Surprising New Information About Homo naledi

The Atlantic (and other outlets) has a story on new information on the date of the Homo naledi fossils from Rising Star Cave and it is...surprising.  As Sarah Zhang writes:

The one thing everyone agrees is that the fossils themselves are spectacular. In 2015, researchers unveiled 1,500 hominin fossils found deep in a South African cave, excavated by six cavers who were all skinny, short, and female. The hominin, a new species the team christened Homo naledi, was an unusual mix of the old and modern. Their heads were small, suggesting an early hominin perhaps more than a million years old. But their feet were stiff for walking upright and their hands adept like modern humans.

So in the media frenzy that followed—a National Geographic cover, a documentary, numerous articles—the question kept coming up: How old are these Homo naledi fossils, really? What do they tell us, if anything, about the origin of Homo sapiens?

To that first question, the researchers now have an answer: 236,000 to 335,000 years old. As for the second question, well, it’s complicated. “You can’t tell simple stories anymore,” says Lee Berger, a paleoanthropologist at the University of the Witwatersrand who led the research. “This is the gigantic message out of Homo naledi.” The age of these fossils puts these strange, small-brained yet human-like hominins in South Africa just before the emergence of the first anatomically modern Homo sapiens.

Holy Liang Bua, Batman!  If the bones really are 236k, then that would put them roughly 40-50 k years before the advent of modernity represented by the Omo 1 cranium.  Admittedly, that skull is fragments “swimming in plaster” but we have a pretty good idea of what it looks like. We certainly have modernity in the Bouri remains from Herto at 160 ky.

How do we know how old the fossil are?  From the eLife article:

Now, Dirks et al. – who include many of the researchers who were involved in the discovery of H. naledi – report that the fossils are most likely between 236,000 and 335,000 years old. These dates are based on measuring the concentration of radioactive elements, and the damage caused by these elements (which accumulates over time), in three fossilized teeth, plus surrounding rock and sediments from the cave chamber. Importantly, the most crucial tests were carried out at independent laboratories around the world, and the scientists conducted the tests without knowing the results of the other laboratories. Dirks et al. took these extra steps to make sure that the results obtained were reproducible and unbiased.

More specifically, they did Electron Spin Resonance (or Electron Paramagnetic Resonance), Uranium-Thorium disequilibrium, Optically Stimulated Resonance and radiocarbon dating.  This is probably not the last word on the dating of the fossils and there are quite a few assumptions that have been made regarding the provenance of the fossils to the cave sediments, but this is the closest thing that we currently have. One of the critical problems in dating much of the South African cave deposits is their relationship to the hominins found there.  Often, the caves opened up at the top and the fossil remains either fell in, were dropped in or they crawled in.  What makes the Rising Star remains so peculiar is that this cave did not form in the traditional way and the bones were so far into the cave. 

Where does this leave us? It leaves us with more questions than answers.  It has been common consensus that, while there was considerable variability in hominin morphology throughout the Pliocene and early to middle Pleistocene, that this "settled down" and that variability diminished as we made the transition to modern humans.  These fossils suggest the opposite: that large amounts of variability were, in fact, present throughout the range of human existence and only recently (200ky to the present) did this variability drop off.

I am quite sure that more studies will be done to elucidate the relationship that these fossils (there are more very similar fossils next door in the Lesedi cave complex) have to other forms in Africa.  There are obviously very peculiar cultural interactions going on, though (or lack, thereof).  With the Liang Bua remains in East Asia, hypotheses of endemic dwarfism and isolation have been put forth to explain why these remains are so diminutive and primitive.  It is more difficult to put forth these same arguments here where there are few to no barriers to migration and interaction between groups. 

H. floresiensis Not As Young or As Unique As We Thought

In other words, so much for the pathology argument.  Many news outlets, National Geographic being one of them, are reporting on new fossils that closely match those of Homo floresiensis that were found at Liang Bua Cave on the island of Flores in the late 1990s.  Adam Hoffman writes:

The 700,000-year-old human remains are the first found outside Liang Bua cave, the site on Flores that yielded the original hobbit fossils. The much older samples show intriguing similarities to H. floresiensis, including their small size, and so provide the best evidence yet of a potential hobbit ancestor.

“Since the hobbit was found, there have been two major hypotheses concerning its ancestry,” says Gerritt van den Bergh, an archaeologist at the University of Wollongong in Australia and a contributor to the work.

According to one theory, H. floresiensis is a dwarfed form of Homo erectus, an ancient human relative that lived in East Asia and parts of Africa until about 143,000 years ago. But other researchers think the hobbits evolved from even earlier, smaller-bodied hominins such as Homo habilis or Australopithecus.

