Australia: The Land Where Time Began
Origins - The Regional Continuity Hypothesis
There are 2 main theories for the origin of anatomically modern humans, the older proposed by Weidenreich, and later of Thorne and Wolpoff, is the regional continuity theory, the rapid replacement hypothesis, or out of Africa theory, is espoused by Stringer, and others.
According to the rapid replacement hypothesis of Stringer a single African origin of Homo sapiens occurred about 200 000 years ago. Since then the archaic people of areas outside Africa were replaced by successive waves of increasingly advanced peoples from Africa. The most recent wave of African migration, based on mitochondrial DNA analysis, proposes that a small group of modern humans left Africa about 70,000 BP, replacing all earlier populations throughout Eurasia and Australia, and eventually North and South America.
According to the regional continuity hypothesis, the already differentiated ancestral, archaic peoples had already spread from Africa, and further evolution occurred in several geographic regions. Australasia (Indonesia, New Guinea and Australia) is considered to be a key area for testing the latter because many physical anthropologists believe there is a link between H erectus - Java Man - and both prehistoric and modern Australians. Proof of regional continuity in this area would show that Homo sapiens sapiens evolved in the region, not by replacement from Africa. The main problem with finding proof either way is that the skeletal remains from Asia of the required age are very scarce, and what there is comes mainly from Java and China.
Some biologists do favour a combination of the 2 theories, migrations from Africa together with genetic assimilation of the older, more archaic pre-existing populations. All the known early hominids of Java are H erectus. Their brains were larger than their predecessors, and they made more sophisticated tools. The cranial capacity of the Sangiran H erectus was 950 ml compared to the average modern human capacity of 1300 ml. Early humans had brain capacities less than half this.
Until 1994 it was believed that the Sangiran remains were about 1 million years old. In 1994 Swisher and Curtiss published a paper in Science showing that they securely dated 2 Java sites to 1.8 million years, the same age as the oldest erectus remains in African. They dated the volcanic pumice associated with the skull of a young child at Modjokerto to 1.81 million +/- 40 000 years, and cranial remains from Sangiran to 1.66 million +/- 40 000 years. So there were erectus populations in at least 2 different parts of the world, Africa and Asia, living at the same time about 1.8 million years ago, before H sapiens had arisen. Did H erectus move out of Africa about 2 million years ago, about 600 000 years before the advanced Acheulean tools characterised by hand axes, stone cleavers and other bifacially-worked stone implements?
The complete absence of hand axes from Java, as well as all other known H erectus sites, has been a puzzle. Hand axes first appeared in Africa about 1.4 million years ago. If H erectus moved out of Africa prior to 1.4 million years ago they wouldn't have stone axes, it is unlikely they would forget how to make such useful tools. It has been suggested that it was actually an earlier ancestor of erectus that moved out of Africa, possibly H Habilis or even Australopithecus, but no evidence has been uncovered of either of these species in Asia.
Some don't accept the dates of Swisher and Curtis, preferring the estimated age for Sangiran of 700 000-1 000 000 BP.
The 11 Ngandong crania from Java are the youngest remains of H erectus, previously called H soloensis - Solo Man - found in a Late Pleistocene terrace on the Solo River. The skulls from Ngandong are large and broad, and have a capacity of 1150 ml. They were originally dated to 100 000 BP, but Swished has since unconfirmed dates of 50,000 BP for them. Ngandong is generally classed as very early H sapiens and is regarded by the proponents of the regional continuity theory as being the connection between the Javan Homo erectus and Homo sapiens.
In 1992 Thorne claimed that early Australian skeletons show the Java complex of features, along with braincase expansion and other more advanced features. Several dozen well preserved Late Pleistocene and Early Holocene skulls demonstrate the same combination of features that distinguished those Indonesian people from their contemporaries also distinguish living Australian Aborigines from other living peoples. A comment was made in 1965 concerning the Australian fossil skulls that "the mark of ancient Java is on all of them".
According to Thorne, the Javan features are 'thick skull bones, with strong continuous browridges forming an almost straight bar of bone across their eye sockets and a second, well-developed shelf of bone at the back of the skull for attachment of the neck muscles. Above and behind the brows, the forehead is flat and retreating. These early Indonesians [the Sangiran Homo erectus] also have large projecting faces with massive rounded cheekbones. Their teeth are the largest known in archaic humans from that time.' Other features are 'a rolled ridge on the lower edge of the eye sockets, a distinctive ridge on the cheekbone and a nasal floor that blends smoothly into the face'.
This 'unique morphology' was stable for at least 700 000 years in Java, according to Thorne, and is reflected in the Ngandong series of skulls, though their brain cases have evolved into the modern range. After Ngandong there is a serious gap in the Southeast Asian fossil record.
Philip Habgood has rigorously evaluated the morphological links between the Indonesian and Australian hominids and concluded that 'there are a number of morphological features which, when found in combination, appear to document continuity between the early Indonesian material and some prehistoric and modern Australian crania'. He cautions that 'the present skeletal sample from Australasia is not adequate to allow a clear distinction between the two competing explanations as to the origins of modern humans in the region'.
The 'stamp of early China' has also been identified by Thorne on the 'gracile' fossil group. Keilor and WLH 1 are claimed to closely resemble the Linkiang skull from southern China, the Zhoukoudian upper cave people, Niah from Borneo and Tabon from the Philippines.
Recently, the Jinniushan skull from China, an early form of homo sapiens, has been dated to 200 000 years ago. The age - ESR and uranium series dating is considered reliable, making it almost as old as some of the latest Chinese Homo erectus fossils, such as Skull V from the upper stratum of Zhoukoudian. Chen Tiemel and colleagues in Beijing commented 'This raises the possibility of the coexistence of the 2 species in China. The morphology of the skull suggests a strong local component of evolution, consonant with the "multi-regional continuity" model of the evolution of H sapiens'.
Thorne and Wolpoff stressed less parallels with China, less than with the Javanese affinities of the robust Australian hominids. Wolpoff wrote in 1980 'the resemblance of some specific characteristics to the morphology common in the Solo [Ngandong] sample that it is difficult to deny an evolutionary relationship in the Australasian region, a point suggested by Weidenreich several decades ago'.
The review of Sahul (Greater Australia) during the Pleistocene by Habgood & Franklin (2008) found no indication that the Package of cultural Innovations that had been suggested to have been taken from Africa with migrations that were suggested by the proponents of the 'Out of Africa' Hypothesis had reached Australia. The same applies to Southeast Asia, where there is no evidence of a 'package'.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|