A 4000 year-old introduction of domestic pigs into the Philippine Archipelago: implications for understanding routes of human migration through Island Southeast Asia and Wallacea.

Introduction

Bellwood (1997, 2006) proposed that migrating farming communities from mainland China entered the Philippines via Taiwan between 4000 and 4500 years ago (Ka), bringing with them ground-stone technologies and pottery. Archaeological, bacterial and linguistic evidence suggest that these Austronesian-speaking peoples travelled onwards from the Philippines through Borneo in the west and Sulawesi to the south, eventually occupying the whole of Island Southeast Asia (ISEA), Melanesia and Oceania (Gray et al. 2009; Moodley et al. 2009). This hypothesis has been challenged by a number of archaeologists and geneticists who have argued that connections with mainland Southeast Asia, as opposed to Taiwan, are responsible for the Austronesian languages and agriculture in ISEA (Oppenheimer 1999; Solheim 2006). Solheim (2006), in particular, has argued for a strong similarity in Neolithic material culture between Vietnam and ISEA. Three domestic animals, the pig, dog and chicken, along with rats (commensals), all originated on the Asian mainland and are traditionally associated with the early farming communities of ISEA. They are commonly used as a proxy for identifying origins and routes of human migration in the past (Larson et al. 2005, 2007a, b & c; Liu et al. 2006; Matisoo-Smith 2007; Dobney et al. 2008). Reconstruction of human migration routes through ISEA using domestic pigs is based primarily on genetics, and relies almost exclusively on interpretation from modern population distributions. Based on these results, the earliest and most widespread domestic pigs introduced to ISEA are known as the 'Pacific Clade', and are believed to be the only lineage to have reached the Pacific islands in the company of colonising human populations. They appear to have originated somewhere in peninsular Southeast Asia and were transported through Malaysia, Sumatra, Java and islands in Wallacea (Flores, Timor, Moluccas) (Larson et al. 2005, 2007a & b; Dobney et al. 2008), thus adding some support to Solheim's claims for a Vietnam/ISEA connection.

There are difficulties in differentiating domesticated Sus scrofa from the wild progenitor and other close relatives such as the S. verrucosis/scrofa groups in the ISEA archaeological record. The only securely dated domesticated suid bones come from islands outside the natural range of these taxa, such as Flores, where they were possibly introduced between 3500 and 4000 years ago (Dobney et al. 2008; van den Bergh et al. in press), in the northern Moluccas at 3500 cal BP (Kayoa Island: Bellwood & White 2005), and in Lapita sites in Melanesia from around 3300 cal BP (Summerhayes 2007). A second lineage of modern domestic pigs identified in the Philippines appear to have a very different origin in East Asia (China), and were transported via Taiwan into the Philippine Archipelago, and then on to Micronesia (Larson et al. 2007a & b; Dobney et al. 2008). In the absence of any archaeological evidence to indicate the timing of domestic pig introduction to the Philippines, Dobney et al. (2008) suggested that this human-mediated dispersal was probably later than the translocation of the 'Pacific Clade' of pigs from the mainland to Australasia and the Pacific.

Recent excavations at the site of Nagsabaran on the northern Philippine island of Luzon have produced a small but significant bone assemblage dating to the Neolithic and Metal Age. The human-derived bone accumulations contained the native brown deer Cervus mariannus along with fish, mostly Sparidae, turtle and two different species of pig (Piper et al. 2009). One species was identified as a domesticate Sus scrofalverrucosus and directly radiocarbon dated using a single fourth premolar to 4500-4200 cal BP. This new evidence from Nagsabaran suggests that domestic pigs were possibly introduced from Taiwan to the northern Philippines prior to the translocation of the 'Pacific Clade' from the mainland through ISEA, Wallacea and on to Australasia and the Pacific. This in turn has implications for our understanding of the timing of suid introductions and human migrations from the mainland into Island Southeast Asia.

