Origins

We are Hominids, or Hominidae, also known as great apes.

Our taxonomic family of primates includes four extant genera: the chimpanzees (Pan) with two species; gorillas (Gorilla) with two species; humans (Homo) with one species; and orangutans (Pongo) with two species.

Homininae, a subfamily of Hominidae that includes members of hominini—humans, as well as gorillas, chimpanzees, bonobos and some extinct relatives—comprises all hominids that arose after the split from orangutans (Ponginae).

A number of known extinct genera are grouped with humans in the Homininae subfamily, others with orangutans in the Ponginae subfamily.

The most recent common ancestor of the Hominidae lived roughly fourteen million years ago, when the ancestors of the orangutans speciated from the ancestors of the other three genera.

The subtribe Hominina is the "human" branch, including the genus Homo, which has its beginnings in this eon, which spans a quarter of a million years.

The fossil record suggests that individuals of the species Gigantopithecus blacki are the largest apes that ever lived, standing up to three meters (nine point eight feet feet) and weighing up to five hundred and forty kilograms (one thousand one hundred and ninety pounds).

Gigantopithecus, having come into existence perhaps nine million years ago, exists to as recently one hundred thousand years ago in what is now Nepal, China, India, and Vietnam.

This places Gigantopithecus in the same time frame and geographical location as several hominin species.

In addition to the Homo genus to which we belong, other members of the family include Orrorin, Ardipithecus, Kenyanthropus, and the australopithecines Australopithecus and Paranthropus.

The name of the genus Orrorin means "original man" in Tugen, and the name of the only classified species, O. tugenensis, derives from Tugen Hills in Kenya, where the first fossil was found in 2000, followed by another score or so more in the ensuing years.

Apparently a climber of trees, Orrorin lives in dry evergreen forest environment estimated at six point one million to five point seven million years ago (Mya).

If Orrorin proves to be a direct human ancestor, then australopithecines such as Australopithecus afarensis ("Lucy") may be considered a side branch of the hominid family tree: Orrorin is both earlier, by almost three million years, and more similar to modern humans than is A. afarensis.

The relationship of the Ardipithecus genus to human ancestors, and whether it is a hominin, or not, is unknown.

The literature describes two species: A. kadabba, dated to approximately five point sixmillion years ago (late Miocene), and A. ramidus, which lived about four point four million years ago during the early Pliocene.

Like most hominids, but unlike all previously recognized hominins, it had a grasping hallux or big toe adapted for locomotion in the trees.

It is not confirmed how much other features of its skeleton reflect adaptation to bipedalism on the ground as well.

Like later hominins, Ardipithecus had reduced canine teeth.

The brain of Ardipithecus ramidus, measuring between three hundred and three hundred and fifty square centimeters, is slightly smaller than a modern bonobo or female common chimpanzee brain, but much smaller than the brain of australopithecines like Lucy (around four hundred to five hundred and fifty square kilometers) and roughly twenty percent the size of the modern Homo sapiens brain.

Kenyanthropus platyop, a three point five million to three point two million year-old (Pliocene) hominin fossil discovered in Lake Turkana, Kenya, is believed to have lived in a “mosaic” environment of grassland and some forested areas.

In contrast, their close relative, A. afarensis, found in sites such as Laetoli, Tanzania, and Hadar, Ethiopia, are believed to have spent a lot of time among trees.

Maeve Leakey proposed in 2001 that the fossil represents an entirely new hominine genus, while others classify it as a separate species of Australopithecus, Australopithecus platyops, and yet others interpret it as an individual of Australopithecus afarensis.

Details on the origins of all the peoples that make up the population of highland Ethiopia are still matters for research and debate in the early 1990s.

Anthropologists believe that East Africa's Great Rift Valley is the site of humankind's origins. (The valley traverses Ethiopia from southwest to northeast.)

In 1974 archaeologists excavating sites in the Awash River will valley discover three and a  half-million-year-old fossil skeletons, which they name Australopithecus afarensis.

These earliest known hominids stand upright, live in groups, and have adapted to living in open areas rather than in forests.

All humans originate from East Africa, according to the theory of recent African origin of modern humans, the position held within a majority of the scientific community.

Some of the earliest fossilized hominid remains have been found in East Africa, including those found in Awash Valley of Ethiopia, Koobi Fora in Kenya and Olduvai Gorge in Tanzania.

Human-like footprints from western Crete, close to the village of Trachilos, west of Kissamos, in the Chania Prefecture, are approximately 5.7 million years old and are made at a time when previous research puts our ancestors in Africa—with ape-like feet.

