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Post by Admin on Apr 23, 2022 20:27:11 GMT
GENOMIC DATA AND THE STATUS OF HEIDELBERGENSIS As I previously argued,32 reclassifying the SH material as an early form of H. neanderthalensis on the basis of its derived Neanderthal features and dating it to no earlier than 400 ka would remove most of the data supporting a European chronospecies of H. heidelbergensis-H. neanderthalensis. This would open the possibility of a less inclusive diagnosis for the species that is ancestral to modern humans and Neanderthals, which, in my view, is still most reasonably named Homoheidelbergensis. However, new data on the possible eastern representatives of heidelbergensis have emerged from the genomic study of fragmentary fossils at the southern Siberian site of Denisova. Initial mitochondrial DNA (mtDNA) study of a large molar suggested an ancient lineage predating the divergence of Neanderthals and modern humans, but genomic reconstruction centered on a phalanx indicated that the “Denisovans” were actually a subgroup of the Neanderthal clade.47 This finding has fueled speculation that fossils previously considered to be possible Asian representatives of heidelbergensis, such as Dali, Jinniushan, and Narmada,13 could in fact be Denisovans, but this will remain uncertain until more complete material yields DNA. More ancient Asian specimens such as the Yunxian crania (China) might still represent examples of heidelbergensis13, 43 and potential ancestors of the Denisovans, although biogeographic and archeological arguments can be made against such as assignment.44 In addition, the presence of relatives of the Neanderthals in the Far East forcefully reminds us how much our views are biased by the attention paid to the European and African records. We cannot exclude an Asian origin for heidelbergensis, given the similar ages (∼600 ka) assigned to the earliest (if we exclude Tighenif) potential examples in Germany (Mauer22), China (Yunxian45), and Ethiopia (Bodo46). The new Denisovan genomic data are also consistent with previous evidence of gene flow between Homosapiens dispersing from Africa and native archaic populations (Neanderthals).33 Limited but viable hybridization events led to an input of “archaic” genes into all non-African people in the case of Neanderthal DNA, and Australasian populations in the case of the Denisovans.47 Such gene flow is bound to raise serious issues about the validity of specific distinctions between heidelbergensis and its daughter species, particularly as such hybridization events may even have occurred in Africa.48, 58 Nevertheless, on morphological grounds, I believe that a pragmatic case can still be made for such species distinctions, especially bearing in mind the extensive evidence for interspecific hybridization even in living primates.49 Genetic data can provide new perspectives on the evolutionary history of heidelbergensis and its daughter species, as can be illustrated by comparing Figure 1c and Figure 3, based on the mtDNA divergence data discussed earlier. Gene trees are not species trees, of course, but Figure 3 may nonetheless serve as a useful heuristic device. First, it is evident that both the modern human (A) and late Neanderthal lineages (B) may have suffered bottlenecking, perhaps during the harsh conditions of Marine Isotope Stage (MIS) 6; the slender evidence of Denisovan mtDNA already suggests greater diversity in that lineage.50 Genetic diversity that would have been represented within early or archaic members of the sapiens (C) and neanderthalensis groups (D) has consequently been lost. The hypothetical mtDNA last common ancestor for A+C and B+D is estimated at 338-538 ka (mean 407 ka), while population divergence is placed at 315-506 ka (mean 345 ka). The predivergence segment labeled F would have existed during the time span of Homo heidelbergensis. I argue that if we had fossils of the relevant ancestors, we would recognize them as members of that species. While fossils such as Swanscombe and SH might correspond with segments D or E, in my view we have yet to identify specimens showing convincing apomorphies of Homo sapiens that could represent the earliest stages of segment C, although fossils such as those from Florisbad and Guomde are possible candidates. Figure 2 Facial (A) and lateral (B) views of crania. Clockwise from top left: Homo erectus (replica, Sangiran, Java), heidelbergensis (Broken Hill, Zambia), sapiens (recent, Indonesia), and neanderthalensis (replica, La Ferrassie, France). All pictures © The Natural Histroy Museum London.
