Raft

The raft is buoyancy recognized—the observation that some materials float and that lashing them together creates platforms capable of supporting human weight. This conceptual leap, requiring no tools more sophisticated than cordage, opened oceanic travel tens of thousands of years before boats were hollowed or planked.

The adjacent possible for rafts required only observation that wood floats and knowledge of lashing techniques. Both existed long before the first raft was built, suggesting the invention's late emergence (relative to its simple requirements) reflects not technological but geographical constraint: why build a raft without water worth crossing? The colonization of Australia around 65,000 years ago provides the first unambiguous evidence of watercraft—and the 90-kilometer sea crossing to Sahul required something to float on.

Rafts solve problems boats cannot. They draw almost no water, enabling navigation of shallows and rapids impassable to hulled vessels. They cannot swamp because they have no interior to fill. They can be constructed from whatever floats locally—logs, bamboo, reeds, inflated skins—without specialized tools or skills. This material flexibility ensured rafts appeared independently wherever humans met water.

The raft's limitations constrained its trajectory. Rafts are slow; they cannot sail efficiently against the wind; they absorb water and lose buoyancy over days. For these reasons, boats—hollowed or planked—eventually replaced rafts for most purposes. But rafts persisted in niche roles: river transport where draught matters, exploration where simplicity matters, and emergency where availability matters.

The Thor Heyerdahl expeditions demonstrated raft capability: Kon-Tiki crossed 6,900 kilometers of Pacific Ocean on balsa logs in 1947. While Heyerdahl's migration theories were wrong, his proof of raft seaworthiness was valid. Ancient rafts could have crossed any ocean given sufficient supplies—and may have, leaving no archaeological trace in the water or on distant shores.