the Nilotes (Fig 1, S7A Fig). To investigate whether this signal of genetic differentiation is driven by the Eurasian admixture into the Nubians (as seen in Fig 2), we created pseudo-‘unadmixed’ (in terms of not having Eurasian admixture) allele frequencies (see SI) and calculated Wright’s FST, which showed that an ‘unadmixed’ Nubian gene-pool is genetically similar to Nilotes (S7B Fig). The strongest signal of admixture into Nubian populations came from Eurasian populations (S10 Fig, S2 Table) and was likely quite extensive: 39.41%-47.73% (f4-ratio, Z-scores between 22.8 and 26.7 Fig 3B, S9 Fig). Interestingly, the Nubians showed the highest level of allelic richness, number of private alleles and shared private alleles (ADZE, between Danagla and Halfawieen, S12 Fig) among all Sudanese and South Sudanese groups. This observation together with a smaller total length of runs of homozygosity, between lengths of 0.5–1 kilobases, points to substantial admixture in Nubians (Fig 4). Hence, the Nubians can be seen as a group with substantial genetic material relating to Nilotes that later have received much gene-flow from Eurasians (likely Middle Eastern) and from East Africans (Fig 2). Fig 4. Distribution of total length of runs of homozygosity per individual per population. Assuming that the Nubian population is a mixture of an incoming Eurasian (TSI is used as a proxy) group and a resident group that is genetically similar to the current day Nilotes (Nuer is used as a proxy), first contact is dated using patterns of LD-decay [34] to roughly 56 generations ago for the Danagla (54.45 +/- 10.34, Z = 5.26437) and the Mahas (58.35 +/- 12.2, Z = 4.78402); the Halfawieen have received Eurasian admixture later, around 19 generations ago (19.31 +/- 3.81, Z = 5.05949, S7 Table, Fig 3C). Assuming a generation time of 30 years, the admixture dates for Danagla and Mahas predate the Arab expansion in the 7th century, and may suggest that the migrations and admixture predate Islamic conquest. However, the confidence intervals overlap with the 7th century, and these admixture estimates largely coincide with the Arab expansion into the northeast of Sudan. It is known from historic sources that Arabic groups encountered the Nubians first in the 7th century, and were held back from advancing further into the Sahel until the fall of Dongola in 1315/1316AD [36] and the collapse of the Kingdom of Makuria. This is consistent with the later date for the admixture into Halfawieen and the Arabic populations of Sudan. Previous studies [37, 38] have found a similar pattern for populations of Maghreb, where admixture times coincide with the time of the historically documented Arab conquest. The Eurasian migrations also appear to have expanded and migrated into northeast Africa where they admixed with local populations giving rise to Arabic-speaking groups (Shaigia, Gaalien and Bataheen) that today inhabit areas of central Sudan (Fig 2). We further tested the source of admixture into the central Sudan Semitic speaking Arab groups (Shaigia, Gaalien and Bataheen) using ancient samples from Europe (LBK) and East Africa (Mota) and the population history of D(Ju|’hoansi,LBK;Mota,X), (where the Ju|’hoansi is an outgroup Khoe-San population from Namibia), which suggested Eurasian admixture into central Sudan Arab groups (see SI, S8A Fig). This migration and admixture occurred later than the events that brought Eurasian gene-flow into the Nubians (S3 Table, Fig 3C). Interestingly, when we overlay the Eurasian genetic component onto a geographic map, it appears as if the expansion could have spread along the Blue Nile (Fig 3B and 3C), showing a gradient of higher to lower admixture proportion and older to younger admixture dates from northern Sudan to South Sudan. The Eurasian admixture proportion in the Arab populations is high, ranging between ~40%–48% (SI, Fig 3B and S9A Fig). The presence of a northeast African genetic signature similar to Nilotic populations and the recent admixture signal from Eurasia indicates that the populations in central Sudan that self-identify as Arab were originally a local northeast African population (similar to the Nubians and the Beja) that mixed with a Eurasian population during the Arab expansion, or possibly earlier. However, the mixed groups kept the language and culture of the incoming migrants. Beja groups, who generally reside in eastern areas of Sudan close to the sea, show high non-African admixture in all tests (Figs 2 and 3B, S1–S6 and S8–S10 Figs). The Beni Amer also showed a strong admixture signal with a Eurasian population as well as a shared ancestry component with the Somali population (pink component in Fig 2), which suggest admixture with the East African Cushitic-speaking populations, perhaps