5.6.3. Genus Homo

Genus Homo

One current view of the temporal and geographical distribution of hominid populations. Other interpretations differ mainly in the taxonomy and geographical distribution of hominid species.

Homo sapiens is the only extant species of its genus, Homo. While some other, extinct Homo species might have been ancestors of Homo sapiens, many were likely our “cousins”, having speciated away from our ancestral line. There is not yet a consensus as to which of these groups should count as separate species and which as subspecies. In some cases this is due to the dearth of fossils, in other cases it is due to the slight differences used to classify species in the Homo genus. The Sahara pump theory (describing an occasionally passable “wet” Sahara Desert) provides one possible explanation of the early variation in the genus Homo.Based on archaeological and paleontological evidence, it has been possible to infer, to some extent, the ancient dietary practices of variousHomo species and to study the role of diet in physical and behavioral evolution within Homo.

According to the Toba catastrophe theory to which some anthropologists and archeologists subscribe, the supereruption of Lake Toba on Sumatra island in Indonesia roughly 70,000 years ago had global consequences, killing most humans then alive and creating a population bottleneck that affected the genetic inheritance of all humans today.

H. habilis and H. gautengensis

Homo habilis lived from about 2.33 to 1.4 Ma (Gelasian Pleistocene). Homo habilis evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5–2 Ma, when it diverged from the australopithecines. Homo habilis had smaller molars and larger brains than the australopithecines, and made tools from stone and perhaps animal bones. One of the first known hominids, it was nicknamed ‘handy man’ by discoverer Louis Leakey due to its association with stone tools. Some scientists have proposed moving this species out o fHomo and into Australopithecus due to the morphology of its skeleton being more adapted to living on trees rather than to moving on two legs like Homo sapiens.

In its appearance and morphology, H. habilis is the least similar to modern humans of all species in the genus (except possibly H. rudolfensis). H. habilis was short and had disproportionately long arms compared to modern humans; however, it had a less protruding face than the australopithecines from which it is thought to have descended. H. habilis had a cranial capacity slightly less than half of the size of modern humans. Despite the ape-like morphology of the bodies, H. habilis remains are often accompanied by primitive stone tools (e.g. Olduvai Gorge, Tanzania andLake Turkana, Kenya).

Compared to australopithecines, H. habilis’ brain capacity of around 600 cm³ was on average 50% larger than australopithecines, but considerably smaller than the 1350 to 1450 cm³ range of modern Homo sapiens. These hominins were smaller than modern humans, on average standing no more than 1.3 m (4 ft 3 in) tall. The small size and rather primitive attributes have led some experts (Richard Leakey among them) to propose excluding H. habilis from the genusHomo, and renaming as “Australopithecus habilis“.

Homo habilis has often been thought to be the ancestor of the more gracile and sophisticated Homo ergaster, which in turn gave rise to the more human-appearing species, Homo erectus. Debates continue over whether H. habilis is a direct human ancestor, and whether all of the known fossils are properly attributed to the species. Some paleoanthropologists regard the taxon as invalid, made up of fossil specimens of Australopithecus and Homo. In 2007, new findings suggested that H. habilis and H. erectus coexisted and may be separate lineages from a common ancestor instead of H. erectus being descended from H. habilis.

It was considered to be the first species of the genus Homo until May 2010, when a new species, Homo gautengensis was discovered in South Africa, that most likely arose earlier than Homo habilis.

Homo gautengensis had big teeth suitable for chewing plant material. It was “small-brained” and “large-toothed,” and was “probably an ecological specialist, consuming more vegetable matter than Homo erectus, Homo sapiens, and probably even Homo habilis.” It apparently produced and used stone tools and may even have made fire, as there is evidence for burnt animal bones associated with H. gautengensis’ remains.

Curnoe believes H. gautengensis stood just over 3 feet (0.91 m) tall and weighed about 110 pounds (50 kg). It walked on two feet when on the ground, “but probably spent considerable time in trees, perhaps feeding, sleeping and escaping predators,” Curnoe said.

The researchers believe it lacked speech and language skills. Due to its anatomy and geological age, researchers think that it was a close relative of Homo sapiens but not necessarily a direct ancestor.

