Puzzling Human Relative Homo Naledi May Have Lived at the Same Time as Our Ancestors

Two views of an adult Homo naledi cranium found in the Lesedi Chamber of the Rising Star cave system in South Africa, where the remains of 15 individuals were discovered in a different cave in 2013.
Two views of an adult Homo naledi cranium found in the Lesedi Chamber of the Rising Star cave system in South Africa, where the remains of 15 individuals were discovered in a different cave in 2013.
Hawks et al. in eLife, 2017

It's tempting to think that evolution works in a straight line, with clearly defined, graduated steps from primitive to modern. We humans are especially prone to telling our own evolutionary story in this manner. Evolution doesn't work that way, though, and we aren’t even the end point of human evolution, but works in progress. (Personally, I hope we are amphibious and have fins in 3 million years. That would be awesome.)

The latest evidence for that essential truth comes from the Rising Star cave system in South Africa, where scientists say Homo naledi, the unusual hominid species they discovered there in 2013, is surprisingly young, living as recently as 236,000 years ago. That means it was one of various hominids wandering the Earth at the same time as the Neanderthals in Europe; the Denisovans in western Asia; the ancestors of the “hobbit,” Homo floresiensis; and, in Africa, potentially alongside the earliest members of our own species, Homo sapiens.

Moreover, the researchers found three more individuals in another chamber in the cave system, one of them with the most complete H. naledi skull discovered yet. (You can see it above.) Today the large team of researchers published a trio of papers documenting their results in the open-access journal eLife.

In 2015, we reported on the initial discovery of 15 sets of hominid remains found in the Dinaledi cave by a team of researchers led by paleoanthropologist Lee Berger. It was an unprecedented bounty of bones. Often, paleoanthropologists are reconstructing human evolutionary history from scant remains—a fragment of skull or jaw bone here, a femur or a finger there. But in the Dinaledi cave, there are at least 1500 bones, and likely a lot more, since only a small fraction of the cave was excavated by a half-dozen archaeologists—all female, all cavers, all slim enough to squeeze through a series of cave tunnels that narrowed to just 7 inches in one spot—who worked in extraordinary conditions to excavate the bones from a pitch-black cave nearly 100 feet beneath the surface.

The ancient creatures were no bigger than the small but formidable women who unearthed them. Slender and about 5 feet tall as adults, they would’ve weighed just under 100 pounds. Their bodies are a fascinating mosaic of primitive and modern: tiny, orange-sized brains housed in skulls with jaws and teeth closer to early Homo; shoulders suited for climbing trees but feet and ankles made for walking; hands potentially capable of making tools, but with fingers well-curved for tightly gripping tree branches.

The discovery made headlines worldwide. Most of us—whether scientist or science nerd—fascinated by the find had one question: How old were they?

DATING THE REMAINS

When H. naledi was first discovered, the researchers deliberately didn’t attempt to answer that question. Determining where a species fits into the evolutionary record based on its morphology is not an unusual approach, but it can also be misleading. In the past 1.5 years, other scientists have proposed ages for H. naledi that range from 100,000 to 2 million years ago.

In one of the current studies, researchers led by James Cook University geologist Paul Dirks conducted six dating tests to narrow the age range, including the paleomagnetic dating of calcite left behind by running water and a chemical analysis of three fossil teeth discovered in the cave using a technique called combined U-series and electron spin resonance (US-ESR) dating. From all the tests, they came up with an age range: they're most likely between 236,000 and 335,000 years old.

As eLife notes in a commentary on the study, “The estimated dates are much more recent than many had predicted, and mean that H. naledi was alive at the same time as the earliest members of our own species—which most likely evolved between 300,000 and 200,000 years ago. These new findings demonstrate why it can be unwise to try to predict the age of a fossil based only on its appearance, and emphasize the importance of dating specimens via independent tests.”

