In fact, fossils found over the past several decades have increasingly complicated our understanding of human evolution. Our early ancestors did not simply become bigger brained and more upright over time. They also begat other lineages—Homo naledi is an example; Homo neanderthalensis in Europe is another—of which modern humans are the only extant branch. The dating of Homo naledi to a minimum of 236,000 years old provokes more questions, and Berger is no stranger to provocations.

All of this is addressed in three new papers from Berger and his collaborators—totaling over 100 pages—published today in the journal eLife. The first paper provides the age of the original fossils. The second announces the discovery of a second chamber in the same South African cave system, containing over 130 Homo naledi fossils including a nearly complete skull. The third and most speculative paper takes up the question of how Homo naledi evolved and revisits a controversial hypothesis for the presence of these fossils in the cave.

The dating paper has solid evidence—at least as solid as you can get with ancient bones. “They have thrown basically every available dating method in the book at the remains,” says Justin Adams, a paleontologist at Monash University who has also worked in South African caves. The study uses a total of six methods, including measuring the levels of uranium and thorium in layers of stone that have formed over the fossils. This gave a minimum age of 236,000 years. An even more informative method looked at the fossils themselves, specifically three teeth. Radiation from radioactive elements like uranium and cosmic rays are fairly predictable over time and they leave a signature when they bombard tooth enamel; the more evidence of this radiation, the older the tooth. This method is called electron spin resonance dating.

“It’s taken a long time to do this properly,” says Paul Dirks, a geologist at James Cook University who led the dating work. Other paleontologists had criticized the team for rushing to announce Homo naledi in 2015 before the dating work was complete. Even though the team didn’t give a possible age for the fossils, the discovery announcement fueled speculation that the fossils were more than a million years old based on the ancient-looking morphology. “Not publishing a date actually exposed the frailty of many of these morphological interpretations,” Dirks says. It’s happened before in the history of paleoanthropology. Susan Antón, a anthropologist at NYU who was not involved in this work, notes that researchers had previously misdated hominin fossils found on the island of Java in Indonesia when they looked at morphology alone.

The team is now working on dating fossils in Lesedi, the second chamber, which look morphologically identical to the Homo naledi in the first chamber. Lesedi was a little easier to access. Berger, who couldn’t fit in the first chamber, did get to see the inside of Lesedi—once. “I got stuck coming out and decided I’m never coming in again,” says Berger. His team named that section of the chamber the Berger Box.

This second chamber of Homo naledi bones further complicates Berger’s most controversial hypothesis—that the bodies were intentionally buried in the cave, which suggests some kind of complex culture. They based this hypothesis in part on the difficulty of accessing the first chamber and the lack of animal marks or bones to suggest animals moving the bones. Well, this second chamber is slightly easier to access, and it contains plenty of animal bones. This neither proves the the hypothesis or conclusively disproves it—but that’s the challenge of working with scant evidence in paleoanthropology.