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鈥淚鈥橫 PORTRAYED as a maverick, as a cowboy scientist,鈥� says Lee Berger. 鈥淲hat鈥檚 so funny is that I鈥檓 the one following the rules.鈥�

Even if you haven鈥檛 heard of Berger, there鈥檚 a good chance you are aware of his work. He is the palaeoanthropologist behind the recent discoveries of not one but two new species of human ancestor. The finds were so remarkable that, by some accounts, they are rewriting the story of human evolution, and Berger, his team and his methods are at the centre of it.

In 2010, Berger made headlines after he (or, more accurately, his then 9-year-old son) found a trove of hominin bones belonging to what we now know as Australopithecus sediba in the hills north of Johannesburg, South Africa. It was the sort of once-in-a-lifetime find that most people in his line of work only dream of. If Berger had taken the conventional approach, he might have built the rest of his career on analysing it.

But following convention was not what Berger, an American who made South Africa his home 27 years ago, had in mind. He was convinced that even greater discoveries were waiting, particularly in the ancient caves that riddle the limestone-rich countryside.

He enlisted local help to search them, and hit the jackpot in 2013: two chambers deep inside the Rising Star cave system contained hundreds of bones from another unknown species, which his team dubbed Homo naledi. This time, the story went stratospheric, not just for the scale of the find but for its drama. One of the chambers is at the bottom of a 12-metre vertical passage just 20 centimetres across at some points and Berger recruited a team of very slim, palaeoanthropologist cavers to excavate the site. The fact that all of them were women only heightened the publicity.

Publicity is something Berger has never shied from, indeed he courts it. It鈥檚 just one of the reasons why, over the years, he has managed to upset and dismay an impressive number of his peers, including some of the most respected senior figures in the field.

The Rising Star excavations (see picture) are a case in point. Donald Johanson 鈥� one of the discoverers of the 3.2-million-year-old Lucy skeleton 鈥� has claimed the excavation should have taken months, not the 21 days Berger and his colleagues set aside. Berger responds that this was essentially a pilot excavation, although within months his team submitted several papers to Nature based on analysis of the fossils. They weren鈥檛 accepted.

In person, Berger is chatty, warm and likeable. He is clearly passionate about his subject. He is also open about his motives. In the late 1980s, Berger got his first opportunity to join a dig, in east Africa. Right from the start, he saw himself as an explorer. 鈥淚 wanted to find fossils, to make discoveries,鈥� he says, 鈥淭hat鈥檚 why I went into the field.鈥�

But opportunities in east Africa were limited. Many senior scientists had already staked claims there, he says. South Africa, on the other hand, was relatively unexplored, although hominin fossils had been found there since the 1920s. He was accepted to study for a PhD at the University of the Witwatersrand, Johannesburg, in 1990.

鈥淚 wanted to find fossils, to make discoveries. It鈥檚 why I went into the field鈥�

He never left. Berger reasoned that being able to hunt for fossils all year round would boost his chances of discovery. He says the main strategy at the time was to look for baboon fossils, since hominins were often found with them. But he wanted to look underground, not least because hominin fossils had already been found in caves. Ancient people would have made extensive use of the vast subterranean networks, he thinks. 鈥淭his dolomitic landscape is one of most stable in the world,鈥� Berger says. 鈥淚n a sense we鈥檙e standing on their land.鈥�

So far, his team has found the remains of at least 18 H. naledi skeletons, of all ages. It鈥檚 a huge hoard, particularly because many hominin species exist only as a handful of bones. 鈥淭here was a real perception that these fossils are rare,鈥� he says 鈥� and those who found them became reluctant to share access to such precious objects. 鈥淚鈥檝e watched scientists become possessive,鈥� he says. 鈥淚 vowed early on not to do that if my opportunity arose.鈥�

His critics see things differently. They argue that they work on the fossils behind closed doors not out of a sense of ownership but to make sure their published conclusions are solid. Tim White 鈥� a co-discoverer of the 4.4-million-year-old 鈥淎rdi鈥� skeleton 鈥� has insisted that good research can鈥檛 be rushed.

Yet scientists in other fields collaborate, Berger says. 鈥淚t鈥檚 what NASA or the Large Hadron Collider team does: they put as many of the best minds in the world towards a solution.鈥� Just months after the first Rising Star excavation, Berger did the same, inviting researchers 鈥� particularly young scientists 鈥� to a month-long workshop to make sense of the H. naledi material. This is what Berger means when he says he is following the rules.

This month, Berger鈥檚 team is back at Rising Star. They camp at the site even though it is just a 45-minute drive from Johannesburg: it鈥檚 about maximising time in the field, he says. A typical day begins at 5.30 am with breakfast. By 6.30 they are discussing the day鈥檚 objectives, and shortly afterwards the cavers begin to inch their way into the chambers.

This time, they are looking for evidence that H. naledi deliberately disposed of its dead, particularly signs of the fire they would have needed to navigate the deep, dark caves. It鈥檚 a controversial idea, because the most striking feature of H. naledi is that its brain was only marginally larger than a chimpanzee鈥檚 鈥� much too small, according to conventional thinking, to allow for such advanced behaviour.

Strikingly weird

But the human evolution story is changing in other ways that are making this possibility seem less remote. A. sediba existed around 2 million years ago, and we learned this year that H. naledi may have lived just 235,000 years ago, yet both have a mix of what were previously considered to be primitive and modern features. This might hint that early hominin history involved a lot of evolutionary experimentation, with an array of unusual looking species forming a family tree with many branches.

Berger says palaeoanthropologists have often assumed a simpler, linear story. This is partly because many ancient hominins are known only from fossil fragments that might fail to reveal just how strikingly weird complete skeletons can be.

This is a theme that Berger may develop. It鈥檚 an open secret that his team has made yet another ancient hominin find, unconnected to A. sediba or H. naledi. Berger is not prepared to share details yet, but he is clearly relishing the prospect.

Berger鈥檚 enthusiasm is infectious. He is a great storyteller, drawing listeners in and leaving them itching for the next chapter. It鈥檚 easy to imagine how this might get him in trouble: he does like to push the boundaries of what can be learned from the evidence to hand.

But there is so much more evidence waiting to be found, he says. 鈥淭hese hominin fossils are just not as rare as we once thought. We were looking in the wrong places.鈥� When I ask about the scientific legacy he might leave, Berger鈥檚 answer picks up on this idea. 鈥淚n 50 years, this might be looked on as the moment when we grew into an evidence-based science,鈥� he says. 鈥淚 hope that this snowball we鈥檝e pushed off the hill is going to lead to more and more fossils.鈥�

In other words, he says, he would like his research to inspire so many others to make spectacular discoveries that A. sediba and H. naledi no longer stand out as exceptional. 鈥淭hat would be my dream.鈥�

This article appeared in print under the headline 鈥淭he ultimate origin story鈥