The Flores man (Homo floresiensis)

Taxonomy

Homo floresiensis is a small species of Hominid discovered in 2003 and subsequently described in 2004 (3). Generally assigned to the genus Homo, it is joined in this genus by host of other species including the Late Pleistocene Homo neanderthalensis, Homo erectus, and our own species: Homo sapiens. The etymology of the species is literally ‘Flores man’ (3).

H. floresiensis evolved from an ancestral population of hominids that arrived on Flores earlier (3), probably around a million years ago (5). Generally, the favoured ancestor is Homo erectus, as we have ample evidence of this species in Asia around the origin of Homo floresiensis, including findings from nearby Java. Another prominent hypothesis is that Homo floresiensis descended from a smaller, more primitive stock of hominids, similar to Homo habilis or even Australopithecus, though none of these are known from the region (17). Despite the geographic impracticalities, this hypothesis is not without support, morphological analyses have suggested affinities to early Homo species like Homo habilis, with phylogenetic analyses retrieving it as a sister group either to H. habilis or an outgroup to all other species of Homo (1, 2).

An additional pervasive hypothesis has been that Homo floresiensis does not constitute a valid species at all but can be assigned to Homo sapiens afflicted with Microcephaly, certain types of which cause not just decreased skull size but also overall body size (1). Alternatively, H. floresiensis may constitute a population of exceptionally small pygmies, which is not an unprecedented suggestion considering the prominence of pygmies in South-East Asia (16). However, morphological analysis of archaeological remains suggests that neither microcephalic human nor pygmoid remains do cluster with the fossil from Flores, and thus Homo floresiensis can be quite confidently be considered separate from modern humans (1).

The appearance of another similar dwarf hominid from the Late Pleistocene of the Philippines called Homo luzonensis (9) is also very interesting, and perhaps with further finds from the region more can be inferred about the relationships between these two species and a potential mutual progenitor.

In addition to the question of which ancestor gave rise to Homo floresiensis, we also should wonder how this species arrived on Flores. Two possible scenarios are postulated by Dennell et al 2014, the first is an arrival via island hopping from the other Lesser Sunda islands on very simple sea vessels, the hardest crossing of which would be the Lombok strait, which although narrow is notoriously treacherous (8). Maritime capabilities in hominids during the Early Pleistocene are highly contentious, it should be noted that seafaring vessels would be composed of materials that do not preserve well. The prevalence of hominids in the lesser Sundas, Philippine archipelago and various islands outside of South-East Asia during the middle Pleistocene as well as the reliance on marine resources of some communities of non-Human hominids certainly leaves the possibility open (11). The other hypothesis, favoured by Dennell et al 2014 is that the ancestors arrived via unintentional rafting, washed out on trees and debris from tsunamis (8). In this case, two additional source locations should be considered, Sulawesi and Kalimantan which given the prevailing currents make for more plausible rafting sources (8). The absence of hominid remains from Sumba is a weakness of the rafting hypothesis as this island should be more easily accessible with the southwards current from Flores (11).

Distribution and Age

The Flores man is known solely from its namesake Island of Flores in the Lesser Sunda Islands, exclusively at the sites of Liang Bua (3) and Mata Menga (6) and only from the Pleistocene. Initial remains were dated to about 18,000 years ago (3), additional fossils and tools associated with H. floresiensis have been found in a stratum dated to about 12,000 years ago (4, 15) both at Liang Bua. It should be noted however that a subsequent study conducted at the site of Liang Bua revised the age of the site and by extension the H. floresiensis remains to about 50,000 years ago (18), placing their terminal date substantially earlier.

The oldest known hominid fossils are known from Flores date to about 700kya and belong to a specimen very similar to the Late Pleistocene individuals and can be quite confidently assigned to Homo floresiensis (6, 17). Tools attributed to H. floresiensis are also known from this time (6). It is notable that earlier tools from around a million years ago are significantly different, placing a possible ceiling on the origin date for the taxon (5).