H. rudolfensis

Homo rudolfensis was a species of the genus Homo known only through a handful of representative fossils, the first of which was discovered by Bernard Ngeneo, a member of a team led by anthropologist Richard Leakey and zoologist Meave Leakey in 1972, at Koobi Fora on the east side of Lake Rudolf (now Lake Turkana) in Kenya. The scientific name Pithecanthropus rudolfensis was proposed in 1978 by V. P. Alekseyev. It was later changed to Homo rudolfensis by Bernard Wood, for the specimen Skull 1470 (KNM ER 1470). On 8 August 2012, a team led by Meave Leakey announced the discovery of a face and two jawbones belonging to H. rudolfensis.

The skull was at first incorrectly dated at nearly three million years old, predating the Homo habilis species. Since then, the estimate has been corrected to 1.9 million years, but the differences in this skull, when compared to others of the Homo habilis species, are said to be too pronounced, leading to the presumption of a Homo rudolfensis species, contemporary with Homo habilis. It is not certain whether H. rudolfensis was ancestral to the later species of Homo, or whether H. habilis was, or whether some third species, yet undiscovered, was ancestral to the later Homo line.
In March 2007, a team led by Timothy Bromage, an anthropologist at New York University, reconstructed the skull of KNM-ER 1470. The new construction looked very ape-like (possibly due to an exaggerated rotation of the skull) and the cranial capacity based on the new construction was reported to be downsized from 752 cm³ to about 526 cm³, although this seemed to be a matter of some controversy. Bromage said his team’s reconstruction included biological knowledge not known at the time of the skull’s discovery, of the precise relationship between the sizes of eyes, ears, and mouth in mammals.

A newer publication by Bromage has since further downsized the cranial capacity estimate from 752 cm³ to 700 cm³.

In August 2012, a team led by Meave Leakey published an academic paper in Nature announcing three additional H. rudolfensis fossils from northern Kenya had been found: two jawbones with teeth and a face. The face (fossil KNM-ER 62000) was of a juvenile, but had features in common with KNM-ER 1470, suggesting the latter skull’s uniqueness is due to being a separate species, rather than a large male H. habilis. Team member Fred Spoor described the face as “incredibly flat”, with a straight line from the eye socket to the incisor tooth. The jawbones, which appeared to match KNM-ER 1470 and KNM-ER 62000, were also shorter and more rectangular than known H. habilis specimens.

The fossils were dated to about two million years ago, being contemporaneous with H. habilis. According to Leakey et al., “the new fossils confirm the presence of two contemporary species of early Homo [that is, habilis and rudolfensis], in addition to Homo erectus, in the early Pleistocene of eastern Africa”.

H. erectus and H. ergaster

Homo erectus (meaning “upright man,” from the Latin ērĭgĕre, “to put up, set upright”) is an extinct species of hominid that lived from the end of the Pliocene epoch to the later Pleistocene, with the earliest first fossil evidence dating to around 1.8 million years ago and the most recent to around 300,000 years ago.

The first hypothesis is that H. erectus migrated from Africa during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 2.0 million years ago, and dispersed throughout much of the Old World. Fossilized remains 1.8 to 1 million years old have been found in Africa (e.g., Lake Turkana and Olduvai Gorge), Georgia, Europe (Spain), Indonesia (e.g., Sangiran and Trinil), Vietnam, China (e.g., Shaanxi) and India.

The second hypothesis is that H. erectus evolved in Eurasia and then migrated to Africa. The species occupied a Caucasus site called Dmanisi, in Georgia, from 1.85 million to 1.77 million years ago, at the same time or slightly before the earliest evidence in Africa. Excavations found 73 stone tools for cutting and chopping and 34 bone fragments from unidentified creatures.

The first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in 1891 on the Indonesian island of Java. He originally named the material Pithecanthropus erectus based on its morphology, which he considered to be intermediate between that of humans and apes. Homo erectus (H erectus) lived from about 1.8 Ma to about 70,000 years ago (which would indicate that they were probably wiped out by the Toba catastrophe; however, Homo erectus soloensis and Homo floresiensis survived it). Often the early phase, from 1.8 to 1.25 Ma, is considered to be a separate species, Homo ergaster, or it is seen as a subspecies of Homo erectus,Homo erectus ergaster.

Many paleoanthropologists still debate the definition of H. erectus and H. ergaster as separate species. Several scholars suggested dropping the taxon Homo erectus and instead equatingH. erectus with the archaic H. sapiens. Some call H. ergaster the direct African ancestor of H. erectus, proposing that it emigrated out of Africa and immigrated to Asia, branching into a distinct species. Most dispense with the species name ergaster, making no distinction between such fossils as the Turkana Boy and Peking Man. Although “Homo ergaster” has gained some acceptance as a valid taxon, these two are still usually defined as distinct African and Asian populations of the larger species H. erectus.

