An impossible crossing
In the Soa Basin on the Indonesian island of Flores, archaeologists have found simple stone tools—flakes and choppers—alongside the fossil remains of an extinct pygmy elephant called a Stegodon. Analysis of volcanic ash layers sandwiching these artifacts provides a startlingly old date: hominins were on this island at least 840,000 years ago, with some evidence pushing that to one million years. The hominin assumed to be responsible is Homo erectus, the only human species known to inhabit the region at that time.
This is a geographical puzzle. Flores is located east of the Wallace Line, a deep oceanic trench that separates the fauna of Asia from that of Australia. Named after naturalist Alfred Russel Wallace, this channel has never dried up. Even during ice ages when sea levels dropped by 120 meters and connected many islands to the mainland, a permanent water barrier isolated Flores. To reach the island, Homo erectus would have needed to cross a minimum of 25 kilometers of open ocean, likely with strong currents.
Deliberate mariners or accidental colonists?
The presence of these ancient tools challenges our understanding of the cognitive abilities of Homo erectus. One theory proposes an accidental crossing—a small group swept out to sea on a natural raft of vegetation during a tsunami or storm. The major problem with this hypothesis is the requirement for a viable breeding population. A single accidental landing is unlikely to establish a permanent colony. The continuous 900,000-year record of a hominin tool-making tradition on Flores suggests a more stable and successful colonization.
This suggests the more controversial conclusion: Homo erectus intentionally built watercraft. They would have were smart enough for planning and constructing vessels, probably simple bamboo rafts, to make deliberate crossings. This evidence of seafaring predates the arrival of Homo sapiens in the region by more than 700,000 years.
The long-term residents of the island are believed to be the ancestors of Homo floresiensis, the diminutive hominin species nicknamed the "Hobbit." Fossils from Mata Menge, dated to 700,000 years ago, show that the ancestors of Homo floresiensis were already small-bodied. The long evolutionary history of this isolated population, from the first toolmakers to the last "Hobbits" who vanished around 50,000 years ago, begins with that first impossible sea voyage.