Early modern human, or anatomically modern human, are terms used to distinguish Homo sapiens (the only extant Hominina species) that are anatomically consistent with the range of phenotypes seen in contemporary humans, from extinct archaic human species. This distinction is useful especially for times and regions where anatomically modern and archaic humans co-existed, for example, in Paleolithic Europe. Among the oldest known remains of Homo sapiens are those found at the Omo-Kibish I archaeological site in south-western Ethiopia, dating to about 233,000 to 196,000 years ago, the Florisbad Skull found at the Florisbad archaeological and paleontological site in South Africa, dating to about 259,000 years ago, and the Jebel Irhoud site in Morocco, dated about 315,000 years ago.
Extinct species of the genus Homo include Homo erectus (extant from roughly 2,000,000 to 100,000 years ago) and a number of other species (by some authors considered subspecies of either H. sapiens or H. erectus). The divergence of the lineage leading to H. sapiens out of ancestral H. erectus (or an intermediate species such as Homo antecessor) is estimated to have occurred in Africa roughly 500,000 years ago. The earliest fossil evidence of early modern humans appears in Africa around 300,000 years ago, with the earliest genetic splits among modern people, according to some evidence, dating to around the same time. Sustained archaic human admixture with modern humans 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.
Name and taxonomy
The binomial name Homo sapiens was coined by Linnaeus, 1758. The Latin noun homō (genitive hominis) means "human being", while the participle sapiēns means "discerning, wise, sensible", or taken together essentially "intelligent human".
The species was initially thought to have emerged from a predecessor within the genus Homo around 300,000 to 200,000 years ago. 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.
Estimates for the split between the Homo sapiens line and combined Neanderthal/Denisovan line range from between 503,000 and 565,000 years ago; between 550,000 and 765,000 years ago; and (based on rates of dental evolution) possibly more than 800,000 years ago.
Extant human populations have historically been divided into subspecies, but since around the 1980s, the consensus has been to subsume all extant groups into a single species, H. sapiens, avoiding division into subspecies altogether.
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.
All humans are considered to be a part of the subspecies H. sapiens sapiens, a designation which has been a matter of debate since a species is usually not given a subspecies category unless there is evidence of multiple distinct subspecies.
Age and speciation process
Derivation from H. erectus
The divergence of the lineage that would lead to H. sapiens out of archaic human varieties derived from H. erectus, is estimated as having taken place over 500,000 years ago (marking the split of the H. sapiens lineage from ancestors shared with other known archaic hominins). But the oldest split among modern human populations (such as the Khoisan split from other groups) has been recently dated to between 350,000 and 260,000 years ago, and the earliest known examples of H. sapiens fossils also date to about that period, including the Jebel Irhoud remains from Morocco (ca. 300,000 or 350–280,000 years ago), the Florisbad Skull from South Africa (ca. 259,000 years ago), and the Omo remains from Ethiopia (ca. 195,000, or, as more recently dated, ca. 233,000 years ago).; ; ;
An mtDNA study in 2019 proposed an origin of modern humans in Botswana (and a Khoisan split) of around 200,000 years. However, this proposal has been widely criticized by scholars, with the recent evidence overall (genetic, fossil, and archaeological) supporting an origin for H. sapiens approximately 100,000 years earlier and in a broader region of Africa than the study proposes.
In September 2019, scientists proposed that the earliest H. sapiens (and last common human ancestor to modern humans) arose between 350,000 and 260,000 years ago through a merging of populations in East and South Africa.
An alternative suggestion defines H. sapiens cladistically 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).
The derivation of a comparatively homogeneous single species of H. sapiens from more diverse varieties of archaic humans (all of which were descended from the early dispersal of H. erectus some 1.8 million years ago) was debated in terms of two competing models during the 1980s: "recent African origin" postulated the emergence of H. sapiens from a single source population in Africa, which expanded and led to the extinction of all other human varieties, while the "multiregional evolution" model postulated the survival of regional forms of archaic humans, gradually converging into the modern human varieties by the mechanism of clinal variation, via genetic drift, gene flow and selection throughout the Pleistocene.
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, originally 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.Human evolution: the fossil evidence in 3D, by Philip L. Walker and Edward H. Hagen, Dept. of Anthropology, University of California, Santa Barbara. Retrieved April 5, 2005. H. neanderthalensis, which became extinct about 40,000 years ago, was also at one point considered to be 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.
Early Homo sapiens
The term Middle Paleolithic is intended to cover the time between the first emergence of H. sapiens (roughly 300,000 years ago) and the period held by some to mark the emergence of full behavioral modernity (roughly by 50,000 years ago, corresponding to the start of the Upper Paleolithic).
Many of the early modern human finds, like those of Jebel Irhoud, Omo, Herto, Florisbad, Skhul, 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 humans.
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. 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).
Fossil teeth found at Qesem Cave (Israel) and dated to between 400,000 and 200,000 years ago have been compared to the dental material from the younger (120,000–80,000 years ago) Skhul and Qafzeh hominins.
Dispersal and archaic admixture
Dispersal of early H. sapiens began soon after its emergence, as evidenced by the North African Jebel Irhoud finds (dated to around 315,000 years ago). There is indirect evidence for H. sapiens presence in West Asia around 270,000 years ago.
The Florisbad Skull from Florisbad, South Africa, dated to about 259,000 years ago, has also been classified as representing early H. sapiens.
In September 2019, scientists proposed that the earliest H. sapiens (and last common human ancestor to modern humans) arose between 350,000 and 260,000 years ago through a merging of populations in East and South Africa.