Interpretations of the Australian Paleoanthropological Evidence

Some of the Mungo individuals represent the oldest Australian human fossils so far discovered. It is one of these, Lake Mungo 3 (LM 3) (Figure 10.1), that has now been dated at either 60,000 years ago (Thorne et al., 1999) or 40,000 years ago (Bowler et al., 2003). They are described as having a high frontal and relatively thin cranial walls. The cranium is spherical in shape, the frontal lacks much of a supraorbital torus, and the face is relatively flat and lies immediately below the frontal (Webb, 1989). In other words, this early population is very modern in appearance.

Apart from LM 1, LM 3, and some other, much less complete, specimens from the Willandra Lakes, the main candidate for the status of "gracile" among the Australian fossils is the skull from Keilor (Melbourne Airport). Keilor, in particular, is said to resemble the cranium from Wajak in Java and some specimens from southern China — Ziyang, dated to around 38,000 years ago, and Liujiang, arguably dated at 67,000 years ago (see previous chapter). The isolated incisor teeth from Liujiang are "shovel-shaped" (Wu & Poirier, 1995), and this incisor morphology has often been argued to represent a regional trait linking Chinese H. erectus

Figure 10.1 ► Willandra hominin specimen 3 (Lake Mungo III) from southern New South Wales, Australia.

Hominin Crania

Figure 10.1 ► Willandra hominin specimen 3 (Lake Mungo III) from southern New South Wales, Australia.

(or Homo pekinensis, as we prefer — they differ consistently from the true Homo erectus from Java) and modern East Asians (Weidenreich, 1937). This feature, however, is also observed in Neanderthals, H. heidelbergen-sis, and even the presumed ancestral species Homo ergaster from Africa (e.g., WT-15000) and A. africanus. Thus it is simply a "primitive" feature for the hominins (see also Stringer et al., 1997). Note, too, that incisor shoveling is not strongly developed in Aboriginal Australians, including the Keilor skull, so if this "regional continuity" character were correct, it would be evidence against a China-Australia link, not for it!

The so-called "robust" Pleistocene Australians include skulls from Kow Swamp (Figure 10.2), Cohuna, and Coobool; all apparently date from about 9,000-12,000 years ago. They have large jaws and teeth, thick skull bones, prominent continuous brow ridges, and, in particular, flat, receding foreheads. Thorne (1976, 1977, 1984, 2000), Thorne and Wolpoff (1981), Wolpoff et al. (1984), and Wolpoff (1989) argue that these "robust" fossils all demonstrate a continuity of morphological features with Javanese Homo erectus and share no physical and/or genetic influence from the Pleistocene of Africa. Indeed, much of the entire multiregional scheme has been based on comparisons of early Pleistocene Indonesian H. erectus specimens from Sangiran and the Late Pleistocene Australian modern human fossils from Kow Swamp (Thorne, 1976; Thorne & Wolpoff, 1981).

Skull Image Heidelbergen
Figure 10.2 ► Kow Swamp 1 from Victoria, Australia. See text for details. Adapted from P. Brown (1981).

What of the other Australian fossils? One from the Willandra Lakes (WLH 50) is indeed very robust, and it has thicker skull bones than any from Kow Swamp (see Webb, 1989; Hawks et al., 2000); its date is 14,000 years ago. Hawks et al. (2000) have argued in depth that WLH 50 provides evidence, to them at least, for an H. erectus-Australian lineage. It has been argued, however, that the unusual cranial thickness and robusticity observed in WLH 50 are the results of a pathological condition associated with some form of hemoglobinopathy (Webb, 1995). Therefore, while Hawks et al. (2000) spend considerable time analyzing WLH 50 in terms of phenotypic and metric features, and while they themselves admit that they cannot rule out that WLH 50 may have suffered a pathological condition, they still maintain the continuity scheme. How seriously can we consider such a relationship when their evolutionary sequence from H. erectus to Australia is based on one specimen, especially one that is so problematic?

Another, from Cossack, Western Australia, is very large and appears to have a flat, receding forehead, but it is distorted and compressed, so it is difficult to interpret its actual morphological shape. Nitchie, from western New South Wales, is very much like Keilor but has larger brow ridges. This highlights a problem — the boundary between the two groups is far from clear-cut. Keilor, in fact, is every bit as large as any Kow Swamp, and it has an enormous palate. Lake Mungo 3 has thick skull bones and large teeth but is "gracile" in shape. Both are very different from the tiny LM 1, the only one that is really "gracile" at all.

