TwilightBeasts

“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies, were made in the interiors of collapsing stars. We are made of star stuff.” (Carl Sagan, Cosmos)

New hominin species are a rare and unique find. Just weeks after paleoanthropologists were discussing some pruning to what has become the progressively gnarled bush representing the Homo lineage, a newly announced discovery has added yet another branch. The remains of at least 15 individuals belonging to a new species, Homo naledi, have been recovered from deep within the Rising Star cave system just outside of Johannesburg, South Africa. The species name “naledi” refers to the finds within the Rising Star Cave, and means “star” in Sesotho, one of South Africa’s 11 official languages.

Naledi: A beautiful name for one of paleoanthropology’s rising stars. (Image by K Lindsay Hunter)

The site itself lies within a well-traveled and much explored area. Rising Star is actually a popular destination for the local caving club (Speleological Exploration Club, SEC), and if you have gone on such a trip in the last 50 years, there is a good chance that you have been there. The cave system is less than a mile from two other very important hominin-bearing sites: Swartkrans and Sterkfontein. The first fossil finds of early hominins in South Africa, Australopithicus africanus, were discovered at Swartkrans, while more examples of Au. africanus, and possible fossils belonging to Homo, were found at the rich site of Sterkfontein. With sites such as these, and these newly discovered fossils, you can see why the area is called the Cradle of Humankind.

Serendipity played its part in the discovery, as it always does, but so did fortuitous outreach from the local university. In late 2013, Professor Lee Berger of the University of Witwatersrand had recently realized that he had neglected exploration in the wake of his successful discovery of the Au. sediba site of Malapa. To remedy this, he asked his colleague Pedro Boshoff, a caver, to let his friends know to keep their eyes open for possible hominin fossils as they went about their more routine cave exploring.

The actual discovery was made by two recreational cavers and SEC members, Rick Hunter and Steven Tucker, on a very lucky Friday the 13^th, 2013 while pushing the cave for a possible extension. The part of the cave that Rick and Steven meant to ‘push’ was a spectacular disappointment, leading to an area only about the size of table. As they still had much of the night ahead of them, Rick asked Steven to do some climbing in an area of the cave known as “the Dragon’s Back.” This colorful name refers to a large formation that had fallen from the ceiling sometime in the distant past, providing a challenging climb as though along the beast’s back toward its outstretched head. Once tackled, Rick decided to film some formations using his GoPro, and found Steven was in his way. To dodge the camera, Steven fitted himself into a tiny slot in the floor of a small antechamber.

The Steven and Rick Show: Steven Tucker hands Rick Hunter a bag of peanuts after first dingling him in the face with them during the expedition. (Image by K Lindsay Hunter)

Because he’s a caver, and such people have notoriously high energy levels and short attention spans when faced with unknown spaces, Steven decided to wriggle down feet first and see if his resting space went anywhere. A few moments later, he found his feet dangling 4 meters in space above another chamber completely obscured from the top. He quickly yelled up to Rick the words that every caver loves to hear: “It goes,” which is to say, the cave extends, and there is more to explore. Not needing to be told twice, Rick quickly squirmed down the 12 m chute (20–25 cm on average, with an ~18 cm pinch point), and joined Steven at the bottom. As they made their way around the small antechamber and into what is now known as “the Dinaledi Chamber” (“the Chamber of Stars”), they saw what looked like human bones littered along the floor. One in particular caught their attention, a mandibular fragment (lower jaw) with teeth attached. The thought went through their minds that this was the last caver to have entered the area, but not having made it back out, this would seem to explain why the chamber wasn’t found on any survey map (this despite the fact that a survey marker could be seen on the wall of the chamber). They put this thought from their minds and carried on looking for any possible extensions to their new playground. Finding none, they resolved themselves to looking about at their long dead companions. The idea began to dawn on them that perhaps they had stumbled upon fossils like those they had been asked to alert Pedro to, but having neither specialist knowledge, nor camera batteries by this point, further progress on the subject was left until the following week.

The Dinaledi chamber, showing the distribrution of the fossils on the cave floor. (Image from Dirks, et al 2015. From here)

September 19, the two returned and took photos for a very excited Pedro (who viewed them on October 1—honestly, cavemen are useless with comms!), who then quickly delivered them in person to an astonished Lee. Following another round of photos (this time with a metric scale and taken by Lee’s teenage son, Matthew (discoverer of Australopithecus sediba), Berger knew it was time to act.

Now, the process of funding and mounting a paleoanthropological expedition is usually a long and tedious exercise in bureaucracy and money-wrangling. Very fortunately, in the case of Rising Star, Lee was able to prevail upon his position as a National Geographic Explorer-in-Residence and parlayed the confidence the foundation had in him, his skill, and his judgment into a 21-day expedition to kick off at the beginning of November 2013.

