Meet your long-lost distant cousin, Homo luzonensis

Overall, “ shows a pattern that is not seen elsewhere in the genus ,” wrote Détroit and his colleagues in a paper published today in . In other words, its teeth look different from any other species, so it’s probably a species we’ve never seen before.

But on the other hand…

The few hand and foot bones we have from look a lot more like Australopithecines.

One of the finger bones (the middle bone of one of the fingers on the left hand) and a toe bone (the base of one of the middle toes on the right foot) are both curved, which is something you’d expect to see in older members of our family tree, like . And the way the end of the toe bone would have lined up with the metatarsal (a bone in the mid-foot) also looked more like an Australopithecine than like or a modern human.

“You could drop that bone among the fossils from 3 million years ago in Ethiopia in Hadar, and you wouldn’t be able to pull it out,” anthropologist Matthew Tocheri of Lakehead University, who wrote a paper commenting on the discovery, told Ars Technica. “I don’t think there’s anyone in this field who would say that that looks like what you might expect the toe bones of to look like. Instead, it’s the exact opposite; you expect the toe bone of to look a lot more like our toe bones, where they’re significantly shorter and the morphology has changed quite dramatically from what we see in earlier hominins.”

Curved phalanges are usually the mark of a life spent doing a lot of climbing. Bones rebuild and remodel themselves constantly throughout our lives, so their final shape reflects the kinds of stresses we put them under. If you were an early hominin, you’d be climbing and hanging around in trees about as often as you walked on the ground. After spending a lot of time gripping branches with your weight hanging below your arms, the bones at the base of your fingers would curve slightly to help bear the strain better. Curved toe bones suggest gripping with the feet.

That reveals more about an individual’s lifestyle than their genetics, but it may suggest that navigated the world with a mix of walking and climbing, similar to Lucy and other Australopithecines who first emerged 3 million years ago.

Of course, two fingers and two toes aren’t much to go on, and Détroit and his colleagues caution that we don’t yet have enough information about to draw firm conclusions about how the species moved around. But they do say that the bones look distinctly more Australopithecine than , and that may mean that the human story is more complex than we thought.

Intrigue in the family tree

lived and died just 2,800km (1,730mi) from the Indonesian island of Flores, where archaeologists discovered the fossil remains of a diminutive hominin species called . Nicknamed the Hobbit, it dates from 100,000 to 60,000 years ago. That discovery dropped a very strong hint that the story of and its descendants among the islands of Southeast Asia might have been more complicated than we thought—and was so a long time before Denisovans and modern humans showed up.

“These new fossils, and the assignation of them to a new species (), fulfills one of the predictions Mike Morwood and others (myself included) made when we first reported (15 years ago!) the discovery : that other unknown species of hominins would be found in the islands of Southeast Asia,” anthropologist Richard Roberts told Ars. (He’s a co-discoverer of and based at the University of Wollongong.) “So, while in some ways a new species in the region is not unexpected, it is nonetheless exciting to see this new material finally come to light.”

And it raises the intriguing (but totally speculative, so far) prospect that others may still be waiting to be found.

Both Luzon and Flores have been separated from the nearest mainland since well before hominins ventured into the region, so whatever groups of hominins made it to the islands (possibly washed ashore by accident) would have been isolated for hundreds of thousands of years afterward. As a result, they were free to evolve in their own directions. The result may have been a sudden branching of the hominin family tree into several new species. Today, they provide an opportunity for anthropologists to watch the same story play out, in parallel, on different tropical islands.

and have enough in common to suggest a common ancestor. “The skeletons of both species present anatomical traits that are either rare or absent elsewhere in the genus but have similarities with those of Australopithecus,” wrote Détroit and his colleagues. It’s likely that the two species share a common ancestor that they don’t have in common with us, similar to the way we’re more closely related to Neanderthals and Denisovans than to Right now, however, there’s not enough evidence yet to be sure, and no DNA from either species so far.

A family mystery

The most widely accepted version of this idea is that that common ancestor is . There is fossil evidence of the species’ presence in Asia during the right time period to have given rise to , and there’s no fossil evidence of any other hominin species in the area at the same time. When authors did a statistical analysis of every feature they could quantify, looked more like Asian specimens than like any other known species. They suggest that ’ dwarfism evolved on Flores (and we know the same thing happened with modern humans on the island), and that ’ Australopithecine-like feet and hands evolved on Luzon in a way that just coincidentally happened to resemble its earlier relative.

But Tocheri, whose work focuses on hands and feet, says that’s possible, but he argues that it’s less likely than the idea that other very early members of may have left Africa at around the same time as In this view, and look a bit like those earlier hominins because that is, in fact, who they’re descended from. Several species like and , which evolved earlier and had more Australopithecine-like traits, were still around when was beginning its Eurasian expansion, and Tocheri says that 2.1 million-year-old stone tools found in China last year may suggest an even earlier hominin migration.

“If we have missed these species that lived less than 100,000 years ago, how much are we missing from the earlier phases of evolution?” anthropologist John Hawks of the University of Wisconsin, co-discoverer of , told Ars in an email commenting on the study. “Could there have been earlier dispersals that we haven’t noticed because of bad search strategies and bad assumptions? I wouldn’t bet against finding that hominins were out of Africa a lot earlier than we thought.”

At the moment, we don’t have direct fossil evidence one way or the other, and what we have comes from late in ’ and ’ time. Stone tools and butchered animal remains on both islands suggest that hominins were there as early as 700,000 years ago. Learning whether those early occupants looked more like Lucy or more like could help sort out the family mystery.

, 2019. DOI: 10.1038/s41586-019-1067-9;(About DOIs).

Kiona N. Smith Kiona is a freelance science journalist at Ars Technica.
Twitter@KionaSmith07

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