“These new findings suggest that Homo floresiensis is indeed a dwarfed form of Homo erectus from Java, a small group of which must have gotten marooned on Flores and evolved in isolation,” van den Bergh says.

The article goes on to note that the competing argument, that the fossils of Liang Bua represent some kind of pathological condition, and that they maintained this condition for some 700 ky, is now untenable. Clearly this is a side-branch of human evolution.The other key finding is that they also had stone tools, specifically a “straightforward core and flake” technology. Further, the tools show a striking similarity to those found at Liang Bua, suggesting that there was remarkable cognitive "stability" in this population. 

The more we think we know about human evolution, the less, it turns out, that we do.  For now, the entire article is available from Nature for free here. 

Homo floresiensis Gains Legitimacy

Science Daily has posted a story detailing new examination of the Liang Bua crania by researchers at SUNY Stonybrook, The University of Tubingen, and the University of Minnesota in which they grant legitimate species status to Homo floresiensis.  They write:

The scientists applied the powerful methods of 3-D geometric morphometrics to compare the shape of the LB1 cranium (the skull minus the lower jaw) to many fossil humans, as well as a large sample of modern human crania suffering from microcephaly and other pathological conditions. Geometric morphometrics methods use 3D coordinates of cranial surface anatomical landmarks, computer imaging, and statistics to achieve a detailed analysis of shape.

This was the most comprehensive study to date to simultaneously evaluate the two competing hypotheses about the status of Homo floresiensis.

The study found that the LB1 cranium shows greater affinities to the fossil human sample than it does to pathological modern humans. Although some superficial similarities were found between fossil, LB1, and pathological modern human crania, additional features linked LB1exclusively with fossil Homo. The team could therefore refute the hypothesis of pathology.

The link to the PLoS paper is here.This is the conclusion of the paper:

Our analyses corroborate the previously suggested link between LB1 and fossil Homo and support the attribution of this specimen to a distinct taxon, H. floresiensis. Furthermore, the neurocranial shape of H. floresiensis closely resembles that of H. erectus s.l. and particularly specimens of early Eurasian H. erectus, although it is unclear whether this latter affinity is best attributed to a close phylogenetic relationship or to a size-related convergence in shape. These results also counter the hypotheses of pathological conditions as the underlying cause of the LB1 neurocranial phenotype, with the possible exception of posterior deformational plagiocephaly, a condition without significant adverse health effects.

Of course, this doesn't mean that it is not endemic dwarfism, just that it is not built on a modern human base. In this case, it may represent a Homo erectus base. Why it was so marked is still an unanswered question.It is also quite possible that this represents founder effect followed by years of selection for diminutive characteristics.  It definitely represents a peculiar side branch in human evolutionary history but not one that defies explanation. 

Small People, Big Bird

The BBC is reporting on a fossil discovery on the island of Flores, the last known home of Homo floresiensis. The size of the bird: 1.8 meters tall. Emma Brennand writes:

The bones, thought to be belong to a single stork, are between 20,000 to 50,000 years old, having been found in sediments dating to that age.

The giant bird is the latest extreme-sized species to be discovered once living on the island, which was home to dwarf elephants, giant rats and out-sized lizards, as well as humans of small stature.

"I noticed the giant stork bones for the first time in Jakarta, as they stood out from the rest of the smaller bird bones. Finding large birds of prey is common on islands, but I wasn't expecting to find a giant marabou stork," Dr Meijer told the BBC.

She also writes that it might have been able to prey on the hominins, but there is no evidence that it did. What the heck is in the water out there?

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New Research Pushes Back Occupation of Flores

It is now thought that the inhabitants of the island of Flores, from whence come the hominid euphemistically known as "the hobbit," may have been on the island as early as one million years ago. NewsDaily picks up the Reuters story:

In their paper, the researchers said they found 45 stone tools in Wolo Sege in the Soa basin in Flores.

Led by Adam Brumm at the Center of Archaeological Science in the University of Wollongong in New South Wales, Australia, the researchers used new dating methods and found that the stone tools were about a million years old.

"It is now clear, however, in light of the evidence from Wolo Sege, that hominins were present on Flores (a million years ago). This suggests that the non-selective, mass death of Stegondon sondaari and giant tortoise ... could represent a localized or regional extinction," they wrote in their paper.

A lot of evolution can happen in a million years.

Pictures of the Liang Bua Excavations

The Sacramento Bee has lots of high resolution pictures of the excavations taking place at Liang Bua, the site of the discovery of Homo floresiensis.

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