Human feet have a very distinctive shape, different from all other land animals.

The combination of a long sole, five short forward-pointing toes without claws, and a hallux ("big toe") that is larger than the other toes, is unique.

The feet of our closest relatives, the great apes, look more like a human hand with a thumb-like hallux that sticks out to the side.

These footprints, from Trachilos in western Crete, have an unmistakably human-like form.

This is especially true of the toes.

The big toe is similar to our own in shape, size and position; it is also associated with a distinct 'ball' on the sole, which is never present in apes.

At approximately 5.7 million years, these footprints are younger than the oldest known fossil hominin, Sahelanthropus from Chad, and contemporary with Orrorin from Kenya, but more than a million years older than Ardipithecus ramidus with its ape-like feet.

The Trachilos footprints are securely dated using a combination of foraminifera (marine microfossils) from over- and underlying beds, plus the fact that they lie just below a very distinctive sedimentary rock formed when the Mediterranean sea briefly dried out, 5.6 million years ago.

During the time when the Trachilos footprints were made, a period known as the late Miocene, the Sahara Desert did not exist; savannah-like environments extended from North Africa up around the eastern Mediterranean.

Furthermore, Crete had not yet detached from the Greek mainland.

It is thus not difficult to see how early hominins could have ranged across south-east Europe and well as Africa, and left their footprints on a Mediterranean shore that will one day form part of the island of Crete.

Lucy, discovered in the Awash Valley of Ethiopia's Afar region, is considered the world's second oldest, but most complete and best preserved, adult Australopithecine fossil.

Lucy's taxonomic name, Australopithecus afarensis, means 'southern ape of Afar', and refers to the Ethiopian region where the discovery was made.

Lucy is estimated to have lived three point two million years ago.

There have been many other notable fossil findings in the country, including another early hominin, Ardipithicus ramidus (Ardi).

East Africa, and more specifically the general area of Ethiopia, is widely considered the site of the emergence of early Homo sapiens in the Middle Paleolithic.

Humans—the genus Homo—may have descended from australopithecine ancestors, while the genus Ardipithecus is a possible ancestor of the australopithecines.

Australopithecine is the general term for any species in the related genera of Australopithecus and Paranthropus.

They are bipedal and dentally similar to humans, but with a brain size not much larger than that of modern apes.

It appears that the Australopithecus genus evolved in eastern Africa around four million years ago before spreading throughout the continent and eventually becoming extinct two million years ago.

During this time period several australopith species emerges, including Australopithecus afarensis, A. africanus, A. anamensis, A. bahrelghazali, A. garhi and A. sediba.

Opinions differ as to whether the species aethiopicus, boisei, and robustus should be included within the genus Australopithecus, and there is no current consensus as to whether they should be placed in the distinct group of hominids now called the "robust australopiths” or, Paranthropus (Greek para, "beside"; Greek anthropos, “human”).

The fossil record seems to indicate that Australopithecus is the common ancestor of Paranthropus, and most likely the genus Homo, which includes modern humans.

Though the intelligence of these early hominids is likely no more sophisticated than modern apes, the bipedal stature is the key evidence that distinguishes the group from previous primates, who were quadrupeds.

Most species of Australopithecus are no more adept at tool use than modern nonhuman primates, yet modern African apes, chimpanzees, and most recently gorillas, have been known to use crack open nuts with stones and use long sticks to dig for termites in mounds, and chimpanzees have been observed using spears (not thrown) for hunting.

However, some have argued that A. garhi used stone tools due to a loose association of this species and butchered animal remains.

Trace element studies of the strontium/calcium ratios in robust australopith fossils  in 1992 suggested the possibility of animal consumption, as they did in 1994 using stable carbon isotopic analysis.

Paranthropus stands roughly one point three to one point four meters (four and a quarter to four and a half feet) tall and is well muscled.

More massively built craniodentally, Paranthropus tends to sport gorilla-like sagittal crests on the cranium that anchor massive temporalis muscles of mastication.

The emergence of the robusts could be either a display of divergent or convergent evolution.

Australopithecus afarensis and A. anamensis had, for the most part, disappeared by the time Paranthropus first appears, roughly two point seven million years ago, sharing the earth with some early examples of the Homo genus, such as Homo habilis, H. ergaster, and possibly even H. erectus.

Most species of Paranthropus have significantly larger braincases than Australopithecus, with a brain about forty percent of the size of a modern human.

