A multi-proxy approach to exploring Homo sapiens’ arrival, environments and adaptations in Southeast Asia

Abstract

The capability of Pleistocene hominins to successfully adapt to different types of tropical forested environments has long been debated. In order to investigate environmental changes in Southeast Asia during a critical period for the turnover of hominin species, we analysed palaeoenvironmental proxies from five late Middle to Late Pleistocene faunas. Human teeth discoveries have been reported at Duoi U’Oi, Vietnam (70–60 ka) and Nam Lot, Laos (86–72 ka). However, the use of palaeoproteomics allowed us to discard the latter, and, to date, no human remains older than ~ 70 ka are documented in the area. Our findings indicate that tropical rainforests were highly sensitive to climatic changes over that period, with significant fluctuations of the canopy forests. Locally, large-bodied faunas were resilient to these fluctuations until the cooling period of the Marine Isotope Stage 4 (MIS 4; 74–59 ka) that transformed the overall biotope. Then, under strong selective pressures, populations with new phenotypic characteristics emerged while some other species disappeared. We argue that this climate-driven shift offered new foraging opportunities for hominins in a novel rainforest environment and was most likely a key factor in the settlement and dispersal of our species during MIS 4 in SE Asia.

Early presence of Homo sapiens in Southeast Asia by 86–68 kyr at Tam Pà Ling, Northern Laos

“…In the time interval 70–33 kyr (TPLOSL 4 and TPLOSL 10) 37 , the carbon isotope composition (δ 13 C values) of mammalian teeth from TPL describes a forested habitat, with significant closed-canopy forests 75 . This is consistent with the environmental reconstruction of TPL based on snails 73 and with the assumption of the return of more forested conditions in the mid-Late Pleistocene 76 . Moreover, the δ 13 Cdiet values from two teeth of TPL 1 clearly highlights a strict reliance on dietary resources from a forest environment 75 .…”

A Middle Pleistocene Denisovan molar from the Annamite Chain of northern Laos

“…We recovered herbivores including Tapirus , Stegodon , and Rhinocerotidae, that were adapted to canopied woodlands in the area. We also found animals such as the Bos species, small-sized Caprinae and large-sized Cervidae (possibly Rusa unicolor ), which are all known to exhibit a great variability in their feeding behaviour and preferred habitats, from closed and intermediate forests to open grassland 33 .…”

Oxygen isotopes in orangutan teeth reveal recent and ancient climate variation

“…Our approach has the potential to contribute to reconstructions of ancient paleoenvironments in SE Asia based on studies of pollen, molluscs, faunal community compositions, guano records, and stable isotopes of teeth (e.g., Jablonski et al, 2000; Bird et al, 2005; Louys and Meijaard, 2010; Wurster et al, 2010; Hunt et al, 2012; Janssen et al, 2016; Stephens et al, 2016; Louys and Roberts, 2020; Bacon et al, 2021; Louys et al, 2022, in press). This may be especially timely given that recent work examining modern fauna compositions in African landscapes has cautioned that fossil herbivore assemblages tend to overestimate the extent of ancient grasslands in comparison to woodlands (Negash and Barr, 2023; also see Sokolowski et al 2023).…”