What is the most likely meaning of the phrase “Cook and Tupaia closed the circle” at the end of the following passage (paragraph 4)?

Two centuries later a global network of geneticists analyzing DNA bread-crumb trails of modern human migration would prove Cook right: Tupaia’s ancestors had colonized the Pacific 2,300 years before. Their improbable migration across the Pacific continued a long eastward march that had begun in Africa 70,000 to 50,000 years earlier. Cook’s journey, meanwhile, continued a westward movement started by his own ancestors, who had left Africa around the same time Tupaia’s ancestors had. In meeting each other, Cook and Tupaia closed the circle, completing a journey their forebears had begun together, so many millennia before.

A. They established a close friendship that was unlikely because they were from such different cultures.

B. Their ancestors left Africa at the same time and migrated to different places, but more migration led Cook and Tupaia to be in the same spot.

C. Studying the DNA of Cook and Tupaia proved to geneticists that they were related.

D. They made a circular journey, stopping at all the major islands until they returned to Tahiti.