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Post by Admin on Apr 23, 2022 21:22:13 GMT
Figure 3 Reconstruction of mtDNA evolution in the sapiens and neanderthalensis lineages, based on complete genomes from 5 Neanderthals and 54 modern humans. Based on data in Endicott, Ho, and Stringer.32 As for what initiated the divergence of these lineages, one possibility is to return to an idea suggested more than 50 years ago by Howell,51, 52 though framed by him in the context of the last glaciations. There is evidence now that glaciation in the Balkans was much more severe during the Middle Pleistocene than at the Last Glacial Maximum.53 Also, pollen data from Tenaghi Philippon indicate that MIS 12 (∼450 ka) was particularly severe.54 If, at that time, cold, arid conditions extended eastward across the high relief of the Taurus-Zagros mountain systems, coupled with enlarged Caspian and Black Seas, European populations could have been effectively isolated from their African and Asian counterparts. Moreover, increased aridity in North Africa and the Levant could have added to this paleogeographic separation. Whether increased selection or drift then operated to differentiate these separated populations progressively is still uncertain,55 but Neanderthal-derived features are evident in Europe from MIS 11 onward.13, 52, 56 A comparable speciation scenario, using the mechanisms of refugia, has recently been proposed by Stewart and Stringer57: “When a lineage adopts a new (or changes its) refugial area, and it survives for a number of Milankovitch cycles, expanding from and contracting into that new refugium instead of its original refugium, it is destined to evolve into a distinct population. Given enough time in isolation, it will become a new species…. A new refugium is unlikely to have the same flora, fauna, and ecology compared to the lineage's original refugium, which contributes selective pressure to adapt and diverge.” CONCLUDING REMARKS Clearly, many problems in Middle Pleistocene human evolution remain unresolved. Some of these center on chronological issues, others on the lack of data for some important fossils, such as those from China. The relationship of Homo antecessor, still definitely identified only from Atapuerca, to succeeding samples is also unclear, although it remains possible that this derivative of Homo erectus went extinct during the early Middle Pleistocene.59Homo antecessor also seems an unlikely ancestor for Homo heidelbergensis, which means that the origin of Homo heidelbergensis is obscure. However, in my view, the main uncertainty about Homo heidelbergensis is much more fundamental, concerned with its very nature. The idiosyncratic morphology of the type specimen is certainly problematic, but for me an even more vexing issue is whether the species existed only in western Eurasia and gave rise solely to the Neanderthals. The main support for such a view has come from the derived Neanderthal features claimed for the species, simultaneously differentiating it from contemporaneous African fossils and linking it to the succeeding Neanderthals. In this review, I have discussed the growing and, in my view, convincing evidence that the Sima de los Huesos material belongs to the Neanderthal clade, and perhaps represents a primitive form of Homo neanderthalensis. Removing the extensive SH assemblage from H. heidelbergensis greatly clarifies the situation in also removing most of the unique links to the Neanderthals. This allows a reformulated heidelbergensis to approximate more closely the plesiomorphous morphotype expected for the last common ancestor of Homo neanderthalensis and Homo sapiens. However, if genetic and morphological estimates for neanderthalensis-sapiens divergence at <530 ka are accurate, the SH material must be younger, and perhaps considerably younger, than this date. The addition of “Denisovans” to the hominin lexicon provides a further dimension to these discussions. The relationship of non-erectus Asian Middle Pleistocene fossils to those further west has long been problematic, but now we have the potential to properly integrate the hominin records from western and eastern Eurasia for the first time, and to see East Asian fossils like Dali and Jinniushan as counterparts of the evolving Neanderthals further west. Indeed, it may be just as logical to regard the Neanderthals as a western subset of the Denisovan group as to consider, as is usually done, the inverse relationship. The concept of Homo heidelbergensis remains at the center of such discussions, as this species represents the probable ultimate ancestor of these three daughter allotaxa: sapiens, neanderthalensis, and Denisovans. Acknowledgements I thank numerous colleagues, including those quoted here, for discussions about Homo heidelbergensis, and four reviewers for their helpful comments. I also thank Laura Buck for her work on the manuscript and figures. Figure 1 was redrawn with permission from Elsevier. The original version of Figure 3 was kindly supplied by Phillip Endicott. My work forms part of the Ancient Human Occupation of Britain project, funded by the Leverhulme Trust, and is supported by the Human Origins Research Fund, and the Calleva Foundation.
