Evolutionary History

What is the evolutionary history of Homo floresiensis and how does this impact upon what we know about our origins as a species?

While scientists have learned much about the evolutionary history of Homo floresiensis since its discovery, there is still a range of questions that remain unanswered. For instance, researchers continue to debate the evolutionary history that led to the Hobbit’s unique blend of skeletal features. If Homo floresiensis was a descendant of Homo erectus, then the modern-like limb proportions of Homo erectus must have evolved in Homo floresiensis to become more like those of earlier Homo and Australopithecus species, which had shorter legs and more robust upper limbs than Homo erectus. This shift may indicate a return to more arboreal behaviours or represent an outcome of island adaptation. An alternative proposition is that these primitive skeletal traits in Homo floresiensis reflect an ancestry in earlier Homo or Australopithecus groups, instead of the later Homo erectus. This second scenario is more radical, as it implies a currently unknown dispersal event of hominins before Homo erectus spread out of Africa. It is interesting to note that recently stone tools were found in southern China that have been dated at 2.1 million years ago, which is older than the earliest proven presence of Homo erectus in Asia at Dmanisi, where fossils of early Homo erectus have been dated at between 1.85 million- to 1.78-million year old. Although the stone tools from China do not reveal who their maker was, their early age does support the possibility that our genus left Africa before Homo erectus even had evolved, and that instead, an earlier hominin such as Homo habilis may have been the first to leave Africa.

Regardless of the explanation, more research is needed to bring greater clarity to the evolutionary history of Homo floresiensis. The lineage leading to the Hobbit may have evolved in isolation on Flores for more than a million years, as is suggested by dated stone tools found at the open site Wolo Sege at 80 km east of Liang Bua. A handful of teeth and a piece of mandible were excavated in 700,000-year-old layers at the site Mata Menge in the same sequence. The mandible fragment, which belonged to an adult individual, is even slightly smaller than the two Homo floresiensis mandibles, as are the isolated teeth from Mata Menge. These fossils have been attributed to the direct ancestor of Homo floresiensis, but as mentioned previously, they are separated by a gap of more than half a million years in time. It would be very helpful if more complete hominin fossils from the Early Pleistocene of Flores would turn up so that we can compare those fossils with LB1 and see if some of the characteristics of Hobbit evolved as a special adaptation to the insular environment, or were inherited from the island colonizing ancestral population.

To complicate the puzzle even further, the existence of another small-bodied insular hominin on the island Luzon was recently announced in the journal Nature. Dubbed as a separate species, Homo luzonensis, it is based on an upper tooth row and a few hand and foot bones, and lived on the Philippine island around the same time as Hobbit was living on Flores. Like on Flores, there is a much older record of hominin presence on Luzon, as evidenced by 700,000-year-old stone tools found associated with a butchered rhinoceros carcass from an open site. What was the relationship between these two hominins that are separated by almost 3000 km of islands and sea barriers? Did they evolve separately in isolation, or did the ancestral population of the Luzon hominins migrate southward to establish the Hobbit lineage on Flores?

The revised chronology for Homo floresiensis raises questions about the nature of any interaction between Homo floresiensis and modern humans, and whether our species played a role in the eventual disappearance of the Hobbit. In light of recent genetic research that has shown the presence of extinct hominin DNA (from Neanderthals and Denisovans) in some modern human populations, it begs the question of how Homo floresiensis is related genetically to modern humans and other extinct hominins, and if Homo floresiensis may have contributed to the genetic makeup of Homo sapiens through interbreeding. Unfortunately, the tropical environment of Flores does not favour the preservation of ancient DNA. That said, with the rapid development witnessed in recent palaeogenomic research, it is certainly possible that scientists might be able to characterise the genetic sequence of Homo floresiensis in the near future. Alternatively, paleoproteomics, the study of ancient proteins preserved in bone, may provide clues about the ancestry of Homo floresiensis. The extraction and analysis of ancient proteins from fossil bones is a rapidly developing discipline. Albeit with less resolution than with the study of ancient DNA, proteins tend to preserve better than DNA, and currently, proteomic studies are being tested on Homo floresiensis fossils.

At Liang Bua, the transition from the Pleistocene (associated mainly with Homo floresiensis) to the Holocene (associated exclusively with modern humans) is accompanied by a shift in the type of archaeological finds. As we discussed in week 3, a greater proportion of stone artefacts from the Holocene layers are produced on chert. The frequency of burning activities is also higher during the Holocene. Another example is that, while mollusc remains are largely absent in the Pleistocene deposits, the Holocene deposits contain notable accumulations of freshwater, marine and terrestrial mollusc shells. This observation suggests that mollusc collection was not part of the repertoire of Homo floresiensis activities at Liang Bua, whereas modern humans exploited molluscs, possibly for food and as material for making tools and ornaments, such as beads. Taken together, the dissimilarities between the cultural remains of the two hominin groups likely reflect evolutionary differences in aspects of their behaviour and use of resources, such as diet, mobility, technology, and even symbolism and communication. These differences may go some way to explaining the survival of our species and the extinction of the Hobbit.

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Homo Floresiensis Uncovered: The Science of ‘the Hobbit’

University of Wollongong

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