Extinct species of the genus Homo include Homo erectus, extant during roughly 1.9 to 0.4 million years ago, and a number of other species (by some authors considered subspecies of either H. sapiens or H. erectus). The age of speciation of H. sapiens out of ancestral H. erectus (or an intermediate species such as Homo antecessor) is estimated to have been roughly 350,000 years ago.[note 1] Sustained archaic admixture is known to have taken place both in Africa and (following the recent Out-Of-Africa expansion) in Eurasia, between about 100,000 and 30,000 years ago.
The species was initially thought to have emerged from a predecessor within the genus Homo around 300,000 to 200,000 years ago.[note 2] A problem with the morphological classification of "anatomically modern" was that it would not have included certain extant populations. For this reason, a lineage-based (cladistic) definition of H. sapiens has been suggested, in which H. sapiens would by definition refer to the modern human lineage following the split from the Neanderthal lineage. Such a cladistic definition would extend the age of H. sapiens to over 500,000 years.[note 3]
Extant human populations have historically been divided into subspecies, but since around the 1980s all extant groups have tended to be subsumed into a single species, H. sapiens, avoiding division into subspecies altogether.[note 4]
Some sources show Neanderthals (H. neanderthalensis) as a subspecies (H. sapiens neanderthalensis). Similarly, the discovered specimens of the H. rhodesiensis species have been classified by some as a subspecies (H. sapiens rhodesiensis), although it remains more common to treat these last two as separate species within the genus Homo rather than as subspecies within H. sapiens.
The subspecies name H. sapiens sapiens is sometimes used informally instead of "modern humans" or "anatomically modern humans". It has no formal authority associated with it.[note 5] By the early 2000s, it had become common to use H. s. sapiens for the ancestral population of all contemporary humans, and as such it is equivalent to the binomial H. sapiens in the more restrictive sense (considering H. neanderthalensis a separate species).[note 6]
Schematic representation of the emergence of H. sapiens from earlier species of Homo. The horizontal axis represents geographic location; the vertical axis represents time in millions of years ago (blue areas denote the presence of a certain species of Homo at a given time and place; late survival of robust australopithecines alongside Homo is indicated in purple). Based on Springer (2012), Homo heidelbergensis is shown as diverging into Neanderthals, Denisovans and H. sapiens. With the rapid expansion of H. sapiens after 60 kya, Neanderthals, Denisovans and unspecified archaic African hominins are shown as again subsumed into the H. sapiens lineage.
A model of the phylogeny of H. sapiens during the Middle Paleolithic. The horizontal axis represents geographic location; the vertical axis represents time in thousands of years ago.[note 1] Neanderthals, Denisovans and unspecified archaic African hominins are shown as admixed into the H. sapiens lineage. In addition, prehistoric Archaic Human and Eurasian admixture events in modern African populations are indicated.
The speciation of H. sapiens out of archaic human varieties derived from H. erectus is estimated as having taken place over 350,000 years ago, as the Khoisan split from other populations is dated between 260,000 and 350,000 years ago.
An alternative suggestion defines H. sapienscladistically as including the lineage of modern humans since the split from the lineage of Neanderthals, roughly 500,000 to 800,000 years ago.
The time of divergence between archaic H. sapiens and ancestors of Neanderthals and Denisovans caused by a genetic bottleneck of the latter was dated at 744,000 years ago, combined with repeated early admixture events and Denisovans diverging from Neanderthals 300 generations after their split from H. sapiens, as calculated by Rogers et al. (2017).
Since the 2000s, the availability of data from archaeogenetics and population genetics has led to the emergence of a much more detailed picture, intermediate between the two competing scenarios outlined above: The recent Out-of-Africa expansion accounts for the predominant part of modern human ancestry, while there were also significant admixture events with regional archaic humans.
