What is the theme in Kon-Tiki: Across the Pacific by Raft by Thor Heyerdahl?

The capabilities of ancient humans is a recurring idea. Thor and crew prove that for long-distance sailing, fresh balsa logs tied together with ropes perform better than modern alternatives, such as chains instead of ropes and hulls instead of logs. The logs cannot develop holes from hitting a reef, as can a hull. The ropes shrink in the water and dig into the logs, thus protecting the ropes from wear. Steel chain cannot shrink in water and might pull apart in storms.