as a result of migration along the coast. We dated the admixture of the Beja populations with the Cushitic-speaking Somalian population [39], and the admixture dates go far back in time, about 59 generations ago for the Hadendowa and about 68–75 generations for the Beni Amer (S3 and S4 Tables). The large proportion of the East African (pink in Fig 2) component is therefore not a result of recent admixture of East Africans into the Beni Amer. Admixture of non-Africans into the Beni Amer was also dated to an early event about 107.7+/-24.4 generations ago (Z = 4.41711) and a younger event, 34.2 generations ago (+/- 9.6, Z-score = 3.55532 Fig 3C, S7 Table) suggesting an early migration from Eurasian into these coastal African populations, possibly across the sea. However, these old admixture events into the Beni Amer could be driven by admixture from the Cushitic-speaking populations of the Horn of Africa, which themselves have received 30–50% non-African ancestry about 100 generations ago, or 3kya [22, 40]. Hollfelder N, Schlebusch CM, Günther T, Babiker H, Hassan HY, Jakobsson M (2017) Northeast African genomic variation shaped by the continuity of indigenous groups and Eurasian migrations. PLoS Genet 13(8): e1006976.
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Post by Admin on Oct 11, 2017 19:01:49 GMT
African genetic diversity is still incompletely understood, and vast regions in Africa remain genetically undocumented. Chad, for example, makes up ∼5% of Africa’s surface area, and its central location, connecting sub-Saharan Africa with North and East Africa, positions it to play an important role as a crossroad or barrier to human migrations. However, Chad has been little studied at a whole-genome level, and its position within African genetic diversity is not well known. With 200 ethnic groups and more than 120 indigenous languages and dialects, Chad has extensive ethnolinguistic diversity.1 It has been suggested that this diversity can be attributed to Lake Chad, which has attracted human populations to its fertile surroundings since prehistoric times, especially after the progressive desiccation of the Sahara starting ∼7,000 years ago (ya).2,3 Important questions about Africa’s ethnic diversity are the relationships among the different groups and the relationships between cultural groups and existing genetic structures. In the present study, we analyzed four Chadian populations with different ethnicities, languages, and modes of subsistence. Our samples are likely to capture recent genetic signals of migration and mixing and also have the potential to show ancestral genomic relationships that are shared among Chadians and other populations. An additional major question relates to the prehistoric Eurasian migrations to Africa: what was the extent of these migrations, how have they affected African genetic diversity, and what present-day populations harbor genetic signals from the ancient migrating Eurasians? We have previously reported evidence of gene flow from the Near East to East Africa ∼3,000 ya, as well as subsequent selection in Ethiopians on non-African-derived alleles related to light skin pigmentation.4 A recent attempt to quantify the extent of such backflow into Africa more generally, by using ancient DNA (aDNA), suggested that the impact of the Eurasian migration was mostly limited to East Africa.5 However, previous studies using mitochondrial DNA and the Y chromosome in populations from the Chad Basin found some with an East African6 or Mediterranean and Eurasian influence,7,8 and analysis based on genome-wide data9 found a non-African component (suggested to be from East Africa) in central Sahelian populations. Thus, studying diverse Chadian populations on a whole-genome level presents an opportunity to shed more light on the history of African-Eurasian mixtures, including whether or not selection after admixture is a widespread phenomenon in Africa and how the historical events in Chad are related to events that have occurred elsewhere in Africa and the Near East. Figure 1. Population Locations and Genetic Structure Genetic Structure in Chad Indicates a Complex Admixture History We performed an initial exploration of our dataset by using principal-component analysis (PCA).19 The first component (PC1) captured the genetic differentiation between Africans and Eurasians (Figure 1B). Populations such as the Near Easterners and North and East Africans fell between the Europeans and sub-Saharan Africans. The Chadian groups lay near the sub-Saharan Africans: the Sara and Laal speakers clustered tightly with sub-Saharan Africans, such as the Yoruba, whereas the Toubou were somewhat more distant and appeared drawn toward East Africans, such as the Ethiopians. Samples