Since the 1970s, the Omo remains, dated to some 195,000 years ago, have often been taken as the conventional cut-off point for the emergence of "anatomically modern humans". Since the 2000s, the discovery of older remains with comparable characteristics, and the discovery of ongoing hybridization between "modern" and "archaic" populations after the time of the Omo remains, have opened up a renewed debate on the age of H. sapiens in journalistic publications.H. s. idaltu, dated to 160,000 years ago, has been postulated as an extinct subspecies of H. sapiens in 2003.[better source needed]H. neanderthalensis, which became extinct about 40,000 years ago, has also been classified as a subspecies, H. s. neanderthalensis.
H. heidelbergensis, dated 600,000 to 300,000 years ago, has long been thought to be a likely candidate for the last common ancestor of the Neanderthal and modern human lineages. However, genetic evidence from the Sima de los Huesos fossils published in 2016 seems to suggest that H. heidelbergensis in its entirety should be included in the Neanderthal lineage, as "pre-Neanderthal" or "early Neanderthal", while the divergence time between the Neanderthal and modern lineages has been pushed back to before the emergence of H. heidelbergensis, to close to 800,000 years ago, the approximate time of disappearance of H. antecessor.
Many of the early modern human finds, like those of Omo, Herto, Skhul, Jebel Irhoud and Peștera cu Oase exhibit a mix of archaic and modern traits. Skhul V, for example, has prominent brow ridges and a projecting face. However, the brain case is quite rounded and distinct from that of the Neanderthals and is similar to the brain case of modern humans. It is uncertain whether the robust traits of some of the early modern humans like Skhul V reflects mixed ancestry or retention of older traits.
The "gracile" or lightly built skeleton of anatomically modern humans has been connected to a change in behavior, including increased cooperation and "resource transport".
There is evidence that the characteristic human brain development, especially the prefrontal cortex, was due to "an exceptional acceleration of metabolome evolution ... paralleled by a drastic reduction in muscle strength. The observed rapid metabolic changes in brain and muscle, together with the unique human cognitive skills and low muscle performance, might reflect parallel mechanisms in human evolution." The Schöningen spears and their correlation of finds are evidence that complex technological skills already existed 300,000 years ago, and are the first obvious proof of an active (big game) hunt. H. heidelbergensis already had intellectual and cognitive skills like anticipatory planning, thinking and acting that so far have only been attributed to modern man.
The ongoing admixture events within anatomically modern human populations make it difficult to estimate the age of the matrilinear and patrilinear most recent common ancestors of modern populations (Mitochondrial Eve and Y-chromosomal Adam). Estimates of the age of Y-chromosomal Adam have been pushed back significantly with the discovery of an ancient Y-chromosomal lineage in 2013, to likely beyond 300,000 years ago.[note 7] There have, however, been no reports of the survival of Y-chromosomal or mitochondrial DNA clearly deriving from archaic humans (which would push back the age of the most recent patrilinear or matrilinear ancestor beyond 500,000 years).
Overview map of the peopling of the world by anatomically modern humans (numbers indicate dates in thousands of years ago [ka])
Dispersal of early H. sapiens begins soon after its emergence, as evidenced by the North African Jebel Irhoud finds (dated to between 280,000 and 350,000 years ago). There is indirect evidence for modern human presence in West Asia around 270,000 years ago and Dali Man from China is dated at 260,000 years ago.
Among extant populations, the Khoi-San (or "Capoid") hunters-gatherers of Southern Africa may represent the human population with the earliest possible divergence within the group Homo sapiens sapiens. Their separation time has been estimated in a 2017 study to be as long as between 260,000 and 350,000 years ago, compatible with the estimated age of H. sapiens.H. s. idaltu, found at Middle Awash in Ethiopia, lived about 160,000 years ago, and H. sapiens lived at Omo Kibish in Ethiopia about 195,000 years ago. Fossil evidence for modern human presence in West Asia is ascertained for 177,000 years ago, and disputed fossil evidence suggests expansion as far as East Asia by 120,000 years ago.