American Museum of Natural History paleoanthropologist Ian Tattersall echoed that sentiment to Mental Floss. “This is an object lesson in trying to date anything by what it looks like,” he says. While he doesn't find the age estimate surprising, he’s less convinced that H. naledi belongs in our Homo genus: “Anything as odd as this is always going to be tough to fit into both a phylogeny and a timescale,” he notes.

Did our ancestors interact with this oddball? We have no idea. But we do know that the picture of human evolution continues to expand in detail and complexity with every discovery like H. naledi.

Bioarchaeologist (and regular Mental Floss contributor) Kristina Killgrove, who teaches biological anthropology, human origins, and evolutionary theory at the University of West Florida, tells us that the long wait for H. naledi dates was “worth it.”

She says, “These dates reveal a much more complicated story of hominin evolution than ever before. We used to think of human evolution as a single lineage—the classic image of the progression from apes to humans. But H. naledi shows that palaeoanthropologists are onto something far more complex—and far more interesting! While these new dates won't make it into textbooks in time for the fall semester, I will certainly be updating my human evolution lectures this summer."

ONE NEW CAVE, THREE NEW BODIES

Whatever we have to learn about this cousin of humanity can only be helped by the other discovery reported today in eLife: 133 bones from three likely H. naledi individuals—two adults and one child—found in another cave in the Rising Star system. First spotted in 2013 by cavers, the bones were unearthed in three locations in a cave the researchers coined Lesedi. The two caves are found at the same depth, but they’re not directly connected.

As with the first expedition into the Dinaledi cave, the working conditions for the researchers weren’t easy: Wits University archaeologist Marina Elliott, who led the intrepid team of “underground astronauts” who excavated both sites, told National Geographic that while the Lesedi cave was slightly easier to reach than Dinaledi, she still had to excavate one set of remains from a 2-foot-wide alcove while laying on her chest, her shoulders pinned between rocks. “It’s extremely physically difficult,” she said. “I’ve tried to do a lot of yoga to get myself to be able to do it.”

Elliott would probably say it was worth it, though; the remains she excavated in that location yielded the most complete H. naledi skull so far discovered. Dubbed Neo (after the Setswana word for "a gift," not the The Matrix character), this adult has a larger skull—and therefore a larger brain capacity—than the other specimens so far discovered, but it falls within an expected range.

ARE THESE BURIALS OF A SORT?

One of the most contentious theories Berger and the team proposed when the first H. naledi fossils were discovered was that these bodies had been intentionally placed in the cave in some sort of death ritual. Berger and John Hawks, a paleoanthropologist at the University of Wisconsin, revisit that theory in the third paper published in eLife. They point out that the caves are difficult to access and aren’t obvious “death traps” that individuals could’ve accidentally fallen into. Nor did the remains show any signs of mass death, having been fed upon by carnivores or scavengers, or of having been flushed into the caves by a water system.

So how did they get there?

The researchers write, “We propose that funerary caching by H. naledi is a reasonable explanation for the presence of remains in the Dinaledi and Lesedi Chambers. Mortuary behaviors, while culturally diverse, are universal among modern human cultural groups. Such behaviors are not seen in living non-human primates or in other social mammals, but many social mammals exhibit signs of grief, distress, or other emotional response when other individuals within their social group die.”

They say that while there’s no evidence of symbolic thinking among H. naledi, such sophisticated thought isn’t necessarily a requirement for a death ritual. The “physical and social effects of the deaths of group members” could have been motivation enough.

“Such behavior may have many different motivations, from the removal of decaying bodies from habitation areas, to the prevention of scavenger activity, to social bonding, which are not mutually exclusive,” they note. “We suggest only that such cultural behavior may have been within the capabilities of a species that otherwise presents every appearance of technical and subsistence strategies that were common across the genus Homo.”

Homo Erectus Might Have Been Really Lazy

Shipton et. al,
Shipton et. al, PLOS ONE (2018)

Of all the human species that once roamed the world, only one remains—us. Why did our primitive cousins go extinct? For Homo erectus, something like laziness may have played a role, Cosmos reports.