collected from the capital of Chad, N’Djamena, appeared in a central position between the Toubou cluster and the Sara and Laal cluster (Figure 1C). Many individuals from N’Djamena have not reported their ethnicity or have reported a mixed ethnic origin. Therefore, recent mixture could be responsible for their position on the PCA. We further investigated the genetic variation in Chad by estimating changes in the effective populations size (Ne) over time via the MSMC approach.20 Eurasians and Africans diverged around 60,000–80,000 ya and subsequently had different patterns of population-size changes: in particular, compared with Africans, the Eurasian population experienced a sharp decrease in size ∼60,000 ya.20 We observed this expected pattern in most populations in our dataset (Figure 2), but a few stood out: (1) Egyptians had a population bottleneck that was much more pronounced than that of other Africans but not as sharp as that of Eurasian populations; and (2) the Toubou and Ethiopians shared a very similar pattern during the bottleneck: they were close to other Africans but had a somewhat sharper decrease in population size (Figure 2). We would not expect such different fluctuations in population sizes at 60,000 ya in populations who shared a common origin during this period. For example, all Eurasians trace their origin to a population who exited Africa ∼60,000 ya, and this is reflected in indistinguishable Ne patterns during this period,20,33 which we also observed in the CEU, Greeks, and Lebanese (Figure 2), as expected. A shared pattern of Ne in ancient times was also observed in the Sara, Laal speakers, and other Africans, such as the Yoruba. We suggest that the deviation from the expected Ne pattern in the Toubou is related to extensive admixture history with Eurasians, like the Eurasian admixture seen in Ethiopians, and we explore this possibility directly with admixture tests below.
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Post by Admin on Oct 12, 2017 19:07:43 GMT
Figure 2. Population-Size Estimates from Whole-Genome Sequences Multiple Eurasian Admixtures in Africa after 6,000 ya We have previously reported massive gene flow ∼3,000 ya from Eurasians to Ethiopian populations.4 Here, we reassess the presence of Eurasian ancestry in Africa by using f3 statistics25 in the form of f3(X; Eurasian, Yoruba), where a negative value with a Z score < −4 indicates that X is a mixture of Africans and Eurasians. We found, as expected, that most Ethiopians are a mixture of Africans and Eurasians. An exception is the Gumuz population, where f3(Gumuz; Eurasian, Yoruba) is always positive. The Gumuz language belongs to the Nilo-Saharan family, which could have isolated the Gumuz from the Afro-Asiatic-speaking Ethiopians. However, we found that the Toubou in Chad, who also speak a Nilo-Saharan language, are a mixture of Africans and Eurasians, making f3(Toubou; Eurasian, Yoruba) always significantly negative. This suggests that the impact of Eurasian migrations today extends beyond East Africa and the Afro-Asiatic-speaking populations. We did not detect significant (Z score < −4) Eurasian admixture in the Sara (Nilo-Saharan language family) or the Laal speakers (unclassified language) with the use of f3 statistics (lowest Z score for the Sara was >−2.9; for the Laal speakers, Z scores were all positive). However, this statistic loses sensitivity with small mixture proportions and post-admixture drift,27 so positive values from the f3 statistics do not necessarily reflect a complete absence of admixture. We thus further tested for admixture by using ALDER and MALDER, which assess admixture-induced linkage disequilibrium (LD) and can detect small mixture proportions from a substantially diverged reference possibly missed by the f3 statistic. ALDER detected admixture in the Toubou, Sara, and Laal speakers (Table S2). MALDER, which has the potential to determine whether or not the admixture LD in the population is best represented as the result of one or multiple mixtures, showed that two mixture events had occurred in the Toubou (Figure 3A; Table S3). The first event occurred 2,850–3,500 ya (Z score = 11), a time close to the date of mixture in East Africans 2,500–2,700 ya (Z score = 26). The second mixture event occurred much more recently at 170–260 ya (Z score = 5). In southern Chad, we detected mixture events that were more ancient than those in the north. Mixture occurred 3,900–4,800 ya (Z score = 10) in the Sara and 4,750–7,200 ya (Z score = 5) in the Laal speakers (Figure 3A). These time estimates overlap, and we interpret them as signals from the same admixture event, whose time in the distant past was estimated more reliably in the Laal speakers because they carry more Eurasian ancestry (1.25%–4.5%) than the Sara (0.3%–2%) (see estimates of admixture proportions below), even though the Sara have smaller standard errors because of their larger sample size. In particular, we suggest that the Eurasian mixture event in the Sara and Laal speakers is independent of the mixture event in East Africans and the Toubou for two reasons: (1) admixture LD showed that the events in southern Chad preceded the events in East Africa by 2,000–4,500 years, and (2) we found in Chad a Eurasian Y chromosome lineage (Y haplogroup R1b-V88) that had penetrated all Chadian populations examined but was absent or rare from the Ethiopians examined (Table S4; Figure S1). From whole Y chromosome sequences (Figure S2), we estimate that the Chadian R1b-V88 chromosomes sampled emerged 5,700–7,300 ya (Figure 3B), a time comparable to the Laal speaker admixture dates (4,750–7,200 ya) estimated from genome-wide LD-decay patterns. Figure 3. Timing of the Eurasian Admixture in Africa The Sources of Eurasian Backflow into Chad and East Africa Are Correlated Previous studies have suggested that the Eurasian backflow into East Africa came from a population related to early Neolithic farmers.5 We wanted to know whether the Eurasian ancestry we found in the Toubou, which we attribute to a mixture close in time to the date of mixture in East Africans, can be traced to the same source populations that influenced Ethiopia. We performed the tests f3(Toubou; Yoruba, X) and f3(Amhara; Yoruba, X), where X is a present-day non-sub-Saharan African population in our dataset and is related to one that contributed ancestry to the Toubou and Amhara (Z score < −4) (Table S5). We then looked at the correlation of the f3 statistic values between the two tests (Figure 4A). We found that the Eurasian source populations for the Amhara and Toubou were highly correlated (r = 0.98; 95% CI = 0.98–0.99; p value < 2.2 × 10−16) and that the most significant result was for present-day Sardinians. Exceptions to this correlation were the North African populations (Tunisians, Mozabite, Algerians, and Saharawi), who appeared to have contributed more ancestry to the Toubou than to the Amhara. We repeated the tests by using published ancient genomes (Table S6) and also found a high correlation of the Eurasian sources for the Amhara and Toubou (r = 0.98; 95% CI = 0.97–0.99; p value < 2.2 × 10−16); early Neolithic farmers were the most significant contributors, as reported previously5 (Figure 4B). When we substituted the Amhara with other Ethiopians (Wolayta and Oromo), we found similar results (data not shown). In a parallel comparison, we checked whether the sources of the African ancestry in different Near Eastern populations were also correlated. We tested f3(Lebanese; British, X) and f3(Yemeni; British, X) and found a lower correlation of the f3 values (r = 0.62; 95% CI = 0.32–0.80), suggesting a more complicated history of gene flow from genetically different Africans to different populations in the Near East.
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Post by Admin on Oct 13, 2017 18:44:42 GMT
Figure 4. Sources of the Eurasian Ancestry in Chad and Ethiopia We next quantified the proportion of African-Eurasian mixture in the study populations by using two methods: (1) ADMIXTURE26 supervised with K = 2 and the British and Yoruba as ancestral populations and (2) the f4 ratio α = f4(British, chimp; X, Yoruba)/f4(British, chimp; early Neolithic farmer, Yoruba), where X is one of the populations in our dataset (Figure S3). The results from the two tests were highly correlated (r = 0.998; 95% CI = 0.996–0.999; p value < 2.2 × 10−16). Eurasian ancestry was estimated at 26%–30% in the Toubou, 0.3%–2% in the Sara, and 1.2%–4.5% in the Laal speakers. Eurasian ancestry in Ethiopians ranged from 11%–12% in the Gumuz to 53%–57% in the Amhara. African ancestry in the Near East ranged from 7%–14% (Yemen) to 0.7%–5% (Lebanese Christians). Eurasian Gene Flow Shaped the Genomes of Admixed Africans Our results from the PCA and MSMC analysis showed a deviation of the admixed populations from the patterns observed in unadmixed (or less admixed) populations in the same geographical region. The MSMC analysis, in particular, showed that admixed Africans had patterns indicative of a decline in heterozygosity (increased bottleneck ∼60,000 ya), somewhat similarly to Eurasians. We tested whole-genome heterozygosity in these populations and found that it decreased in admixed Africans according to their Eurasian ancestry (Figure S4A). This decrease was not related to recent inbreeding, given that removing segments with long runs of homozygosity did not change the overall pattern. Our simulations suggest that decay in heterozygosity is expected after gene flow from a