We continue with the series of blog posts, primitive man for children.
Immediate ancestors of the genus Homo
Hominid fossils were not discovered in Africa until the 1920s. In 1924, Raymond Dart described Australopithecus africanus. The specimen was called the Taung Child, an australopithecus infant discovered in a cave deposit being used for mining in Taung, South Africa. The remains consisted of a tiny, remarkably well-preserved skull and a cast of the individual's skull interior. Although the brain was small (410 cm³), its shape was rounded, unlike that of chimpanzees and gorillas, and very similar to a modern human brain. Furthermore, the specimen had short canine teeth, and the shape of its bones indicated that it was bipedal. All these features convinced Raymond Dart, who published the discovery, that the Taung Child was a bipedal human ancestor, a transitional form between apes and humans.
For a long time, Dart's claims were not taken seriously, until other similar skeletons were found. The prevailing view at the time was that brain growth preceded bipedalism. It was thought that high intelligence was necessary to be able to stand on two legs. This assertion turned out to be incorrect: bipedalism came first.
Australopithecus is now thought to predate the genus Homo, the group to which modern humans belong. Both Australopithecus and Homo sapiens are part of the tribe Hominini, but recent data have called into question the position of A. africanus as a direct ancestor of modern humans; it may well have been a cousin. Australopithecus was originally classified as either light or robust. The robust variety of Australopithecus has since been reclassified as Paranthropus, although it is still considered a subgenus of Australopithecus by some authors.
In the 1930s, when the robust specimens were first described, the genus Paranthropus was used. During the 1960s, the robust variety was moved to Australopithecus. The recent trend has returned to the original classification as a separate genus.
The genus Homo
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 may have been ancestors of H. sapiens. Many were probably our "cousins," having evolved far from our ancestral line.
Anthropologists continue to investigate the exact line of descent. A consensus on whether they should be considered separate species or subspecies has not yet been reached. In some cases, this is due to a scarcity of fossils; in others, it is due to the slight differences used to classify species within the genus Homo.
The evolution of the genus Homo took place primarily during the Pleistocene. The entire genus is characterized by the use of stone tools, initially crude, and increasingly sophisticated. So much so that in Archaeology and Anthropology the Pleistocene is often referred to as the Paleolithic, or the Stone Age.
Homo habilis
Homo habilis-2
A reconstruction of Homo habilis
Homo habilis was probably the first Homo species. It evolved from Australopithecus about 2.5 million years ago and lived until about 1.4 million years ago. It had smaller molars (back teeth) and larger brains than australopithecines.
Towards Homo erectus
There are two proposed species that lived from 1.9 to 1.6 million years ago. Their relationship 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 Homo 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 subspecies of H. erectus.
Homo ergaster and Homo erectus
Homo erectus was first discovered on the island of Java in Indonesia in 1891. The discoverer, Eugene Dubois, originally named it Pithecanthropus erectus based on its morphology, which he considered intermediate between that of humans and apes. Homo erectus lived from about 1.8 million to 70,000 years ago. Earlier specimens (from 1.8 to 1.2 million years ago) are sometimes considered a different species, or subspecies, called Homo ergaster, or Homo erectus ergaster.
In the Early Pleistocene, 1.5–1 million years ago, in Africa, Asia, and Europe, some populations of Homo habilis presumably developed larger brains and made more elaborate stone tools. These and other differences were sufficient for anthropologists to classify them as a new species, H. erectus. Furthermore, 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 opening in the skull where the spinal cord enters). They may have used fire to cook their meat.
A famous example of Homo erectus is Peking Man; others have been found in Asia (particularly 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 (regarding skeleton and skull) that differ slightly from ergaster.
Neanderthal Man
Neanderthal Reconstruction
Dermoplastic Reconstruction of a Neanderthal
Homo neanderthalensis (usually called Neanderthal man) lived from approximately 250,000 to about 30,000 years ago. Also, less commonly, Homo sapiens neanderthalensis: there is still some debate as to whether it was a separate species of Homo neanderthalensis or a subspecies of H. sapiens. While the debate remains unresolved, 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 associate professor of Anthropology at Pennsylvania State University, stated:
«"These results [based on mitochondrial DNA extracted from Neanderthal bone] indicate that Neanderthals did not contribute mitochondrial DNA to modern humans... Neanderthals are not our ancestors.".
