Working to solve the evolutionary mystery behind how monkeys managed to jump continents, scientists believe that African monkeys rode floating islands across the Atlantic Ocean (about 1,000 miles at the time) around 40 million years ago. This same theory also explains how monkeys then made the jump from South America to Central America when there were at least 100 miles of sea between the two bodies of land. Quartz details exactly how the monkey-island riding works.

These voyages happened when long-eroded chunks of riverbank finally tore free from the shoreline and were swept out to sea, says Nathaniel Dominy, an anthropologist and evolutionary biologist at Dartmouth College. Trees helped make these floating shelves seaworthy. While snarls of roots held the island together, standing trees functioned as sails, pushing the islands across the ocean faster than currents alone could, says Dominy, who wasn’t affiliated with the Panama study. Their branches also harbored monkeys. And since these drifting slabs of intact forest were several soccer fields in size, they had enough monkey food to sustain their passengers on the long voyage.

Head over to Quartz to read more.

Feature image via Flickr user Lucius Kwok