Evidence that ancient sea faring Austronesians (Malayo-Polynesians) brought bananas & chickens to South America and Polynesian rats to North America, and that the Chumash natives of California may have derived sewn plank canoes from Hawaiians voyagers/traders. So far, no genetic evidence of mixing. Other articles of interest can be found at the Human Migrations yahoo group.
Coconuts and People Yahoo group discussion (chicken, sweet potato, bottle gourd):
Update Aug. 08: Further DNA testing appears to show that the fowl remains in South America were not unique to Polynesia, but were common throughout Eurasia.