By Michael Marshall
Homo erectus reached Java later than we thought
Agoes Rudianto/Anadolu Agency/Getty Images
Ancient humans took hundreds of thousands of years to make the journey from mainland Eurasia to Indonesia, according to a new dating study, perhaps reaching Java half a million years later than we previously thought.
Homo erectus was one of the first species in our genus, Homo, and is thought to be our direct ancestor. The oldest fossils are about 2 million years old. While the species may have evolved in Africa, it is the oldest hominin known to have roamed beyond Africa.
H. erectus migrated across Asia within no more than a couple of hundred thousand years – remarkably fast given that hominins apparently failed to migrate so far over millions of years of earlier evolution. Fossils show it was in Georgia by 1.8 million years ago, in China before 1.6 million years ago and in Indonesia perhaps 1.7 or 1.8 million years ago.
However, this Indonesia date has been questioned in the past with some arguing H. erectus reached the islands of South-East Asia no earlier than 1.3 million years ago. To settle the debate, Shuji Matsuura of the National Museum of Nature and Science in Tsukuba City, Japan, and his colleagues re-examined the site of Sangiran on the island of Java, which has yielded over 100 hominin fossils.
The team took a closer look at the sediment layers in which the remains were found. Crucially, there were layers of volcanic ash within the pile of sediments. The team used two methods to date the volcanic material, constraining the ages of the surrounding sediments.
A best estimate for the first hominin colonisation into the Sangiran area is 1.3 million years ago, says Matsuura, with an upper limit of 1.5 million years. It is unclear why it took H. erectus so long to reach Indonesia, although if the species lacked seafaring skills that might go some way towards explaining the delay.
The study also gives more information about changes in the Sangiran H. erectus. So many fossils have been found in the various layers of dirt at the site that it is possible to track the way the species changed with time using Matsuura’s team’s revised site dates. This shows that by 0.9 million years ago, individuals had developed larger brains and different-shaped skulls.
Around this time, climate change led to a drastic fall in sea levels, exposing so much submerged land that Indonesia became connected to mainland Asia. This may have led to a flurry of new hominins into Indonesia, or driven a spurt of evolution among the local H. erectus.
Journal reference: Science , DOI: 10.1126/science.aau8556
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By Michael Marshall