As far as the dates go, the "graciles" appear earlier: Lake Mungo 1 and 3 are either 40,000 or 60,000 years old; Keilor is very latest Pleistocene (probably 10,000-20,000 years old). Of the "robusts," WLH 50 is 14,000 years old, the Kow Swamp specimens vary from 9,000 to 12,000 years ago, or alternatively 26,000 years ago (Stone and Cupper, 2003), and the Coobool skills vary about the same, while Nitchie (if it truly belongs to this group) is only 6,000 years old. If the Dihybrid model is correct, then the "graciles" arrived first and, the robusts much later.

P. Brown (1981, 1987, 1989, 1992), however, has argued that there is virtually no difference between the two types. A single origin for the first Australians is likely if one takes into account (1) temporal considerations, (2) sexual dimorphism, and (3) cultural practices, such as intentional cranial deformation. We will explain these three factors one by one.

First, there seems to be an increasing robusticity over time. We have already noted that the "graciles" came first. But this could mean either that a new ("robust") population did enter later or that there was gradual change toward greater robusticity, because until about 15,000 years ago the fossil record is very sparse. Antón and Weinstein (1999) were the first to draw attention to this trend in overall increased robusticity during the later Pleistocene fossil hominin record.

Second, there is sexual dimorphism. Webb (1989) adopted the Dihybrid model and at the same time classified them according to sex. Independently, both Pardoe (1991) and Groves (1990) examined these allocations and concluded that, if Webb had been right about sex, almost all his males were "robust" and almost all his females were "gracile." In other words, the criteria one uses to determine sex are the same as those to determine which of the two "types" one is examining!

Finally, there is artificial cranial deformation. This is a result of parents' deliberately or unintentionally altering their children's head shape in infancy; it is said to look more attractive, or it is culturally distinctive, or it may simply result from swaddling or other cradling practices. It has been very widespread throughout the world over time: Within the last few hundred years the Maya, the Aztec, some Plains Indians, some Hawaiians, the people of Espiritu Santo in Vanuatu, offshore islanders in Papua New Guinea, Lebanese Maronites and other Middle Easterners, and some women in the Toulouse region of France, all had artificially deformed crania. Usually these became long and flat, with very flat receding foreheads, though swaddling resulted in the opposite (short and high). P. Brown (1981) showed that the flat frontals observed in the Kow Swamp crania (Figure 10.3) are due to such intentional cranial deformation and so are not natural like those of H. erectus. Brown had analyzed crania from Arawe, on the island Melanesia, which are known to have been deliberately deformed, and compared them to crania from the Sepik River Region, known not to be affected by cranial deformation. He demonstrated that many of the "unique" features observed in the Australian "robust" crania are also present in the Arawe deformed specimens, including flattening of the frontal and occipital, an increase in cranial height, an increase in postorbital constriction, a well developed prebregmatic eminence, and a low position of maximum cranial breadth (P. Brown, 1981). Because there is no evidence that H. erectus was practicing intentional cranial deformation, this means that any similarity between it and Kow Swamp is purely superficial.

P. Brown (1981, 1987) then went on to examine some of the features used by Thorne and Wolpoff. He suggested that these supposed unique Australasian features are not unique. For example, while the Kow Swamp

Mechanical Means Cranial Deformation
Figure 10.3 ► Example of intentional cranial deformation, defined as a sloping forehead and anterior projecting lower face. See text for more details. Adapted from P. Brown (1981).

crania do show significant cranial thickness, Brown demonstrated that the thickness of the cranium observed in the female LM 1 is within the range observed in the Holocene female Murray Valley sample (P. Brown, 1987), while the male LM 3 specimen falls within the range of not only the male Murray Valley collection, but also the male Kow Swamp sample. Thus, again, the difference in cranial thickness between the robust and the gracile samples is not as distinct as some would have us believe.

It is appreciated, however, that intentional cranial deformation cannot alone explain all of the features said to be synapomorphies between the Indonesian and "robust" Australian fossil samples. The upper face of these groups is marked by well-developed supraorbital torus, a large postcanine dental complex, and large, robust mandibles. These characters will be the focus of the present discussion.

To date, many paleoanthropological studies have focused on pheno-typic comparisons of fossil samples, with little or no understanding of the functional and/or developmental processes that lie behind the formation of the morphologies being described and compared. This approach can be misleading, especially for those proposing any clade relationship between populations. For example, the multiregionalists base their model on morphological similarity between groups. This is acceptable if you can show that the morphological features being used are homologies. Such characters are phylogenetically significant because they help us identify past evolutionary relationships. For example, expanded frontal lobes associated with the anterosuperior location of the anterior cranial fossa are a phylogenetically significant feature linking all modern humans (see D.E. Lieberman, 1995, 2000). Homoplasy is the result of morphological convergence, parallelism, or reversal and not the result of immediate shared common ancestry, an example being a developed incisive canal in both modern humans and the orangutan. Such characters are of no phylo-genetic significance because they have evolved separately.

0 0

Post a comment