In July 2019, anthropologists reported the discovery of 210,000 year old remains of a H. sapiens and 170,000 year old remains of a H. neanderthalensis in Apidima Cave, Peloponnese, Greece, more than 150,000 years older than previous H. sapiens finds in Europe.
A significant dispersal event, within Africa and to West Asia, is associated with the African megadroughts during MIS 5, beginning 130,000 years ago. A 2011 study located the origin of basal population of contemporary human populations at 130,000 years ago, with the Khoi-San representing an "ancestral population cluster" located in southwestern Africa (near the coastal border of Namibia and Angola).
Layer sequence at Ksar Akil in the Levantine corridor, and discovery of two fossils of Homo sapiens, dated to 40,800 to 39,200 years BP for "Egbert",and 42,400–41,700 BP for "Ethelruda".
Evidence for the overwhelming contribution of this "recent" (L3-derived) expansion to all non-African populations was established based on mitochondrial DNA, combined with evidence based on physical anthropology of archaic specimens, during the 1990s and 2000s.[note 9] The assumption of complete replacement has been revised in the 2010s with the discovery of admixture events (introgression) of populations of H. sapiens with populations of archaic humans over the period of between roughly 100,000 and 30,000 years ago, both in Eurasia and in Sub-Saharan Africa. Neanderthal admixture, in the range of 1-4%, is found in all modern populations outside of Africa, including in Europeans, Asians, Papuan New Guineans, Australian Aboriginals, and Native Americans. This suggests that interbreeding between Neanderthals and anatomically modern humans took place after the recent "out of Africa" migration, likely between 60,000 and 40,000 years ago. Recent admixture analyses have added to the complexity, finding that Eastern Neanderthals derive up to 2% of their ancestry from anatomically modern humans who left Africa some 100 kya. The extent of Neanderthal admixture (and introgression of genes acquired by admixture) varies significantly between contemporary racial groups, being absent in Africans, intermediate in Europeans and highest in East Asians. Certain genes related to UV-light adaptation introgressed from Neanderthals have been found to have been selected for in East Asians specifically from 45,000 years ago until around 5,000 years ago. The extent of archaic admixture is of the order of about 1% to 4% in Europeans and East Asians, and highest among Melanesians (Denisova hominin admixture), at 4% to 6%. Cumulatively, about 20% of the Neanderthal genome is estimated to remain present spread in contemporary populations.
Known archaeological remains of Anatomically Modern Humans in Europe and Africa, directly dated, calibrated carbon dates as of 2013.
Generally, modern humans are more lightly built (or more "gracile") than the more "robust" archaic humans. Nevertheless, contemporary humans exhibit high variability in many physiological traits, and may exhibit remarkable "robustness". There are still a number of physiological details which can be taken as reliably differentiating the physiology of Neanderthals vs. anatomically modern humans.
The term "anatomically modern humans" (AMH) is used with varying scope depending on context, to distinguish "anatomically modern" Homo sapiens from archaic humans such as Neanderthals and Middle and Lower Paleolithic hominins with transitional features intermediate between H. erectus, Neanderthals and early AMH called archaic Homo sapiens. In a convention popular in the 1990s, Neanderthals were classified as a subspecies of H. sapiens, as H. s. neanderthalensis, while AMH (or European early modern humans, EEMH) was taken to refer to "Cro-Magnon" or H. s. sapiens. Under this nomenclature (Neanderthals considered H. sapiens), the term "anatomically modern Homo sapiens" (AMHS) has also been used to refer to EEMH ("Cro-Magnons"). It has since become more common to designate Neanderthals as a separate species, H. neanderthalensis, so that AMH in the European context refers to H. sapiens (but the question is by no means resolved[note 10]).
In this more narrow definition of H. sapiens, the subspecies H. s. idaltu, discovered in 2003, also falls under the umbrella of "anatomically modern". The recognition of H. s. idaltu as a valid subspecies of the anatomically modern human lineage would justify the description of contemporary humans with the subspecies name H. s. sapiens.
