It took another 20 years before Dart's claims were taken seriously. This was after other similar skeletons had been found. The most common view of the time was that a large brain evolved "before" bipedality, the ability to walk on two feet more or less upright. It was thought that intelligence similar to that of modern humans was necessary for bipedalism. This turned out to be wrong: bipedality came first.
The australopithecines are now thought to be immediate ancestors of the genus "Homo", the group to which modern humans belong. Both australopithecines and "Homo sapiens" are part of the tribe Hominini, but recent data has brought into doubt the position of "A. africanus" as a direct ancestor of modern humans; it may well have been a cousin. The australopithecines were originally classified as either gracile or robust. The robust variety of "Australopithecus" has since been reclassified as "Paranthropus", although it is still regarded as a subgenus of "Australopithecus" by some authors.
In the 1930s, when the robust specimens were first described, the "Paranthropus" genus was used. During the 1960s, the robust variety was moved into "Australopithecus". The recent trend has been back to the original classification as a separate genus.
It was Carolus Linnaeus who chose the name "Homo". Today, there is only one species in the genus: "Homo sapiens". There were other species, but they became extinct.
The figure shows where some of them lived and at what time. Some of the other species might have been ancestors of "H. sapiens". Many were likely our "cousins", they developed away from our ancestral line.
Anthropologists are still investigating the exact line of descent. A consensus on which should count as separate species and which as subspecies has not been reached yet. In some cases this is because there are very few fossils, in other cases it is due to the slight differences used to classify species in the "Homo" genus.
The evolution of the genus "Homo" took place mostly in the Pleistocene. The whole genus is characterised by its use of stone tools, initially crude, and becoming ever more sophisticated. So much so that in archaeology and anthropology the Pleistocene is usually referred to as the Palaeolithic, or the Stone Age.
"Homo habilils" was likely the first species of Homo. It developed from the Australopithecus, about 2.5 million years ago. It lived until about 1.4 million years ago. It had smaller molars (back teeth) and larger brains than the Australopithecines.
There are two proposed species that lived from 1.9 to 1.6 million years ago. Their relation has not been clarified. One of them is called "Homo rudolfensis". It is known from a single incomplete skull from Kenya. Scientists have suggested that this was just another habilis, but this has not been confirmed. The other is currently called "Homo georgicus". It is from Georgia and may be an intermediate form between "H. habilis" and "H. erectus", or a sub-species of "H. erectus".
"Homo erectus" was first discovered on the island of Java in Indonesia, in 1891. The discoverer, Eugene Dubois originally called it "Pithecanthropus erectus" based on its morphology that he considered to be intermediate between that of humans and apes. Homo erectus lived from about 1.8 million to 70,000 years ago. The earlier specimens (from 1.8 to 1.2 million years ago) are sometimes seen as a different species, or a subspecies. called "Homo ergaster", or "Homo erectus ergaster'.
In the early Pleistocene, 1.5–1 mya, in Africa, Asia, and Europe, presumably, some populations of "Homo habilis" evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, "H. erectus". In addition "H. erectus" was the first human ancestor to walk truly upright. This was made possible by the evolution of locking knees and a different location of the foramen magnum (the hole in the skull where the spine enters). They may have used fire to cook their meat.
A famous example of "Homo erectus" is Peking Man; others were found in Asia (notably in Indonesia), Africa, and Europe. Many paleoanthropologists are now using the term "Homo ergaster" for the non-Asian forms of this group. They reserve "H. erectus" only for those fossils found in the Asian region that meet certain requirements (as to skeleton and skull) which differ slightly from ergaster.
"Homo neaderthalensis" (usually called Neanderthal man) lived from about 250,000 to about 30,000 years ago. Also, less usual, as "Homo sapiens neanderthalensis": there is still some discussion if it was a separate species "Homo neanderthalensis", or a subspecies of "H. sapiens". While the debate remains unsettled, evidence from mitochondrial DNA and Y-chromosomal DNA sequencing indicates that little or no gene flow occurred between "H. neanderthalensis" and "H. sapiens", and, therefore, the two were separate species. In 1997, Dr. Mark Stoneking, then an associate professor of anthropology at Pennsylvania State University, stated:
More investigation of a second source of Neanderthal DNA supported these findings.
A genetic analysis of a piece of finger bone found in Siberia has produced a surprise result. It dates to about 40,000 years ago, at a time when Neanderthals and modern man were living in the area. German researchers found its mitochondrial DNA did not match either that of our species or that of Neanderthals. If this result is correct, the bone belongs to a previously unknown species. The degree of difference in the DNA suggests this species split off from our family tree about a million years ago, well before the split between our species and Neanderthals.
"Homo floresiensis", which lived about 100,000–12,000 years ago has been nicknamed "hobbit" for its small size. Its size may be a result of island dwarfism, the tendency for large mammals to evolve smaller forms on islands. "H. floresiensis" is intriguing both for its size and its age. It is a concrete example of a recent species of the genus "Homo" that shows derived traits not shared with modern humans. In other words, "H. floresiensis" share a common ancestor with modern humans, but split from the modern human lineage and followed a different 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 cm This is small for a chimpanzee and less than a third of the "H. sapiens" average of 1400 cm.
There is an ongoing debate over whether "H. floresiensis" is indeed a separate species. Some scientists believe that "H. floresiensis" was a modern "H. sapiens" suffering from pathological dwarfism. Modern humans who live on Flores, the island where the skeleton was found, are pygmies. This fact is consistent with either theory. One line of attack on "H. floresiensis" is that it was found with tools only associated with "H. sapiens".
Stone artifacts have been found on Flores which can be dated to a million years ago. These artifacts are "proxies"; which means there were no skeletons of humans, but only a species of "Homo" could have made them. The artifacts are flakes and other implements, 48 in all, some of which show signs of being worked to produce a cutting edge. This means that humans were present on Flores by that date, but it does not tell us which species that was.