To crew this expedition, Lee turned to social media. He knew from conversations with those who had been within the Dinaledi Chamber that he was too large to pass through the entrance chute. With some regret, he knew that he would have to trust the expertise of experienced paleoanthropologists/paleontologists/archaeologists whose body frames, skills, and athleticism would permit them to pass into an area that he could not. In the recent PBS Documentary, Dawn of Humanity, Lee says he expected maybe a handful of responses to a post he made on Facebook. He received almost 60 qualified and eager applicants. Of this number, 6 were ultimately selected, all women, who fit this demanding criteria. We arrived in South Africa on or near the 5^th of November, not even two months since the discovery.

Rising Star Expedition Facebook ad posted on social media by Lee Berger around October 7 2013. (Credit: Facebook, Lee R. Berger)

I say “we,” because I was fortunate to be selected as a member of these so-called “Underground Astronauts” (or Advance Underground Scientists or Advance Speleological Archaeologists, as we were known on site). I am also now married to one of the original co-discoverers, Rick Hunter, so I am in, perhaps, an unique, if not entirely unbiased, position to shed light on the goings on within, as well as the occupants of this Chamber of Paleo-Secrets (no longer).

The Rising Star Expedition in 2013 formed a small, but lively and tight-knit community of scientists, local cavers (mostly SEC members), Nat Geo crew, and support staff. Ensconced with a roommate in military tents, we were baked awake around 5:30 AM, to stumble to the mess tent for our caffeinated beverage of choice. Following the morning briefing, we divided into shifts of two or three advance underground scientists to begin what could be as long as 8 hours of excavation. This was all performed under the watchful eye of both cavers within the system and scientists top-side in the Command Tent.

The original team of 6 underground astronauts. This is the Rising Star team who crawled in the cave and excavated the incredible fossils. From left to right: Becca Peixotto, Alia Gurtov, Elen Feuerriegel, Marina Elliott, K Lindsey Eaves, and Hannah Morris. (Image credit University of the Witwatersrand)

For, one unique aspect of the Rising Star Expedition was the technological innovation applied to communications within a remote environment. SEC cavers helped string cable throughout the cave and into the Dinaledi Chamber, enabling phone intercom communication at the top and base of the chute, as well as within the chamber (all linked to the Command Tent). Additionally, security cameras were placed along the 90m route at significant points to monitor progress on and off site. Within the chamber, no fewer than 3 cameras (including one that was easily movable) allowed those above to observe the careful recovery of fossil remains. These measures served for safety, as well as to allow instant communication with colleagues unable to reach the site in person. The usual process of dropping by one another’s pits while excavating to check progress and offer advice, was facilitated by way of virtual “tours” using the roving camera conveyed to a split-screen monitor in the Command Tent. These cameras and the attendant intermittent audio allowed for those above to post progress to social media, such as Twitter, to keep students, armchair paleoanthropologists, scientists, and curiosity seekers abreast of the goings-on below ground.

Advance underground scientists excavate the Dinaledi Chamber under the watchful eye of Lee Berger in the Command Tent. (Image by K Lindsay Hunter)

Meanwhile, in the chamber, team members first undertook a careful surface documentation and collection process to clear space to work. We quickly found that the clay-dirt floor was not only strewn with bones, but that they often lay just below the surface. We moved to a barefoot protocol and only with great trouble were able to clear a kind of path to an area towards the rear that seemed to have a particularly dense accumulation that included the outline of a cranium seen in what appeared to be sagittal view. This area came to be the focus of our work and was dubbed “the Puzzle Box,” as the bones closest to the surface were somewhat jumbled like puzzle pieces or interlaced like Jenga or Pick-up Stix. It lay under a low overhang of rock in a small space that then opened into the back of the chamber. It was often joked, “What idiot put the fossils in the passageway?!” It was within this tiny space that we would crouch day in and day out, using toothpicks (occasionally cave porcupine quills) and tiny paint brushes to uncover the remains within an approximately meter by meter square pit. Sediment was carefully collected using small plastic spoons.

Me taking a hard look at a fossil just excavated. (Image Credit: Rising Star Expedition)

Using methods modified for this unusual environment, mapping of the bones was accomplished using a handheld, 3D white light strobe scanner and standard documentation before extraction using a forensic camera and scale. Many of the bones were roughly the consistency of damp chalk and had to be carefully bagged before they were re-bagged with identification slips and then packed in bubble-wrap before being place in plastic containers that were re-packed in more bubble wrap and bundled in caving gear bags. These were then carefully hauled up the chute using a pulley system before being conveyed to the surface and then ultimately to the Science Tent for photographing, more detailed identification (something you don’t want to ask people using only headlamps to do), and preservation.