A further division of AMH into "early" or "robust" vs. "post-glacial" or "gracile" subtypes has since been used for convenience. The emergence of "gracile AMH" is taken to reflect a process towards a smaller and more fine-boned skeleton beginning around 50,000–30,000 years ago.
The cranium lacks a pronounced occipital bun in the neck, a bulge that anchored considerable neck muscles in Neanderthals. Modern humans, even the earlier ones, generally have a larger fore-brain than the archaic people, so that the brain sits above rather than behind the eyes. This will usually (though not always) give a higher forehead, and reduced brow ridge. Early modern people and some living people do however have quite pronounced brow ridges, but they differ from those of archaic forms by having both a supraorbital foramen or notch, forming a groove through the ridge above each eye. This splits the ridge into a central part and two distal parts. In current humans, often only the central section of the ridge is preserved (if it is preserved at all). This contrasts with archaic humans, where the brow ridge is pronounced and unbroken.
Modern humans commonly have a steep, even vertical forehead whereas their predecessors had foreheads that sloped strongly backwards. According to Desmond Morris, the vertical forehead in humans plays an important role in human communication through eyebrow movements and forehead skin wrinkling.
Brain size in both Neanderthals and AMH is significantly larger on average (but overlapping in range) than brain size in H. erectus. Neanderthal and AMH brain sizes are in the same range, but there are differences in the relative sizes of individual brain areas, with significantly larger visual systems in Neanderthals than in AMH.[note 11]
Compared to archaic people, anatomically modern humans have smaller, differently shaped teeth. This results in a smaller, more receded dentary, making the rest of the jaw-line stand out, giving an often quite prominent chin. The central part of the mandible forming the chin carries a triangularly shaped area forming the apex of the chin called the mental trigon, not found in archaic humans. Particularly in living populations, the use of fire and tools requires fewer jaw muscles, giving slender, more gracile jaws. Compared to archaic people, modern humans have smaller, lower faces.
Body skeleton structure
The body skeletons of even the earliest and most robustly built modern humans were less robust than those of Neanderthals (and from what little we know from Denisovans), having essentially modern proportions. Particularly regarding the long bones of the limbs, the distal bones (the radius/ulna and tibia/fibula) are nearly the same size or slightly shorter than the proximal bones (the humerus and femur). In ancient people, particularly Neanderthals, the distal bones were shorter, usually thought to be an adaptation to cold climate. The same adaptation can be found in some modern people living in the polar regions.
Height ranges overlap between Neanderthals and AMH, with Neanderthal averages cited as 164 to 168 cm (65 to 66 in) and 152 to 156 cm (60 to 61 in) for males and females, respectively.[note 12] By comparison, contemporary national averages range between 158 to 184 cm (62 to 72 in) in males and 147 to 172 cm (58 to 68 in) in females. Neanderthal ranges approximate the height distribution measured among Malay people, for one.[note 13]
Physiological or phenotypical changes have been traced to Upper Paleolithic mutations, such as the East Asian variant of the EDAR gene, dated to c. 35,000 years ago.[note 15]
Recent divergence of Eurasian lineages was sped up significantly during the Last Glacial Maximum, the Mesolithic and the Neolithic, due to increased selection pressures and due to founder effects associated with migration. Alleles predictive of light skin have been found in Neanderthals, but the alleles for light skin in Europeans and East Asians, associated with KITLG and ASIP, are (as of 2012[update]) thought to have not been acquired by archaic admixture but recent mutations since the LGM. Phenotypes associated with the "white" or "Caucasian" populations of Western Eurasian stock emerge during the LGM, from about 19,000 years ago. Average cranial capacity in modern human populations varies in the range of 1,200 to 1,450 cm3 (adult male averages). Larger cranial volume is associated with climatic region, the largest averages being found in populations of Siberia and the Arctic.[note 16] Both Neanderthal and EEMH had somewhat larger cranial volumes on average than modern Europeans, suggesting the relaxation of selection pressures for larger brain volume after the end of the LGM.