Ecology and Morphology

Homo floresiensis has often been dubbed as ‘hobbits’ due to their remarkably small stature, standing at only about a meter in height and weighing between 16 and 36kg, it is smaller than even the earliest hominids (3). The evolution of the tiny body size is traditionally considered a result of insular dwarfism, the reduced size allows the Flores men to support a viable population on a relatively small island (3). Alternatively, the species could be an example of pygmyism in a non-Human hominid species. Pygmyism is still not fully understood, but it seems to arise commonly in tropical rainforests (a habitat type that covers much of Flores today) and maybe a function of resource scarcity, high mortality, mobility needs, or even thermoregulation (16)

The cranial volume of the species is small, even when compared to early Australopithecus. Even when looking at the encephalization quotient (EQ), that is the relative brain size compared to body mass, the Flores men is at high estimates comparable to H. erectus and H. habilis and at lower estimates similar to the australopithecines (3). Nevertheless, despite this potential shrinking, the structure is similar (though not identical) to that of Homo erectus (10).

In terms of other morphological traits, H. floresiensis exhibits both traits relatively primitive to the genus Homo as well as a number of derived features. The teeth morphology, for example, is quite reminiscent of both H. sapiens and H. erectus, but tooth roots resemble Australopithecus and primitive members of Homo (15). The skull morphology on the other hand is quite suggestive of a more advanced species Homo (15)

The limbs are relatively robust and bear a stronger resemblance to Australopithecus afarensis than either Homo sapiens or Homo erectus (15). The feet of the Flores men were highly irregular, despite showing structural affinities to other hominids, they had dimensions more similar to those of the bonobo (Pan paniscus) and chimpanzee (Pan troglodytes). H. floresiensis is clearly bipedal based on the rest of the skeleton, therefore this is a puzzling result as the feet aren’t well suited for endurance running or sprinting (12).

H. floresiensis is associated with basic stone artifacts made from flakes of various types of rock, some have also been secondarily sharpened, a few even into points (4). Interestingly, there seems little difference between stone tools associated with 700-840kya deposits and the more recent artifacts from 95-74kya and 12kya (4). A single site dated to about a million years ago shows an Acheulean pick, a more complex tool that is not found in later deposits, this is possibly associated with Homo erectus (5, 6).

The Middle Pleistocene habitat in which the Flores man inhabited appears to have been a dry, savannah-like habitat with wetland areas present (6), this is of course in the fossil-bearing lowlands, it is unclear if H. floresiensis was found on the mountain slopes. This is inferred both from pollen studies as well as the presence of waterfowl and freshwater crocodiles in Flores (6).

Though the diet of H. floresiensis is still unclear, the structure of the teeth and jaw, as well as wear marks are consistent with the physical strain associated with chewing raw flesh (7). We have no evidence of direct results of hunting by these small hominids, however, it seems probable that their diet consisted in large part of the various large murids such as Komodomys, Paulamys, and Papagomys. Whether Homo floresiensis was capable of tackling and consuming larger prey is unclear. It seems unlikely they hunted the much larger dwarf stegodonts (Stegodon sondaari & Stegodon florensis), but perhaps they played a role in the extinction of the Flores giant tortoise (Collossochelys azizi/Megalochelys sp.) during the middle Pleistocene. As for potential predators, the Komodo dragon (Varanus komodoensis) and crocodiles of unclear taxonomic status, constituted the largest carnivores on Flores. In addition, the giant flightless stork Leptoptilos robustus reached sizes almost twice those of the modern marabou stork (13), if the diet was similar to its modern counterpart it probably did not feed on the Flores men directly but may, along with a local species of vulture, (Trigonoceps sp.) (14) have usurped carrion.

References

1.       Argue, D., Donlon, D., Groves, C., Wright, R.. (2006). Homo floresiensis: Microcephalic pygmoid, Australopithecus or Homo? Journal of Human Evolution 51(4), 360-374.

2.       Argue, D., Groves, C. P., Lee, M. S. Y., Jungers, W. L.. (2017). The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters. Journal of Human Evolution 107, 107-133.

3.       Brown, P., Sutikna, T., Morwood, M. J., Soejono, R. P., Jatmiko, Saptomo, E. W., Due, R. A.. (2004). A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431.

4.       Brumm, A., Aziz, F., van den Bergh, G. D., Morwood, M. J., Moore, M. W., Kurniawan, I., Hobbs, D. R., Fullagar, R.. (2006). Early stone technology on Flores and its implications for Homo floresiensis. Nature Letters 441. 624-628.