The extant model of comparison is very important, and selecting appropriate species can be difficult. (For example, the morphological variation among the global population of H. sapiens is small, and our own special diversity may not be a trustworthy comparison.) As an example, fossils found in Dmanisi in the Republic of Georgia were originally described as belonging to another closely related species, Homo georgicus, but subsequent examples showed their variation to be within the range of Homo erectus, and they are now classified as Homo erectus georgicus.

H. erectus had a cranial capacity greater than that of Homo habilis (although the Dmanisi specimens have distinctively small crania): the earliest remains show a cranial capacity of 850 cm³, while the latest Javan specimens measure up to 1100 cm³, overlapping that of H. sapiens.; the frontal bone is less sloped and the dental arcade smaller than the australopithecines’; the face is more orthognatic (less protrusive) than either the australopithecines’ or H. habilis’s, with large brow-ridges and less prominent zygomata (cheekbones). These early hominins stood about 1.79 m (5 ft 10 in), and were more robust than modern humans.

The sexual dimorphism between males and females was slightly greater than seen in H. sapiens, with males being about 25% larger than females. However, their dimorphism is drastically lesser than that of the earlier Australopithecus genus. The discovery of the skeleton KNM-WT 15000, “Turkana boy” (Homo ergaster), made near Lake Turkana, Kenya by Richard Leakey and Kamoya Kimeu in 1984, is one of the most complete hominid-skeletons discovered, and has contributed greatly to the interpretation of human physiological evolution.

Homo ergaster. (also “African Homo erectus“) is an extinct chronospecies of Homo that lived in eastern and southern Africa during the early Pleistocene, between 1.8 million and 1.3 million years ago. There is still disagreement on the subject of the classification, ancestry, and progeny of H. ergaster, but it is now widely accepted to be the direct ancestor of later hominids such as Homo heidelbergensis, Homo sapiens, and Homo neanderthalensis and Asian Homo erectus.

It is one of the earliest members of the genus Homo, possibly ancestral to, or sharing a common ancestor with, Homo erectus. Some paleoanthropologists consider H. ergaster to be simply the African variety of H. erectus; this leads to the use of the term “Homo erectus sensu stricto” for the Asian H. Erectus, and “Homo erectus sensu lato” for the larger species comprising both the early African populations (H. ergaster) and the Asian populations.

The binomial name was published in 1975 by Groves and Mazák. The second part, “ergaster”, is derived from the Ancient Greek ἐργαστήρ “workman”, in reference to the comparatively advanced lithic technology developed by the species, introducing the Acheulean industry.

H. ergaster may be distinguished from H. erectus by its thinner skull-bones and lack of an obvious supraorbital foramen. It may be distinguished from Homo heidelbergensis by its thinner bones, more protrusive face, and lower forehead. Derived features separating it from earlier species include reduced sexual dimorphism, a smaller, more orthognathous (less protrusive) face, a smaller dental arcade, and a larger cranial capacity (700-900cm³ in earlier ergaster-specimens, and 900-1100 in later specimens). It is estimated that male H. ergaster stood 1.89 meters (6 ft 2 in) tall. Remains have been found in Tanzania, Ethiopia, Kenya, and South Africa.

H. cepranensis and H. antecessor

These are proposed as species that may be intermediate between H. erectus and H. heidelbergensis.

Homo antecessor is an extinct human species (or subspecies) dating from 1.2 million to 800,000 years ago and is one of the earliest known human varieties in Europe.

Various archaeologists and anthropologists have debated how H. antecessor related to otherHomo species in Europe, with suggestions that it was an evolutionary link between H. ergaster and H. heidelbergensis, although Richard Klein believes that it was instead a separate species that evolved from H. ergaster. Others believe that H. antecessor is the same species as H. heidelbergensis, who inhabited Europe from 600,000 to 250,000 years ago in the Pleistocene.

The best-preserved fossil is a maxilla that belonged to a 10-year-old individual found in Spain. Based on palaeomagnetic measurements, it is thought to be older than 780–857 ka. The average brain was 1,000 cm³ in volume. In 1994 and 1995, 80 fossils of six individuals that may have belonged to the species were found in Atapuerca, Spain. At the site were numerous examples of cuts where the flesh had been flensed from the bones, which indicates that H. antecessor may have practised cannibalism.

