Scientists on Thursday announced the discovery of a “mother lode” of half dozen primate fossils in southern China. The discovery is likely to help researchers glean a deeper understanding of a longstanding evolutionary mystery — why did our species emerge in Africa when our ancestors originated in Asia?

“This has always been an enigma,” University of Kansas paleontologist K. Christopher Beard said, co-author of a paper published in the journal Science, said in a statement.  “We had a lot of evidence previously that the earliest anthropoids originated in Asia. At some point, later in the Eocene, these Asian anthropoids got to Africa and started to diversify there. At some point, the geographic focal point of anthropoid evolution — monkeys, apes and humans — shifted from Asia to Africa. But we never understood when and why.”

Anthropoids are the forerunners of present-day monkeys, apes and humans.

The newly discovered fossils fill the gap in our understanding of our evolutionary history. According to the paper describing the research, our primate ancestors in Asia were almost totally wiped out by a drastic change in the climate approximately 34 million years ago, at the juncture of the Eocene and Oligocene epochs. This event, probably caused by a large-scale rearrangement of Earth’s major tectonic plates, caused a sudden drop in temperature and humidity in many parts of the globe, forcing our ancestors to cluster around the equator and the tropics.

“Primates like it warm and wet, so they faced hard times around the world — to the extent that they went extinct in North America and Europe,” Beard said in the statement. “Of course, primates somehow survived in Africa and Southern Asia, because we’re still around to talk about it.”

Had this “global cooling” event not occurred, our evolutionary arc would have taken a different direction, as anthropoids would have continued to thrive in Asia rather than transitioning to Africa.

“This is the flip side of what people are worried about now,” Beard said. “The Eocene-Oligocene transition was the opposite of global warming — the whole world was already warm, then it cooled off.”

“The point is that primates then, just like primates today, are more sensitive to a changing climate than other mammals,” he added.