5.       Brumm, A., Jensen, G. M., van den Bergh, G. D., Morwood, M. J., Kurniawan, I., Aziz, F., Storey, M.. (2010). Hominins on Flores, Indonesia, by one million years ago. Nature Letters 464, 748-752.

6.       Brumm, A., van den Bergh, G. D., Storey, M., Kurniawan, I., Alloway, B. V., Setiawan, R., Setiyabudi, E., Grun, R., Moore, M. W., Yurnaldi, D., Puspaningrum, M. R., Wibowo, U. P.., Insani, H., Sutisna, I., Westgate, J. A., Pearce, N. J. G., Duval, M., Meijer, H. J. M., Aziz, F., Sutikna, T., van der Kaars, S., Flude, S., Morwood, M. J.. (2016). Age and context of the oldest known hominin fossils from Flores. Nature 524, 249-253.

7.       Cook, R. W., Vazzana, A., Sorrentino, R., Benzzai, S., Smith, A. L., Strait, D. S., Ledogar, J. A.. (2021). The Cranial biomechanics and feeding performance of Homo floresiensis. Interface focus 11.

8.       Dennel, R., Louys, J., O’Regan, H. J., Wilkinson, D. M.. (2014). The origins and persistence of Homo floresiensis on Flores: biogeographical and ecological perspectives. Quarternary Science Reviews 96, 98-107.

9.       Detroit, F., Mijares, A. S., Corny, J., Daver, G., Zanolli, C., Dizon, E., Robles, E., Grun, R., Piper, P. J.. (2019). A new species of Homo from the Late Pleistocene of the Philippines. Nature 568, 181-186.

10.   Falk, D., Hildebolt, C., Smith, K., Morwood, M. J., Sutikna, T., Brown, P., Jatmiko., Saptomo, E. W., Brundsen, B., Prior, F.. (2005). The Brain of LB1, Homo floresiensis. Science 398(5719), 242-245.

11.   Gaffney, D.. (2021). Pleistocene Water Crossings and Adaptive Flexibility Within the Homo genus. Journal of Archaeological Research 29, 255-326.

12.   Junger, W. L., Harcourt-Smith, W. E. H., Wunderlich, M. W., Tocheri, M. W., Larson, S. G., Sutikna, T., Due, A. D., Morwood, M. J.. (2009). The foot of Homo floresiensis. Nature letters 459, 81-84.

13.   Meijer, H. J. M., Due, R. A.. (2010). A new species of giant marabou stork (Aves: Ciconiiformes) from the Pleistocene of Liang Bua, Flores (Indonesia). Zoological Journal of the Linnean Society 160, 707-724.

14.   Meijer, H. J. M., Sutikna, T., Saptomo, E. W., Due, R. A., Jatmiko, Wasisto, S., James, H. F., Morwood, M. J., Tocheri, M. W.. (2013).

15.   Morwood, M. J., Brown, P., Jatmiko, Sutikna, T., Saptomo, E. W., Westaway, K. E., Due, R. A., Roberts, R. G., Maeda, T., Wasisto, S., Djubiantono, T.. (2005). Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia. Nature letters 437, 1012-1017.

16.   Perry, G. H., Dominy, N. J.. (2009). Evolution of the human pygmy phenotype. Trends in Ecology & Evolution 24(4), 218-225.

17.   Van den Bergh, G. D., Kaifu, Y., Kurniawan, I., Kono, R. T., Brumm, A., Setiyabudi, E., Aziz, F., Morwood, M. J.. (2016). Homo floresiensis–like fossils from the early middle Pleistocene of Flores. Nature letters 534, 245-248.

18.   Sutikna, T., Tocheri, M. W., Morwood, M. J., Saptomo, E. W., Jatmiko, Awe, R. D., Wasisto, S., Westaway, K. E., Aubert, M., Li, B., Zhao, J-X., Storey, M., Alloway, B. V., Morley, M. W., Meijer, H. J. M., van den Bergh, G. D., Grun, R., Dosseto, A., Brumm, A., Jungers, W. L., Roberts, R. G.. (2016). Revised stratigraphy and chronology for Homo floresiensis at Liang Bua in Indonesia. Nature 532, 366-369.