Thor Heyerdahl made his voyage on the balsa raft in defense of a theory, the theory of the Pacific as a highway by which Peruvian men and ideas came to Polynesia. [Sea Routes to Polynesia is] a set of nine of his papers, mostly written in the 1960's, expounding and elaborating on this theme. His work on the curious multiple centerboards of the Incas that make balsa rafts such as Kon-Tiki capable of tacking and sailing into the wind, and his understanding of long sea voyages under plausible early circumstances, are fully convincing…. Heyerdahl argues that, whereas there are no good sea routes out of America across the Atlantic, there are plausible routes, one equatorial and one southerly, out of America toward Asia, and one "natural passage" from Indonesia north of Hawaii to Mexico, found by Spanish shipmasters in 1565. Much less compelling is the evidence that by such...