H. antecessor was about 1.6-1.8 m (5½-6 feet) tall, and males weighed roughly 90 kg (200 pounds). Their brain sizes were roughly 1,000–1,150 cm³, smaller than the 1,350 cm³ average of modern humans. Due to its scarcity, very little more is known about the physiology of H. antecessor, yet it was likely to have been more robust than H. heidelbergensis.

Homo cepranensis is a proposed name for a human species, known from only one skull cap discovered in 1994. The fossil was discovered by archeologist Italo Biddittu and was nicknamed “Ceprano Man” after a nearby town in the province of Frosinone, 89 kilometers Southeast of Rome, Italy.

The age of the fossil is estimated to be between 350,000 to 500,000 years old. An adjacent site, Fontana Ranuccio, was dated to 487,000 +/- 6000 years and Muttoni et al. suggest that Ceprano is most likely 450,000 years old. The cranial features on the bone seem to be intermediate between those found on Homo erectus and those of later species such as Homo heidelbergensis which dominated Europe long before Homo neanderthalensis. A 2011 study suggested it was ancestral to Homo neanderthalensis. There is not yet enough material to make a complete analysis of the individual.

H. heidelbergensis

Homo heidelbergensis (“Heidelberg Man”, named after the University of Heidelberg) is an extinct species of the genus Homo which may be^[1] the direct ancestor of both Homo neanderthalensis in Europe and Homo sapiens.^{[2][dubious – discuss]} The best evidence found for these hominins dates them between 600,000 and 400,000 years ago.H. heidelbergensis stone tool technology was very close to that of the Acheulean tools used by Homo erectus.

Both H. antecessor and H. heidelbergensis are likely to be descended from themorphologically very similar Homo ergaster from Africa. But because H. heidelbergensishad a larger brain-case — with a typical cranial volume of 1100–1400 cm³ overlapping the 1350 cm³ average of modern humans — and had more advanced tools and behavior, it has been given a separate species classification. Male heidelbergensis averaged about 5 ft 9 in (1.75 m) tall and 136 lb (62 kg). Females averaged 5 ft 2 in (1.57 m) and 112 lb (51 kg). A reconstruction of 27 complete human limb bones found in Atapuerca (Burgos, Spain) has helped to determine the height of H. heidelbergensis compared toHomo neanderthalensis, the conclusion was that most H. heidelbergensis averaged about 170 cm (5ft 7in) in height and were only slightly taller than neanderthals. According to Lee R. Berger of the University of Witwatersrand, numerous fossil bones indicate some populations of Heidelbergensis were “giants” routinely over 2.13 m (7 ft) tall and inhabited South Africa between 500,000 and 300,000 years ago.

[edit]H. rhodesiensis, and the Gawis cranium

H. rhodesiensis, estimated to be 300,000–125,000 years old. Most current researchers place Rhodesian Man within the group of Homo heidelbergensis, though other designations such as Archaic Homo sapiens and Homo sapiens rhodesiensis have been proposed.

In February 2006 a fossil, the Gawis cranium, was found which might possibly be a species intermediate between H. erectus and H. sapiens or one of many evolutionary dead ends. The skull from Gawis, Ethiopia, is believed to be 500,000–250,000 years old. Only summary details are known, and the finders have not yet released a peer-reviewed study. Gawis man’s facial features suggest its being either an intermediate species or an example of a “Bodo man” female.[92]

[edit]Neanderthal and Denisova hominin

Main articles: Neanderthal and Denisova hominin

Dermoplastic reconstruction of a Neanderthal

H. neanderthalensis, alternatively designated as Homo sapiens neanderthalensis,[93] lived in Europe and Asia from 400,000[94] to about 30,000 years ago. Evidence from sequencingmitochondrial DNA indicated that no significant gene flow occurred between H. neanderthalensisand H. sapiens, and, therefore, the two were separate species that shared a common ancestor about 660,000 years ago.[95][96][97] However, the 2010 sequencing of the Neanderthal genome indicated that Neanderthals did indeed interbreed with anatomically modern humans circa 45,000 to 80,000 years ago (at the approximate time that modern humans migrated out from Africa, but before they dispersed into Europe, Asia and elsewhere).[98]

Nearly all modern non-African humans have 1% to 4% of their DNA derived from Neanderthal DNA,[98] and this finding is consistent with recent studies indicating that the divergence of some human alleles dates to one Ma, although the interpretation of these studies has been questioned.[99][100] Competition from Homo sapiens probably contributed to Neanderthal extinction.[101] They could have co-existed in Europe for as long as 10,000 years, during which human populations exploded vastly outnumbering Neanderthals, possibly outcompeting them by sheer numerical strength.[102]