Archaeological background

The archaeological site of Nagsabaran consists of a large shell midden overlying alluvial deposits located on the south bank of the Zabaran Creek (or Nagsabaran Creek), close to where it joins the Cagayan River from the west, about 22km upstream from the Cagayan River mouth in Barangay Alaguia, Lal-lo, in the north of Luzon Island, Philippines (Figure 1). Bordered to the north by the Nagsabaran Creek and wet rice fields to the south, the Nagsabaran shell midden is an isolated, island-like formation in the alluvial plain, about 600m long, 100m wide and with a maximum depth of 3m (Figure 2A). Shells recovered in 1996 returned a [sup.14]C date of 2950 [+ or -] 90 BP (see Tsang et al. 2002; Hung 2008). A further eight test pits dug by a Filipino-Taiwanese team in 2000 and 2001 produced large numbers of artefacts including pottery, stone flakes, clay penannular earrings, other ornaments of bone, tooth and shell, and glass and stone beads. Based on the stratigraphic sequence uncovered, the site could be divided into two separate depositional sequences: an upper Metal Age horizon of deep shell midden characterised by blackish and reddish-brown ceramics and glass beads and bracelets, overlying Neolithic alluvial silt deposits with redslipped pottery, clay penannular earrings and a bracelet of Taiwan nephrite (Hung 2005, 2008; Iizuka & Hung 2005). A suite of 20 radiocarbon dates (18 charcoal, one river shell and one animal bone) showed that the date range for the shell midden at the 2-sigma outer limit is between 2100 cal BP and 1500 cal BP, whereas the silt layers are dated at the outer range to between 4000/3800 cal BP and 2600 cal BP (Hung 2008). During the mid--late Holocene it is estimated that the Cagayan River was at least 1m higher than its current level, and it was only after 2000 cal BP, when the water level subsided, that the shell middens accumulated along the banks of the river (Mijares 2007). It is therefore possible that some of the postholes identified at Nagsabaran represent the remnants of raised-floor Neolithic structures that extended out over the shallow margins of the river (Armand Mijares pers.camm.).

In order to better understand the cultural sequences of the last 4000 years in the Cagayan Valley, a third collaborative season of archaeological investigation was conducted at Nagsabaran, between the Australian National University and the National Museum of the Philippines, during November and December 2004. The excavations, located close to the edge of the mound, consisted of one 4 x 4m square (Pit 9) and one 2 x 4m rectangle (Pit 10), both dug to a depth of ~2.5m. The stratification was very similar to other shell midden sites in the Cagayan Valley, with a ~1m thick upper layer of shell midden (shallower towards the edges of the mound) overlying three distinctive alluvial layers that are collectively about 1m in depth (Hung 2008). The alluvial layers were cut by numerous postholes and burial pits, many from the Metal Age shell midden above (Figure 2B).

The results of the investigation confirmed interpretations in earlier studies and identified marked differences in the occurrences of different types of cultural material from the shell midden and underlying silts. For example, the shell midden contained a pottery assemblage with a high proportion of blackish and reddish-brown sherds in association with glass beads and bracelets, iron tools, jar burials and headless extended inhumations. The underlying alluvial silts on the other hand contained red-slipped sherds, coarse buff or beige sherds, spindle whorls, fired clay penannular earrings and pendants, and stone flakes and adzes, material that is well paralleled in Taiwan. The transition between the shell midden and underlying silts was clearly defined by a brief period of abandonment of the site (Layer 2 in Figure 2B).

[FIGURE 1 OMITTED]

The animal bones from Nagsabaran

In total, Pits 9 and 10 at Nagsabaran produced 1191 fragments of bone and tooth. The stratigraphic distribution of the animal bones recovered from the excavations corresponds well with the peaks in sherd concentrations identified by Hung (2008), indicating the two major phases in human activity at the site. The younger bone assemblage of 802 fragments (67 per cent of the total assemblage) is inter-mixed with the large shell midden and is located at depths from close to the modern surface to ~0.8m below modern ground (bmg) level. The oldest and deepest bone accumulation consists of just 389 (33 per ceno pieces and is located within the silty clay sediments between ~1.10 and 1.50m bmg. The taphonomic history of the bone assemblages are detailed in Piper et al. (2009).

Both phases of activity on the site contained a similar suite of vertebrate taxa that included deer and fish (Piper et al. 2008). By far the most common large mammal in the archaeological record, however, was the pig, accounting for c. 75 per cent (227) of all identifiable mammal fragments. The pig occurs throughout the stratigraphic sequence, from the upper 50mm to a depth of 1.60m in Pit 9, the latter corresponding to a potential age of ~4000 BP (see Hung 2008).