An even more recent adaptation has been proposed for the Austronesian Sama-Bajau, developed under selection pressures associated with subsisting on freediving over the past thousand years or so.
Lithic Industries of early Homo sapiens at Blombos Cave (M3 phase, MIS 5), Southern Cape, South Africa (c. 105 – 90 Ka)
Bifacial silcrete point of early Homo sapiens, from M1 phase (71,000 BCE) layer of Blombos Cave, South Africa
The term "behavioral modernity" is somewhat disputed. It is most often used for the set of characteristics marking the Upper Paleolithic, but some scholars use "behavioral modernity" for the emergence of H. sapiens around 200,000 years ago, while others use the term for the rapid developments occurring around 50,000 years ago. It has been proposed that the emergence of behavioral modernity was a gradual process.
In January 2018, it was announced that modern human finds at Misliya cave, Israel, in 2002, had been dated to around 185,000 years ago, the earliest evidence of their out of Africa migration.
The equivalent of the Eurasian Upper Paleolithic in African archaeology is known as the Later Stone Age, also beginning roughly 40,000 years ago. While most clear evidence for behavioral modernity uncovered from the later 19th century was from Europe, such as the Venus figurines and other artefacts from the Aurignacian, more recent archaeological research has shown that all essential elements of the kind of material culture typical of contemporary San hunter-gatherers in Southern Africa was also present by least 40,000 years ago, including digging sticks of similar materials used today, ostrich egg shell beads, bone arrow heads with individual maker's marks etched and embedded with red ochre, and poison applicators. There is also a suggestion that "pressure flaking best explains the morphology of lithic artifacts recovered from the c. 75-ka Middle Stone Age levels at Blombos Cave, South Africa. The technique was used during the final shaping of Still Bay bifacial points made on heat‐treated silcrete." Both pressure flaking and heat treatment of materials were previously thought to have occurred much later in prehistory, and both indicate a behaviourally modern sophistication in the use of natural materials. Further reports of research on cave sites along the southern African coast indicate that "the debate as to when cultural and cognitive characteristics typical of modern humans first appeared" may be coming to an end, as "advanced technologies with elaborate chains of production" which "often demand high-fidelity transmission and thus language" have been found at Pinnacle Point Site 5–6. These have been dated to approximately 71,000 years ago. The researchers suggest that their research "shows that microlithic technology originated early in South Africa, evolved over a vast time span (c. 11,000 years), and was typically coupled to complex heat treatment that persisted for nearly 100,000 years. Advanced technologies in Africa were early and enduring; a small sample of excavated sites in Africa is the best explanation for any perceived 'flickering' pattern." These results suggest that Late Stone Age foragers in Sub-Saharan Africa had developed modern cognition and behaviour by at least 50,000 years ago. The change in behavior has been speculated to have been a consequence of an earlier climatic change to much drier and colder conditions between 135,000 and 75,000 years ago. This might have led to human groups who were seeking refuge from the inland droughts, expanded along the coastal marshes rich in shellfish and other resources. Since sea levels were low due to so much water tied up in glaciers, such marshlands would have occurred all along the southern coasts of Eurasia. The use of rafts and boats may well have facilitated exploration of offshore islands and travel along the coast, and eventually permitted expansion to New Guinea and then to Australia.
^ abBased on Schlebusch et al., "Southern African ancient genomes estimate modern human divergence to 350,000 to 260,000 years ago",Fig. 3 (H. sapiens divergence times) and Stringer (2012), (archaic admixture).
^This is a matter of convention (rather than a factual dispute), and there is no universal consensus on terminology. Some scholars include humans of up to 600,000 years ago under the same species. See Bryant (2003), p. 811. See also Tattersall (2012), Page 82 (cf. Unfortunately this consensus in principle hardly clarifies matters much in practice. For there is no agreement on what the 'qualities of a man' actually are," [...]).