In 2008, archaeologists working at the site of Denisova Cave in the Altai Mountains of Siberia uncovered a small bone fragment from the fifth finger of a juvenile member of a population now referred to as Denisova hominins, or simply Denisovans.[103] Artifacts, including a bracelet, excavated in the cave at the same level were carbon dated to around 40,000 BP. As DNA had survived in the fossil fragment due to the cool climate of the Denisova Cave, both mtDNA and nuclear genomic DNA were sequenced.[12][104]

While the divergence point of the mtDNA was unexpectedly deep in time,[105] the full genomic sequence suggested the Denisovans belonged to the same lineage as Neanderthals, with the two diverging shortly after their line split from that giving rise to modern humans.[12] Modern humans are known to have overlapped with Neanderthals in Europe for more than 10,000 years, and the discovery raises the possibility that Neanderthals, modern humans and the Denisova hominin may have co-existed. The existence of this distant branch creates a much more complex picture of humankind during the Late Pleistocene than previously thought.[104][106] Evidence has also been found for as much as 6% of the genomes of some modern Melanesians to derive from Denisovans, indicating limited interbreeding in Southeast Asia.[107][108]

Alleles thought to have originated in Neanderthal and the Denisova hominin have been identified at several genetic loci in the genomes of modern humans outside of Africa. HLA types from Denisovans and Neanderthal represent more than half the HLA alleles of modern Eurasians,[14] indicating strong positive selection for these introgressed alleles.

[edit]H. floresiensis

Main article: Homo floresiensis

H. floresiensis, which lived from approximately 100,000 to 12,000 before present, has been nicknamed hobbit for its small size, possibly a result of insular dwarfism.[109] H. floresiensis is intriguing both for its size and its age, being an example of a recent species of the genus Homo that exhibits derived traits not shared with modern humans. In other words, H. floresiensis shares a common ancestor with modern humans, but split from the modern human lineage and followed a distinct evolutionary path. The main find was a skeleton believed to be a woman of about 30 years of age. Found in 2003 it has been dated to approximately 18,000 years old. The living woman was estimated to be one meter in height, with a brain volume of just 380 cm3 (considered small for a chimpanzee and less than a third of the H. sapiens average of 1400 cm3).[citation needed]

However, there is an ongoing debate over whether H. floresiensis is indeed a separate species.[110] Some scientists hold that H. floresiensis was a modern H. sapiens with pathological dwarfism.[111] This hypothesis is supported in part, because some modern humans who live on Flores, the island where the skeleton was found, are pygmies. This, coupled with pathological dwarfism, could possibly create a hobbit-like human. The other major attack on H. floresiensis is that it was found with tools only associated with H. sapiens.[111]

The hypothesis of pathological dwarfism, however, fails to explain additional anatomical features that are unlike those of modern humans (diseased or not) but much like those of ancient members of our genus. Aside from cranial features, these features include the form of bones in the wrist, forearm, shoulder, knees, and feet. Additionally, this hypothesis fails to explain the find of multiple examples of individuals with these same characteristics, indicating they were common to a large population, and not limited to one individual.

[edit]H. sapiens

Main article: Archaic Homo sapiens

H. sapiens (the adjective sapiens is Latin for “wise” or “intelligent”) have lived from about 250,000 years ago to the present. Between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, the trend in skull expansionand the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens. The direct evidence suggests there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa. A subsequent migration within and out of Africa eventually replaced the earlier dispersed H. erectus. This migration and origin theory is usually referred to as the recent single origin or Out of Africa theory. Current evidence does not preclude some multiregional evolution or some admixture of the migrant H. sapiens with existing Homo populations. This is a hotly debated area of paleoanthropology.

Current research has established that humans are genetically highly homogenous; that is, the DNA of individuals is more alike than usual for most species, which may have resulted from their relatively recent evolution or the possibility of a population bottleneckresulting from cataclysmic natural events such as the Toba catastrophe.[112][113][114] Distinctive genetic characteristics have arisen, however, primarily as the result of small groups of people moving into new environmental circumstances. These adapted traits are a very small component of the Homo sapiens genome, but include various characteristics such as skin color and nose form, in addition to internal characteristics such as the ability to breathe more efficiently at high altitudes.

H. sapiens idaltu, from Ethiopia, is an extinct sub-species from about 160,000 years ago.