Morphometric analyses clearly indicated that two different pig taxa were present within the archaeological assemblage, easily differentiated by the size and morphology of their teeth as the endemic Philippine warty pig Sus philippensis and an introduced member of the Sus scrofa/verrucosus group (see accompanying technical note online at http://antiquity.ac.uk/projgall/piper/). Direct [sup.14]C dating of a lower fourth premolar from the introduced domestic pig species produced a date of 3940 [+ or -] 40 BP (WK23397 [uncal]) of 4500-4200 cal BP (OxCal Version 3), supporting dates obtained on charcoal from the same stratigraphic horizon, and the typological chronology of associated artefacts.

[FIGURE 2 OMITTED]

Discussion

The only large mammal taxa acquired by the Neolithic and Metal Age occupants at Nagsabaran appear to have been deer and pigs (although the skull of a large bovid was recovered from the lower layer in Pit 1, associated with red-slipped pottery, during the excavation of 2001). The paucity of large-bodied fauna is related to Luzon's isolated biogeographic location within the Wallacean group of islands (see Heaney 1985). From the small sample of dental elements recovered, it appears that teeth of wild pigs and deer slightly outnumber those of the introduced domestic pig. This would suggest that wild game contributed the greatest amount of protein (excluding the shellfish in the Metal Age) to the diet during both periods of occupation at Nagsabaran. However, in ISEA (as with many locations) we must be careful not to assign importance to a particular 'resource' from its abundance and frequency in the archaeological record alone. Many indigenous human populations in the islands differentiate between wild pigs used for general eating purposes, and domestic pigs kept specifically for ritual and ceremonial functions (Piper personal observation; see also Hayden 2003 and Barker 2007 for discussion). A less frequent slaughtering of domestic pigs is likely to make their remains less abundant in the archaeological record but may mask their overall social and ideological importance.

The discovery of domestic pig bones dated to before 4000 BP in the Philippines has important implications for our understanding of the introduction of suids across ISEA. Dobney et al. (2008) have shown fairly convincingly that the 'Pacific Clade' of pigs was introduced by migrating human populations to New Guinea and the Pacific Islands from the mainland somewhere in the Vietnam region via a route through peninsula Malaysia, Sumatra, Java and the Lesser Sunda Chain. They further argued that the complete absence of the 'Pacific Clade' haplotypes in pig samples from China, Taiwan and the Philippines suggested that if Neolithic peoples entered Island Southeast Asia via this route, as traditionally proposed by the 'Out-of-Taiwan' Model, then it is unlikely that they transported pigs with them (Larson et al. 2007; Dobney et al. 2008). Referring to the same genetic studies, Dobney et al. (2008: 70) suggest that a separate, probably later, human-mediated dispersal involved other mainland East Asian domestic pigs moving through the Philippines to Micronesia'.

The discovery of pigs at Nagsabaran demonstrates conclusively that domestic pigs were in fact introduced to the Philippines by at least 4000 cal BP. These conclusions are supported by associated material culture that has strong parallels with southern and south-eastern Taiwan, the proposed origin of the Neolithic populations in the Philippines and the rest of ISEA, Melanesia and the Pacific (Bellwood 2006; Hung 2008). This provides a robust indication that domestic pigs were introduced from China via Taiwan with the earliest evidence of Neolithic cultures. Intriguingly, the origins of the earliest domestic pigs on the key island of Sulawesi, south of the Philippines and east of Borneo, still appear to be unresolved. Neither the Taiwan/Philippines nor 'Pacific Clade' haplotypes reported by Larson et al. (2005, 2007a) appear to be present. Ancient mtDNA analysis has shown that the native Sulawesi warty pig Sus celebensis occurs on another Wallacean island, Flores, by approximately 7000 BP (based on associated charcoal dates) but there is, as yet, no clear evidence of whether this represents the translocation of wild pigs, or animals domesticated in Sulawesi in the early Holocene as suggested by Groves (1983) (see also Dobney et al. 2008 and van den Bergh et al. in press). Sulawesi has some of the earliest known 'Neolithic' sites in ISEA (Bellwood 1997) and a material culture that strongly resembles those identified in the Philippine Archipelago (Simanjuntak et al. 2008), yet, on current evidence, people did not introduce domestic pigs from either direction to the island with other forms of Neolithic material culture. Possibly, if S. celebensis was not already domesticated, it was domesticated locally during the Neolithic transition.