population with diversity comparable to that of Eurasians (Figures S4B and S4C). We further investigated heterozygosity in admixed Africans by assessing heterozygosity of the different ancestral segments in the Toubou genome. We found that admixed African-Eurasian segments had more heterozygosity (1.23 hets/kb) than segments of the genome where African-African haplotypes were present (1.19 hets/kb) (Figure S5). However, the Toubou genome segments with complete Eurasian ancestry (Eurasian-Eurasian) had considerably lower heterozygosity (∼0.96 hets/kb; Figure S5), leading to the genome-wide pattern of decay in heterozygosity observed in Africans with Eurasian ancestry (Figure S4). We wanted to understand the consequence of admixture on the models that use the density of heterozygous sites to infer the demographic history of populations. We first tested whether the coalescent history estimated by MSMC was affected by a small proportion of mixture, such as the African mixture found in Greeks and Lebanese (ranging from 0% to 5%). We tested the Greek, Lebanese, CEU, and CHB (Han Chinese in Beijing, China) split times from the Yoruba and found that all populations split from the Yoruba ∼70,000–80,000 ya, implying that the low proportions of African admixture in the Greeks and Lebanese did not detectably affect the estimates of relative cross-coalescence rate (Figure S6A). We next tested the Toubou, who have ∼30% Eurasian ancestry. The Toubou appeared to split from Eurasians ∼30,000–40,000 ya, a time more recent than expected considering the African-Eurasian split 60,000–80,000 ya20 (Figure S6B). We tested other Africans in our dataset and found that the Sara, Laal speakers, and Yoruba split from Eurasians, as expected, ∼70,000–80,000 ya (Figure S6B). We then tested directly whether the Eurasian ancestry affected the relative cross-coalescence rate between the Toubou and Eurasians by masking some of the Eurasian ancestry in the Toubou. We used PCAdmix21 to estimate the ancestry along each chromosome and then used the identified Eurasian segments as a negative mask in our analysis. The split times between the Toubou and Lebanese, for example, increased by ∼15,000 years (Figure S6B), shifting the split date toward the expected African-Eurasian split time. Figure 5. Neanderthal Ancestry Correlation with the African-Eurasian Admixture We then computed the correlation between the Neanderthal ancestry proportions and the Eurasian and African ancestry proportions we identified. Neanderthal ancestry in admixed Africans and Near Easterners was highly correlated with their Eurasian ancestry (r = 0.98; p value < 2.2 × 10−16) and inversely correlated with their African ancestry (Figure 5). We detected the earliest Eurasian migrations to Africa in the Laal-speaking people, an isolated language group of fewer than 800 speakers who inhabit southern Chad. We estimate that mixture occurred 4,750–7,200 ya, thus after the Neolithic transition in the Near East, a period characterized by exponential growth in human population size. Environmental changes during this period (which possibly triggered the Neolithic transition) also facilitated human migrations. The African Humid Period, for example, was a humid phase across North Africa that peaked 6,000–9,000 ya37 and biogeographically connected Africa to Eurasia, facilitating human movement across these regions.38 In Chad, we found a Y chromosome lineage (R1b-V88) that we estimate emerged during the same period 5,700–7,300 ya (Figure 3B). The closest related Y chromosome groups today are widespread in Eurasia and have been previously associated with human expansions to Europe.39,40 We estimate that the Eurasian R1b lineages initially diverged 7,300–9,400 ya, at the time of the Neolithic expansions. However, we found that the African and Eurasian R1b lineages diverged 17,900–23,000 ya, suggesting that genetic structure was already established between the groups who expanded to Europe and Africa. R1b-V88 was previously found in Central and West Africa and was associated with a mid-Holocene migration of Afro-asiatic speakers through the central Sahara into the Lake Chad Basin.8 In the populations we examined, we found R1b in the Toubou and Sara, who speak Nilo-Saharan languages, and also in the Laal people, who speak an unclassified language. This suggests that R1b penetrated Africa independently of the Afro-asiatic language spread or passed to other groups through admixture. In addition to the early Eurasian migration to Africa ∼6,000 ya, a second migration ∼3,000 ya affected the Toubou population in northern Chad but had no detectable genetic impact on other Chadian populations. This migration appears to be associated with the previously reported Eurasian backflow into East Africa, given