Great American Biological Interchange (image) Smithsonian Tropical Research Institute Share Print E-Mail Caption After the Isthmus of Panama formed, animals and plants could move back and forth between continents, the Great American Biological Interchange. Smithsonian scientists are debating when this happened. Credit Smithsonian Tropical Research Institute Usage Restrictions Credit STRI Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.