A new study in the journal PLOS ONE explores the role that H. erectus's lack of drive may have contributed to its extinction. The international team of researchers based their analysis on an excavation of a paleolithic site in central Saudi Arabia, finding that the tools H. erectus made were of consistently lower quality than what tool makers in later periods used. Their tools were constructed with whatever material was easiest to get, rather than what would make the best tools.

And it wasn’t because better materials weren’t available. "At the site we looked at, there was a big rocky outcrop of quality stone just a short distance away up a small hill,” study co-author Ceri Shipton of the Australian National University said in a press release. “But rather than walk up the hill, they would just use whatever bits had rolled down and were lying at the bottom.” He added, “They knew it was there, but because they had enough adequate resources, they seem to have thought, ‘why bother?’”

A row of stone tools excavated from Saffaqah
Some of the stone tools
Shipton et. al, PLOS ONE, (2018)

Meanwhile, other hominin species, like our own Homo sapiens, were happily clambering up mountains to seek out better materials for their tools. Shipton suggests that H. erectus lacked the tendency toward exploration and curiosity that has helped our species thrive.

This “laziness,” combined with changes to their environment, was likely what did in H. erectus. As the humid environment around them became drier, H. erectus seemingly didn’t adapt: They didn't invent new kinds of tools to deal with the changing landscape, nor did they relocate or travel farther afield. The research team found the tools largely near dry river beds, suggesting that H. erectus neither progressed technologically nor modified their behavior for their altered habitat.

H. erectus did manage to walk upright as we do—a first in human evolution—and it was likely the first hominin to expand their habitat beyond Africa. But the combination of these two newly identified shortcomings may have contributed to H. erectus's demise.

[h/t Cosmos]

Intriguing New Theory Might Explain the Fate of Easter Island's Civilization

iStock
iStock

Standing up to 33 feet high and weighing 81 tons, the huge moai statues of Easter Island (Rapa Nui) are the most recognizable artifacts of a thriving civilization that peaked at the middle of the last millennium. For hundreds of years, Polynesian peoples lived on the small island 2300 miles west of Chile and developed a complex culture. By the 1700s, when Europeans first arrived, much of the society was decimated.

For years, scientists thought they knew why—but fresh archaeological evidence has provided an alternative theory.

The Journal of Pacific Archaeology published a paper [PDF] this week contradicting the commonly held belief that, in the 1600s, Rapa Nui's inhabitants descended into a Lord of the Flies–like era of infighting and violence as a result of dwindling resources. According to new research, the island’s population may not have devolved into barbarism. Instead, they were collaborating on toolmaking.

University of Queensland archaeologist Dale Simpson, Jr. theorized that the raw materials used in the carving tools would reveal clues about the dynamics of the community. He and his colleagues collected 17 tools found near the moai, including axe-like toki. Using a mass spectrometer to analyze the chemical composition of the tools and samples from stone quarries on the island, Simpson and his colleagues found that most of the toki came from a single quarry.

Simpson believes this is evidence that Rapa Nui's people had not fallen into violent conflict, but were instead sharing resources—or at least allowing one another access to a favorite quarry for tool production. If the islanders were split into factions, it’s unlikely that whoever was controlling the quarry would permit rivals to make use of it.

If accurate, it would join other recent theories that are drawing a revised picture of Rapa Nui's civilization. Explorers once described a surplus of spear-like objects presumably used for combat, but modern researchers examining the tools (called mata’a) in 2015 found that their surfaces were too blunt to pierce skin and were probably used for tilling soil.

While Simpson's take on the newly discovered carving tools is an intriguing theory, researchers aren't ready to rewrite history just yet. Other scholars, including study co-author Jo Anne Van Tilburg, point out that raw materials for the tools could have been seized by force or some form of coercion.

More research will be needed to see if Simpson’s new theory holds up. If it does, it would present a new wrinkle in the storied history of Rapa Nui.

[h/t Gizmodo]

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