In Borneo, genetic evidence from modern domestic pigs suggests that they were either domesticated independently on the island, or females of native wild S. barbatus were crossed with domestic S. scrofa introduced from the mainland (Larson et al. 2007a). Either way, the genetic data imply that they are distinctive from both the 'Pacific Clade' and those from Taiwan and the Philippines. The oldest domestic pig from Borneo currently consists of the remains of a single individual from Megala Cave, mouth E (close to Niah Cave) and dates to ~3200 BP (Medway 1973; Cucchi et al. 2009). The [sup.14]C date, however, was taken on human skeletal remains and must therefore be treated with some caution. Nevertheless, a domestic or managed pig population which dates to the late third millennium BP has been identified in the Gan Kira entrance to the Niah Cave complex where they appear to have been integrated into pre-existing foraging systems (Piper unpubl. data). The Borneo and Sulawesi examples raise the question of whether the earliest human populations migrating through the islands of Southeast Asia necessarily transported domesticated animals during first colonisation events or that in some cases local domestication preceded introduction.

Conclusion

The results of the integrated zooarchaeological, morphometric and genetic studies discussed here suggest that the acquisitions and/or local domestication of pigs in the Island Southeast Asian region have been complicated processes. Certainly, if our interpretations stand up to further research and scrutiny, it appears that Neolithic peoples with connections to Taiwan introduced domesticated pigs to the northern Philippines during the late fifth/early fourth millennium BP with other parts of a Neolithic material culture. A second more extensive translocation of domesticated pigs ('Pacific Clade') entered ISEA through Sumatra and Java reaching the Lesser Sunda Chain between 4000 BP and 3500 BP. Further populations were possibly domesticated independently in Borneo and Sulawesi at currently unknown dates.

The pitfalls of relying primarily on modern genetics has recently been exposed in combined modern DNA and aDNA studies on the origins of European and Near Eastern pigs (Larson et al. 2007c). These studies identified ancient genetic lineages in archaeological samples within geographic regions where they no longer exist, completely changing our understandings of human migratory patterns and ideas on independent regional domestication. The Philippine and European examples demonstrate that the only way to identify the origins and lineages of ancient domestic animals in order to make inferences about former routes of human migration and interaction is through genetic research and zooarchaeological studies carried out in combination.

Acknowledgements

The authors would like to thank the National Museum of the Philippines for permitting access to the archaeological assemblages from Nagsabaran and granting permission to sacrifice the fourth premolar for radiocarbon dating. We are extremely grateful to Larry Heaney and colleagues at the Field Museum of Natural History, Chicago, for permission to access comparative material in their care, and for providing data and images on the modero Sus scrofa from Laos and the S. philippensis from Zamboanga used in this study. We are also grateful to Armand Mijares (University of the Philippines), Terry O'Connor (University of York) and the Earl of Cranbrook for reading early drafts of this paper or versions of the unpublished report it is based upon. Many thanks also to Jonathan Jacar of the National Museum of the Philippines who patiently produced the replicas of the pig premolar before its submission for radiocarbon dating. Dr Philip Piper would like to thank the OFfice of the Vice Chancellor for Research and Development (OVCRD), University of the Philippines for funding this research project. Hsiao-chun Hung thanks the Australian National University for supporting her PhD research at Nagsabaran.

Received: 20 November 2008; Revised: 10 March 2009; Accepted: 2 April 2009

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Philip J. Piper (1), Hsiao-chun Hung (2), Fredeliza Z. Campos (1), Peter Bellwood (3) & Rey Santiago (4)

(1)Archaeological Studies Program, University of the Philippines, Diliman, Quezon City 1101, Philippines

(2) Research Center of Humanities and Social Sciences, Academia Sinica, Taipei, Taiwan

(3) School of Archaeology and Anthropology, A.D. Hope Building 14, The Australian National University, Canberra, ACT 0200, Australia

(4) Archaeology Division, National Museum of the Philippines, Padre Burgos St., Manila 1000, Philippines