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Post by Admin on May 9, 2022 17:18:59 GMT
Aspects of human physical and behavioural evolution during the last 1 million years Julia Galway-Witham,James Cole,Chris Stringer First published: 14 August 2019 doi.org/10.1002/jqs.3137ABSTRACT This paper reviews some of the main advances in our understanding of human evolution over the last 1 million years, presenting a holistic overview of a field defined by interdisciplinary approaches to studying the origins of our species. We begin by briefly summarizing the climatic context across the Old World for the last 1 million years before directly addressing the fossil and archaeological records. The main themes in this work explore (i) recent discoveries in the fossil record over the last 15 years, such as Homo naledi and Homo floresiensis; (ii) the implications of palaeogenetics for understanding the evolutionary history of, and relationships between, Neanderthals, Denisovans and Homo sapiens; (iii) the interplay between physiology and metabolic demand, landscape use, and behavioural adaptations in the evolution of morphological and behavioural innovation; and (iv) recent advances in archaeological understanding for the behavioural record, in particular that of the Neanderthals. This paper seeks to provide a broad-scale, holistic perspective of our current understanding of human evolution for the last 1 Ma, providing a reference point for researchers that can be built upon as new discoveries continue to develop the landscapes of human evolution. © 2019 The Authors. Journal of Quaternary Science Published by Wiley Periodicals, Inc. 1 Introduction At the beginning of this century, the basic pattern of human evolution in the Old World over the last 500 000 years seemed relatively clear for the researchers who accepted that our species, Homo sapiens, had a recent African origin. The archaic species Homo heidelbergensis was widespread, then splitting into two descendant lineages about 400 ka, before subsequently disappearing from the fossil record. ‘Archaic’ is a descriptive term used here to indicate most members of the genus Homo and their common traits, such as a long, low braincase, and strong continuous browridge. Contrasted with H. sapiens and its ‘modern’ traits, such as a globular braincase, lack of a browridge, a chin and a narrow pelvis. Those descendants gradually evolved into Homo neanderthalensis in western Eurasia, and H. sapiens in Africa (Stringer, 2002). The oldest recognizable members of the descendant lineages were perhaps the Swanscombe skull (UK, about 400 ka – a possible Neanderthal ancestor) and the Omo Kibish 1 skeleton (Ethiopia, then estimated age > 130 ka – an early H. sapiens) (Stringer, 2002). Genetic data from extant humans suggested that H. sapiens had dispersed from Africa about 55 ka, reached Australia by about 45 ka, and by 30 ka had replaced the Neanderthals across Eurasia with minimal or no interbreeding (Hudjashov et al., 2007; Oppenheimer, 2009; Soares et al., 2009). Archaic populations of uncertain affinities existed in China, represented by fossils such as Dali and Maba, with unknown last appearance dates, while Homo erectus possibly persisted in Java (Indonesia) until about 45 ka, roughly coincident with the spread of H. sapiens in the region (Stringer, 2002). In terms of range, it was thought that only H. sapiens, using ocean-going watercraft, had the capacity to spread eastwards beyond the biogeographical barrier in Southeast Asia known as the Wallace Line (Stringer, 2002). The last 40 years have seen the rise of numerous theories about the physical requirements for hominins to disperse into Europe and Asia (e.g. Klein, 2009), and the characteristic morphologies of Neanderthals and H. sapiens were primarily summarized as adaptations to the environments in which they evolved, with each species being either cold- or heat-adapted, respectively (e.g. Trinkaus, 1981). While the pattern of physical evolution seemed comparatively straightforward until the early 2000s, there was much debate on the topic of human behavioural complexity. The epitome of early arguments was encapsulated within the human revolution model (Mellars and Stringer, 1989), which saw a sudden appearance of modern human behavioural packages in Europe from ~40 ka, directly corresponding to the arrival of H. sapiens in the region. Within the last 15 years, the discovery of multiple new hominin taxa, as well as new studies of known taxa, have changed the landscape of palaeoanthropological research (Galway-Witham and Stringer, 2018), and signal how much we have yet to understand about human evolution during the last 1 million years. It is becoming increasingly evident that for every adaptive morphology, there are several potential adaptive pathways (Churchill, 2006), and while the development of energetic proxies, through analyses of body form, climate and behavioural indicators, are helping to tease apart these potential causes, relating form and function continues to be difficult. However, the discovery of new fossil sites in unexpected locations and time periods is encouraging