Further research from a second source of Neanderthal DNA supported these findings.
A third species
A genetic analysis of a finger bone fragment found in Siberia has yielded a surprising result. Dating back some 40,000 years, to a time when Neanderthals and modern humans coexisted in the area, German researchers found that its mitochondrial DNA matched neither that of our species nor that of Neanderthals. If this result is correct, the bone belongs to a previously unknown species. The degree of DNA difference suggests that this species diverged from our family tree approximately one million years ago, long before the split between our species and Neanderthals.
Homo Floresiensis
Homo floresiensis, which lived between 100,000 and 12,000 years ago, has been nicknamed the hobbit because of its small size. Its small size may be the result of island dwarfism, the tendency of large mammals to develop smaller forms on islands. H. floresiensis is intriguing both for its size and its age. It is a prime 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 diverged from the modern human lineage and followed a different evolutionary path. The main find was a skeleton believed to be that of a woman around 30 years old. Discovered in 2003, it has been dated to approximately 18,000 years old. The living woman was estimated to be one meter tall, with a brain volume of only 380 cm3, which is small for a chimpanzee and less than a third of the average H. sapiens brain volume of 1400 cm3.
There is an ongoing debate about 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 living on Flores, the island where the skeleton was found, are pygmies. This fact is consistent with either theory. One line of attack against H. floresiensis is that it was found with tools only associated with H. sapiens.
Human arrival in Flores
Stone artifacts have now been found at Flores that can be dated to a million years ago. These artifacts are proxies; that is, there were no human skeletons present, but only one species of Homo could have made the artifacts. The artifacts are flakes and other implements, 48 in total, some of which show signs of being worked to produce an edge. This means that humans were present at Flores at that time, but it doesn't tell us which species.
Homo sapiens
Homo sapiens has existed from about 250,000 years ago to the present. Between 400,000 years ago and the second warm period of the Middle Pleistocene, around 250,000 years ago, their skulls grew larger and they developed more sophisticated technologies based on stone tools. One possibility is that a transition occurred between H. erectus and H. sapiens. Evidence from Java Man suggests an initial migration of H. erectus out of Africa. Then, much later, a new evolution of H. sapiens occurred, evolving from H. erectus in Africa. Subsequent migrations within and out of Africa eventually replaced the earlier H. erectus.
Outside of Africa
Homepage: outside of Africa
Studies of the human genome, especially Y-chromosome and mitochondrial DNA, have supported a recent African origin. Evidence from autosomal DNA also supports a recent African origin. The details of this great saga are not yet fully established, but by about 90,000 years ago, they had migrated to Eurasia and the Middle East. This was the area where Neanderthals, Homo neanderthalensis, had been living for a long time (at least 500,000 years in Western Europe).
Approximately 42,000 to 44,000 years ago, Homo sapiens arrived in Western Europe, including Great Britain. In Europe and Western Asia, Homo sapiens replaced Neanderthals around 35,000 years ago. The details of how this happened are unknown.
Around the same time, Homo sapiens arrived in Australia. Their arrival in the Americas was much later, about 15,000 years ago. All these earlier groups of modern humans were hunter-gatherers.
Current research has established that humans are genetically quite homogeneous (similar). The DNA of individuals is more alike than is usual for most species. This may have resulted from their relatively recent evolution or from the Toba catastrophe. Distinctive genetics have emerged as a result of small groups of people migrating to new environmental circumstances. These adaptive traits are a very small component of the Homo sapiens genome and include external "racial" characteristics such as skin color and nose shape, and internal characteristics such as the ability to breathe more efficiently at high altitudes.
H. sapiens idaltu, from Ethiopia, about 160,000 years ago, is a proposed subspecies. It is the oldest known anatomically modern human.
List of species