Paranthropus is associated with stone tools both in southern and eastern Africa, although there is considerable debate whether they were made and utilized by these robust australopithecines or contemporaneous Homo.

Most believe that early Homo was the toolmaker, but hand fossils from Swartkrans, South Africa, indicate that the hand of this robust species was also adapted for precision grasping and tool use.

Most Paranthropus species seem almost certainly neither to have used language nor to have controlled fire, although they are directly associated with the latter at Swartkrans.

Its physiology specifically tailored to a diet of grubs and plants, Paranthropus is thought to have lived in wooded areas rather than the grasslands of the Australopithecus.

This would have made it more reliant on favorable environmental conditions than members of the genus Homo, such as Homo habilis, which would eat a much wider variety of foods.

Therefore, due to poor adaptation, Paranthropus boisei/Robust Australopithecus dies out, leaving no descendants.

The Quaternary Period, the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present.

Typically defined by the cyclic growth and decay of continental ice sheets driven by Milankovitch cycles and the associated climate and environmental changes that occurred, the Quaternary Period is divided into two epochs: the Pleistocene and the Holocene (eleven thousand seven hundred years ago to today).

The Pleistocene spans the world's recent period of repeated glaciations.

With the onset of the Quaternary glaciation, the first of the several ice ages to follow, decreasing oceanic evaporation results in a drier climate in East Africa and an expansion of the savanna at the expense of forests.

Reduced availability of fruits forces some Australopithecines to unlock new food sources found in the drier savanna climate, representing a move from the mostly frugivorous or omnivorous diet of Australopithecus to the carnivorous scavenging lifestyle of early Homo.

Paranthropus species are still present in the beginning of the Pleistocene, along with early human ancestors, but they disappear during the lower Paleolithic.

The Lower Paleolithic, the earliest subdivision of the Paleolithic or Old Stone Age, begins around two and a half million million years ago when the first evidence of craft and use of stone tools by hominids appears in the current archaeological record.

The genus Homo, which includes modern humans and species closely related to them, is estimated to be about two point three to two point four million years old, evolving from australopithecine ancestors with the appearance of Homo habilis.

Specifically, H. habilis is considered the direct descendant of Australopithecus garhi, a gracile species that lived about two and a half million years ago.

The most salient physiological development between the two species is the increase in cranial capacity, from about four hundred and fifty cubic centimeters (twenty-seven cubic inches) in A. garhi to six hundred cubic centimeters (thirty-seven cubic inches) in H. habilis.

Homo gautengensis is, as of May 2010, the earliest recognized species in the genus Homo.

While earlier fossils belong to the genus Homo, none have yet been classified in any species.

Analysis announced in May 2010 of a partial skull found decades earlier in South Africa's Sterkfontein Caves near Johannesburg identified the species, named Homo gautengensis by anthropologist Dr Darren Curnoe of the UNSW School of Biological, Earth and Environmental Sciences.

While earlier fossils belong to the genus Homo, none have yet been classified in any species.

The species' first remains were originally discovered in 1977 but had been left largely ignored.

They had been catalogued Stw 53 and were noted as being anomalous.

Identification of H. gautengensis was based on partial skulls, several jaws, teeth and other bones found at various times at the Caves.

It emerged over two million years ago and died out approximately six hundred thousand years years ago, and is believed to have arisen earlier than Homo habilis.

According to Curnoe, who led the research project, 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 and South African paleoanthropologist colleague Phillip Tobias believe H. gautengensis stood just over three feet tall and weighed about one hundred and ten pounds.

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.

Homo habilis (“Handy-man") lives from approximately two point three to one point four million years ago at the beginning of the Pleistocene period.

With a cranial capacity slightly less than half of the size of modern humans, standing no more than one point three meters meters four feet three inches) tall, and with disproportionately long arms compared to modern humans, it has a less protruding face than the australopithecines from which it is thought to have descended.

Despite the ape-like morphology of the bodies, primitive stone tools often accompany H. habilis remains.

Homo habilis has often been thought to be the ancestor of the more gracile and sophisticated Homo ergaster, which in turn gives rise to the more human-appearing species, Homo erectus.

Some experts propose excluding H. habilis from the genus Homo, and renaming as "Australopithecus habilis.” Debates continue over whether H. habilis is a direct human ancestor, and whether all of the known fossils are properly attributed to the species.

New findings in 2007, however, suggest that the two species coexisted and may be separate lineages from a common ancestor instead of H. erectus being descended from H. habilis.