that the source populations and dates of mixture are similar. Occurring at the start of the Iron Age, these migrations could have been facilitated by advances in warfare and transportation technology in the Near East. It is uncertain why the impact of this migration in Chad affected only the Toubou. The African ancestral component in the Toubou is best represented by the Laal-speaking population, suggesting that the African-Eurasian mixture probably occurred in Chad. However, ethnolinguistic barriers could have already been established at this time between the Chad groups, preventing a widespread dissemination of the Eurasian ancestry. The Toubou, despite their Islamic faith, do not show the genetic admixture detected in many Near Eastern and North African populations around 1,100 ya,41 suggesting conversion without population mixing at this time. They did, however, receive additional Eurasian ancestry in the past 200 years from a source represented by North African populations such as Tunisians, Mozabite, Algerians, and Sahrawi (Figure 3C). This recent interaction could have been promoted by the nomadic lifestyle of the present-day Toubou and a shared Muslim religion with North Africans. Unsurprisingly, we also detected a likely mixing of Chad populations in the sample from the capital, which could be even more recent. Eurasian backflow into Africa thus appears to have been a recurrent event in the history of many Africans, given its considerable impact on their genomes. Although population mixture in general is a process that increases genetic diversity, we observed a decrease in heterozygosity in the admixed Africans. Our simulations showed that these results are expected after mixture at these proportions with the Eurasians who suffered a significant bottleneck at the time of their exodus from Africa ∼60,000 ya. Consequently, we found that mixture can complicate interpretation of the coalescent history inferred from models that use the density of heterozygous sites in their implementations. In addition, we detected in admixed Africans an inflation of positive-selection signals on alleles associated with adult lactose tolerance and pigmentation in Europeans, but we suggest that these alleles have drifted neutrally in Africans after admixture. Furthermore, we detected Neanderthal ancestry in admixed Africans and found it to be proportional to their Eurasian ancestry. Similarly, in admixed Near Easterners, we found a decrease in Neanderthal ancestry proportional to the gene flow they have received from Africans. Although a higher genetic affinity of Neanderthals to Europeans than to Near Easterners was previously interpreted as additional Neanderthal admixture in the history of Europeans,42 we propose that a more parsimonious explanation for these observations is that African-Eurasian mixtures both introduced Neanderthal ancestry to Africa and “diluted” the Neanderthal ancestry in the Near East. The American Journal of Human Genetics Volume 99, Issue 6, 1 December 2016, Pages 1316-1324
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Post by Admin on Dec 14, 2017 18:50:36 GMT
New archaeological evidence has undermined elements of the so-called "Out of Africa" theory, the widely supported model that maps the migration of the earliest humans from Africa. Scientists now believe humans departed Africa as early as 120,000 years ago—60,000 years earlier than previously thought. Researchers from the Max Planck Institute for the Science of Human History, in Jena, Germany, and the University of Hawaii at Manoa, used cutting-edge DNA analysis to date ancient human bones found in Asia. In a report published in the journal Science on Thursday, the researchers reveal that the bones, from southern and central China, date from between 70,000 and 120,000 years ago. Other recent studies link DNA from all contemporary non-African populations to the "Out of Africa" migration event. Scientists believe that vast numbers of prehistoric humans left the continent in one enormous departure 60,000 years ago. The new research proposes a new model for early human migration, which builds on the existing theory. Long before the giant migration, small pockets of explorers traveled the world. In a press release, anthropologist Michael Petraglia, from the research team, said: "The initial dispersals out of Africa prior to 60,000 years ago were likely by small groups of foragers, and at least some of these early dispersals left low-level genetic traces in modern human populations." First to set foot on modern-day Asian soil, these pioneers traveled as far as Australia. Not only did they discover much of today’s world, but they got friendly with our non-human cousins.
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