You've probably heard that our family tree got a new member on Thursday. Homo naledi, a primitive, small-brained member of our genus, made itself known in a big way when cavers stumbled upon a mass grave left by the species.

But the discovery of the new species, a cousin of our own, wouldn't have been possible without six female scientists who are being called "underground astronauts".

Video shows female scientists and experienced cavers recovering fossil remnants of new species of human relative in November 2013 at the Cradle of Humankind Heritage Site in South Africa. The women were chosen via social media because they were slender enough to move through the cave's narrow passageways to get to the fossil chamber, 100 yards from the cave entrance. (NOVA/National Geographic)

Here's the story: When lead researcher Lee Berger first got word of the possible fossil find from some cavers, he was left in a quandary. The cavers (Rick Hunter and Steven Tucker) who had squeezed into the breathtakingly tight cave segment didn't have the skills to safely collect and transport the strange skeletal remains they'd seen.

[Full story: Fossils found in African cave are new species of human kin, say scientists]

And with such a tight squeeze (really tight -- see National Geographic's illustration if you dare), Berger knew he lacked the physique and caving skills needed to get inside himself.

So he put out a call for skinny, highly-qualified paleontologists or archaeologists who could shimmy in and out of caves with the best of them. Of 60 applicants, he picked the most qualified six -- and they were all women.

“Looking down into it, I wasn’t sure I’d be OK,” Marina Elliott, one of the six female scientists Berger called his "underground astronauts", told National Geographic. “It was like looking into a shark’s mouth. There were fingers and tongues and teeth of rock.”

In a video for News24, Elliot explained that the first trip down, while scary, was mostly exciting. As a seasoned caver, she was excited to explore a new chamber.

[Women welcome in ‘hard working’ fields, but ‘genius’ fields are male-dominated, study finds]

"Everywhere that I shone my headlamp, I could see fragments of bone," she said. "So it was very obvious at that point that we were dealing with a lot of material. But even then we didn't realize that it was going to all be hominin, and be as momentous as it has been."

In fact, the bones were so numerous that Elliot and the other female cavers took to removing their boots in another portion of the cave -- going barefoot on the actual excavation site --  to make sure they didn't crush any fragments.

Elliot, who's now doing postdoctoral research at the University of the Witwatersrand, was the first one down into the chamber. She was joined by Becca Peixotto, a PhD student at American University; K. Lindsay Hunter, a biological anthropologist who's since moved on to more field research; Elen Feuerriegel, a PhD candidate at the Australian National University; Hannah Morris, a new PhD student at the University of Georgia; and Alia Gurtov, a University of Wisconsin – Madison PhD candidate.

The women worked in groups of three, trading off two-hour shifts in the fossil chamber. From National Geographic:

Over the next several days, while the women probed a square-yard patch around the skull, the other scientists huddled around the video feed in the command center above in a state of near-constant excitement. Berger, dressed in field khakis and a Rising Star Expedition cap, would occasionally repair to the science tent to puzzle over the accumulating bones—until a collective howl of astonishment from the command center brought him rushing back to witness another discovery. It was a glorious time.

After over three weeks of digging, their haul clocked in at over 1,500 bones -- the largest discovery of its kind ever made in Africa. And after analysis, of course, it yielded an exciting new species to boot.

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