^The history of claimed or proposed subspecies of H. sapiens is complicated and fraught with controversy. The only widely recognized archaic subspecies is H. sapiens idaltu (2003). The name H. s. sapiens is due to Linnaeus (1758), and refers by definition the subspecies of which Linnaeus himself is the type specimen. However, Linnaeus postulated four other extant subspecies, viz. H. s. afer, H. s. americanus, H. s. asiaticus and H. s. ferus for Africans, Americans, Asians and Malay. This classification remained in common usage until the mid 20th century, sometimes alongide H. s. tasmanianus for Australians. See, for example, Bailey, 1946; Hall, 1946. The division of extant human populations into taxonomic subspecies was gradually given up in the 1970s (for example, Grzimek's Animal Life Encyclopedia).
^Homo sapiens sapiens is first used in the 1940s as a synonym of Linnaeus' H. s. europaeus, i. e. Caucasoids. This usage is abandoned by the 1970s, and H. s. sapiens was now used for Cro-Magnon by authors who wished to classify Neanderthals as subspecies of H. sapiens taken in a wider sense, for example Seely.
^For example, "DMA studies have revealed that the first anatomically modern humans (H. s. sapiens) arose in Africa between 200,000 and 140,000 years ago". This usage persists alongside H. s. sapiens designating Upper Paleolithic Cro Magnon, for example. "About 200,000 years ago our own species, Homo sapiens (the thinking human), evolved [...] About 60,000 years ago we became elaborate artisans, building boats and intricate shelters; at this stage, scientists refer to us as Homo sapiens sapiens."
^"Although none of the Qesem teeth shows a suite of Neanderthal characters, a few traits may suggest some affinities with members of the Neanderthal evolutionary lineage. However, the balance of the evidence suggests a closer similarity with the Skhul/Qafzeh dental material, although many of these resemblances likely represent plesiomorphous features."
^"Currently available genetic and archaeological evidence is generally interpreted as supportive of a recent single origin of modern humans in East Africa."
^It is important to note that this is a question of conventional terminology, not one of a factual disagreement. Pääbo (2014) frames this as a debate that is unresolvable in principle, "since there is no definition of species perfectly describing the case."
^Contemporary human endocranial volume averages at 1,350 cm3 (82 cu in), with significant differences between populations, global group means range 1,085–1,580 cm3 (66.2–96.4 cu in). Neanderthal average is close to 1,450 cm3 (88 cu in) (male average 1,600 cm3 (98 cu in), female average 1,300 cm3 (79 cu in)), with a range extending up to 1,736 cm3 (105.9 cu in) (Amud 1).
^"Based on 45 long bones from maximally 14 males and 7 females, Neanderthals' height averages between 164 and 168 (males) resp. 152 to 156 cm (females). This height is indeed 12-14 cm lower than the height of post-WWII Europeans, but compared to Europeans some 20,000 or 100 years ago, it is practically identical or even slightly higher."
^Malay, 20–24 (N= m:749 f:893, Median= m:166 cm (5 ft 51⁄2 in) f:155 cm (5 ft 1 in), SD= m:6.46 cm (21⁄2 in) f:6.04 cm (21⁄2 in))
^"Specifically, genes in the LCP [lipid catabolic process] term had the greatest excess of NLS in populations of European descent, with an average NLS frequency of 20.8±2.6% versus 5.9±0.08% genome wide (two-sided t-test, P<0.0001, n=379 Europeans and n=246 Africans). Further, among examined out-of-Africa human populations, the excess of NLS [Neanderthal-like genomic sites] in LCP genes was only observed in individuals of European descent: the average NLS frequency in Asians is 6.7±0.7% in LCP genes versus 6.2±0.06% genome wide."
^Traits affected by the mutation are sweat glands, teeth, hair thickness and breast tissue.
^"We offer an alternative hypothesis that suggests that hominid expansion into regions of cold climate produced change in head shape. Such change in shape contributed to the increased cranial volume. Bioclimatic effects directly upon body size (and indirectly upon brain size) in combination with cranial globularity appear to be a fairly powerful explanation of ethnic group differences." (figure in Beals, p304)
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