us to look more closely at our implicit assumptions. In 2000, McBrearty and Brooks posed a counterposition to the human revolution model that put forward a gradual and much earlier assembling of the modern human behavioural package in Africa beginning ~300–250 ka. Such behaviours included blade and microlith technology, bone tools, increased geographical range, specialized hunting, the use of aquatic resources, long-distance trade, systematic processing and use of pigment, art and decoration (McBrearty and Brooks, 2000; also see Stringer, 2011, p. 115 for a refined list with useful examples). The next 7 years or so of research saw a healthy debate between these positions, culminating in an agenda-setting interdisciplinary rethink of the human revolution (Mellars et al., 2007), which started to suggest and acknowledge that the archaeological record was more complicated and surprising than had previously been recognized. Although it would need a book-length treatment to do justice to all the new data, the following review seeks to summarize some of the most striking new finds in palaeoanthropology and palaeolithic archaeology, bringing together the behavioural and physical evidence, and outlining some of the many remaining questions in understanding the last 1 million years of human evolution. Inevitably there are gaps in this review and we have tried to direct the reader to further resources where appropriate. We have chosen to highlight the complementary nature of the fossil and archaeological evidence by including a summary of new research relating to hominin energetics, sandwiched between the more explicit discussions of these preserved records. Figure 1 illustrates a hominin fossil timeline for the last 1 million years that will be followed through this paper. In addition, information on hominin cranial capacity and the timings of key behavioural traits are illustrated here. Figure 2 depicts what we consider to be the most probable phylogenetic associations between taxa, and Fig. 3 is a map of the Old World showing the location of sites mentioned in this paper.
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Post by Admin on May 9, 2022 18:52:41 GMT
Figure 1 Timeline illustrating key behavioural traits, hominin fossils and endocranial volume (data from S1) during the last million years. For the behavioural traits and fossils, the solid line represents more certain date ranges, while the segmented lines represent more ambiguous data points that extend beyond the range of established dates. The spacing of the horizontal segmented lines relates to the relative certainty of the associated dates. The fossil timeline does not include any phylogenetic inference. The coloured boxes represent endocranial volume ranges to illustrate areas of overlap in inferred brain size between taxa. Although we have used cited dates in relation to fossils, we do not necessarily agree with all of them.
Figure 2 Schematic diagram of the inferred age ranges of hominin lineages during the last million years. Colours reflect species designations as commonly referenced in the literature. For some species, there is potential for this taxon to encompass more than one ‘lineage’, e.g. H. erectus. Dotted lines indicate our conservative phylogenetic associations of lineages. (a) The evolutionary history of H. naledi remains particularly enigmatic, confounded by its unexpected combination of traits that makes it difficult to establish whether the species diverged early on in the evolution of the genus Homo, or split off from another lineage more recently. (b) The taxon designated H. sapiens may have evolved as a single lineage, where earlier specimens ~300 ka eventually evolved into the more derived specimens after 200 ka. However, the overlapping time periods of these evolving lineages presents an alternative evolution, where these earlier morphs represent a divergent sister lineage that perhaps did not contribute to the morphology of H. sapiens today. (c) Neanderthals also present two alternative evolutionary narratives; early Neanderthals could be the earlier members of the lineage that ultimately led to the classic Neanderthal morphology of the later Pleistocene, or it may represent a side branch of the lineage that diverged from the common ancestor with Denisovans. (d) The phylogenetic affinities of specimens designated here as ‘China archaics’ remains unspecified, until the phylogenetic status (i.e. derived versus ancestral) designation of traits shared with H. erectus, H. heidelbergensis, H. neanderthalensis and H. sapiens has been better established, and until we hopefully have a better idea of the morphology of the Denisovans. (e) H. floresiensis may be a descendant of H. erectus that dwarfed on the island of Flores, or alternatively it evolved from an even deeper, pre-erectus divergence. Here we remain agnostic, although the recently announced H. luzonensis (Détroit et al., 2019) may add to this debate. Evidence indicates that there was gene flow (red lines) at various times throughout the last 1 million years, although the rate and frequency of this is still being established.
