New research suggests Homo erectus—the most successful hominin prior to the emergence of modern humans—reached southeast Asia later than is conventionally assumed. It’s a significant finding, as it casts doubt on a theory that points to an Asian birthplace for this now-extinct species.
Homo erectus reached the Indonesian island of Java at some point between 1.3 million to 1.5 million years ago, according to research published today in Science. That’s around 300,000 to 500,000 years later than the previous estimate, which was established by Rutgers archaeologist Carl Swisher in 1994. The revised time frame will help to reconcile inconsistencies in the archaeological record, and possibly clear up a longstanding debate about the geographical origin of this species.
Indonesia is hugely important for understanding human migration and settlement patterns in Asia during the Early Pleistocene, a period that ended around 780,000 years ago. Of all the archaeological sites in the region, however, perhaps none is more important than Sangiran, which is located on the island of Java. To date, over 100 different hominin fossils have been recovered at Sangiran, which has been designated as an UNESCO World Heritage Site.
Trouble is, Sangiran is located within a large volcanic dome, and it contains thick sedimentary deposits that reflect the region’s tumultuous geological history. Since 1936, archaeologists have dug out many bones from Sangiran’s rich sedimentary layers, but the dome’s complex geology has prevented scientists from establishing an iron-clad and accepted chronology. Shuji Matsu’ura, the first author of the new study and a researcher at Japan’s National Museum of Nature and Science, along with his colleagues, decided to take another look at Sangiran, resulting in the most comprehensive and credible dates yet for this exceptional site.
“It’s always good to see a reassessment of the chronology for an established site especially when the chronology has not been revisited for more than two decades,” Kira Westaway, a geochronologist at Macquarie University in Australia who wasn’t involved in the new study, told Gizmodo in an email.
The timing of this new study is intriguing, as research published just four weeks ago (co-authored by Westaway) offered new dates for the extinction of Homo erectus in Indonesia (and the world, for that matter), while the new paper is providing an updated time frame for their origins in the region. Together, the studies are vastly improving our understanding of H. erectus, a hominin that reigned for nearly 2 million years.
The unconvincing dating of the sediments within which these fossils were recovered has led to uncertainty and controversy, particularly as it pertains to the timing of H. erectus in southeast Asia. It’s crucially important that this be resolved, as it will finally settle a debate as to where H. erectus emerged as a species. Archaeological evidence suggests this species emerged in Africa, but the exceptionally old dates provided by Swisher led to the suggestion that Asia birthed this hominin, with Homo habilis likely representing its parent species (this theory is not as outlandish as it may appear, as a sister species to the Neanderthals, the Denisovans, likely emerged in Asia, although this happened many hundreds of thousands of years later).
Indeed, the older chronology has presented some big headaches for archaeologists, who have struggled to reconcile the presumed arrival dates to those documented elsewhere. Westaway pointed to two notable examples: the Dmanisi site in Georgia, dated at 1.8 million years ago, and the Koobi Fora site in Kenya, dated to 1.7 million years ago. These dates led Swisher “to claim an Asian birthplace for Homo erectus,” according to Westaway.
Previous attempts to date the complex volcanic materials at Sangiran relied on a lone dating technique, namely argon-argon dating of materials extracted from the pumice. As Westaway explained to Gizmodo, this resulted in “poor association” between the sediment and the fossils, while also producing the older chronology.
For the new study, Matsu’ura and his colleagues relied upon two different dating techniques, uranium-lead dating and fission-track dating, which they used to re-date the Sangiran sediment in and around the layers in which the fossils were found. By doing so, the researchers sought to “rectify the older versus younger chronology, and for the first time use two dating techniques that have never been applied to this site,” in which the uranium-lead technique was used to date volcanic zircon crystals and the fission-track technique to date the zircons, said Westaway. Together, these techniques “provide supporting age estimates because they constrain different events,” she said, namely the timing of volcanic events and the crystallization of old magma.
The new dates point to an earlier time frame, in which Homo erectus arrived to the region around 1.3 million years ago and definitely no earlier than 1.45 million years ago, according to the new research.
“This might not sound like a huge difference, but those 200,000 to 500,000 years swings the balance back to an African center of evolution for Homo erectus and helps to tie in the morphological changes seen between the younger and older hominins at Sangiran to a major climatic shift that occurred around 1.2 million years ago,” said Westaway.
Indeed, a cooling trend around this time significantly affected the planet’s biosphere and geography, and very possibly Homo erectus people, leading to some adaptive physical changes. Either that, or a separate population of H. erectus arrived to the region when the sea levels dropped and dry land connected the archipelago. Either way, the new dates fit in nicely with this narrative.
This latest research points to the benefits of re-visiting old archaeological sites. Discoveries should almost never be considered one-and-done projects, as emerging technologies can provide new ways of studying the past.