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Post by Admin on May 9, 2022 21:58:54 GMT
Figure 3 (A) Map of Europe, Asia and Africa, with the sites mentioned within the text indicated. (B) Expanded view of Europe to show the distribution of sites therein. 2 Climatic context The potential impact of climate change on the development of evolutionary innovations and dispersals for hominins is well referenced and consistent with ecological theory (e.g. Gamble et al., 2004; James and Petraglia, 2005; Potts and Teague, 2010). Recent studies, however, have been looking at the more nuanced question of how and in what way climate may have changed, moving beyond the more traditional view that implicitly described a climate as either fixed or stable over a given period (Potts, 2013). In particular, this may involve an attempt to find longitudinal trends in temperature change (e.g. Petit et al., 1999; Lambert et al., 2008), aridity and precipitation (e.g. deMenocal, 1995, 2004, 2011), and overall climatic variability (e.g. Potts, 1996, 1998, 2012), and to correlate these trends with notable instances of evolutionary change (Potts, 2013; Shultz and Maslin, 2013; Grove, 2014; Maslin et al., 2014, 2015; Levin, 2015; Trauth et al., 2015; Carotenuto et al., 2016; Burke et al., 2017; Owen et al., 2018; Buck et al., 2018). Analyses of oxygen isotope data indicate that the Earth experienced an overall cooling over the last few million years, including within the last 1 million years (Sosdian and Rosenthal, 2009). Between ~1 Ma and 700 ka a period of extreme climatic variability appears to have coincided with the formation of large lakes in East Africa (Potts, 2013), and around this time (~940–870 ka) North Africa and eastern Europe were also subjected to increased aridification and climatic variability (Muttoni et al., 2010). This has led some authors to hypothesize about the potential role of climate change as a catalyst for the dispersal of large African mammals into southern Europe, including hominins (Muttoni et al., 2011; Abbate and Sagri, 2012). A similar period of potentially favourable climatic conditions has also been identified between 600 and 100 ka, and may have also permitted hominin dispersals out of Africa (Abbate and Sagri, 2012). The Early Pleistocene and Middle Pleistocene are separated by the Middle Pleistocene Transition (MPT), which occurred between ~922 and ~640 ka (Dennell et al., 2011). The Middle Pleistocene is characterized as a series of six ~ 100-ka periods of dominant or extreme cold in higher latitudes, punctuated by short periods of warmer interglacials (Dennell et al., 2011). Broadly, mild interglacial periods have been associated with indications of hominin habitation (Bermúdez de Castro and Martinón-Torres, 2013), and according to some researchers, the climate of south-west Asia throughout the Pleistocene may have been consistently suitable for hominin habitation (Hughes et al., 2007). Across the glacial/interglacial cycles, average aridity was generally increasing in the approach to the Last Glacial Maximum (26.5–~20 ka), and areas such as the Thar Desert would have been intermittently inhospitable (James and Petraglia, 2005). Equally, however, there were periods, notably 130–118, 106–94 and 89–73 ka (MIS 5) and 59–47 ka (MIS 3) when classically inhospitable areas such as the Sahara and the Arabian Desert were more highly vegetated due to increased monsoonal activity (deMenocal and Stringer, 2016). And within the larger orbitally controlled long-term climatic fluctuations there were also many short and sharp millennial-scale oscillations (Cohen and Gibbard, 2019). These are best known within the palaeoclimate records of the last 120 ka, and although still largely undetected, may also have been significant in controlling human population numbers and movements in earlier periods.
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