Peter Schmid documents fossils in the Science Tent, while John Hawks looks on. (Image K Lindsay Hunter)

For 21 days we carried on this intense routine, extracting more and more precious remains, far exceeding our original estimates of perhaps one skeleton. As the bones began to accrue in the Science Tent, so did a feeling that we were not dealing with a familiar species and that they had come to rest within the Dinaledi Chamber in an extraordinary way. Meal time and campfire chatter was dominated by speculation regarding these subjects, but everyone was hesitant to voice what was on all of our minds, and what ultimately was borne out by two years of research with a team of over 50 international scientists: in three weeks’ time, we had recovered more than 1200 remains (a 10 day excavation in March of 2014 increased the balance to over 1550 specimens) of a new species of Homo. A species that seemingly had come to be deposited within the chamber by intentional means, namely deliberate disposal by other hominins.

A revolutionary workshop was launched in May 2014, also advertised by social media, for early career researchers, who collaborated with over 30 colleagues from around the globe to describe the Dinaledi remains and place them in context. The two resulting primary papers Berger et al. and Dirks et al. were published in the open access journal eLife. These form the forward guard of scientific information on Homo naledi and are soon to be followed by a series of specialist papers on the various regions of the body, now under review. Armed with both a description and species diagnosis, as well as a thorough analysis of the geological context and taphonomy and preservation circumstances of the remains, Lee and the team formally introduced Homo naledi to the world on September 10, 2015 (almost 2 years to the day from the discovery) via a live-streamed press conference at Maropeng, the official visitor centre for the Cradle of Humankind World Heritage Site.

The announcement of the Homo naledi fossils took place at Maropeng under much fanfare. (Image Credit: University of the Witwatersrand)

The announcement and related papers gave the public and the scientific community at large its first glimpse of where this new species of Homo might swing from the branches of our extended family tree. Despite the plethora of material, however, our view on evolutionary placement is still somewhat unclear. Traditional methods of dating associated materials have been frustrated either by lack of availability or unsuitability of sediments, leaving the only recourse to date the bones directly, often a destructive enterprise. This has left Homo naledi without solid, radiometric dates for the time being, as scientists evaluate appropriate dating methods that produce the least damage to these valuable fossils. However, despite this, comparisons with known and well-dated species have led Berger et al. to hypothesize that the lineage to which these fossils belong may be quite old, possibly 2 to 2.5 million years in age. Depending on the ultimate dates, interpretation may change, though no matter how old they are, the Dinaledi remains have opened our eyes to the great diversity of hominin adaptation, even within the genus Homo.

It is quite apparent from the material that we are looking at a creature with a uniquely mosaic suite of characteristics. When we compare the H. naledi specimens to other hominin species, we see fascinating similarities, but also striking differences. In fact, one thing this material has shown us is how misleading species diagnoses based on very fragmentary material might be. If only a few portions of Homo naledi had been recovered and not in association, it would have been easy to mistake them for known species. However, taken as a whole, and across a wide spectrum of skeletal elements belonging to both sexes and all ages, we can see clearly that this is like nothing we have seen before.

The incredible fossils of Homo naledi, including a composite skeleton.(Image credit John Hawks, University of the Witwatersrand)

Were you to pass Homo naledi on the street, you would not confuse it for a fellow human. Though the shape of the skull is more rounded like ours, the very small brain is more in line with that of  Australopithecus, an early relative. The long and slender legs, as well, are similar to Homo, terminating in feet that are all but indistinguishable from yours or mine. However, added to this are unique features from both the shoulder and the hand that suggest Naledi was a proficient climber. The long, curved fingers, in particular, are reminiscent of those seen in arboreal, climbing nonhuman primates or australopithecines. The torso would have been bell-shaped or wider at the bottom to fit its flaring hips, giving it a more ape-like appearance. All of this begs the question: do the Dinaledi fossils occupy some intermediate space between the australopithecines and early Homo? And if so, do they lie along the path that led to us or to our extinct relatives? Only more time and more fossils will shed light on Naledi’s place within our increasingly convoluted evolutionary history.

Looking at the skulls of some of our own Genus shows the similarities, adn diferences. (Image by Chris Stringer. Public Domain)

With the announcement and the dissemination of these shocking findings, a powder keg of interest and criticism ignited (it’s only just now that I am able to take a breath and reflect a bit on what has come to pass). Scientific criticism (quickly documented in the press) immediately zeroed in on the assignment of a new species of Homo, the lack of solid dates, as well as the potentially humanlike behavior of deliberate disposal of its dead. This is completely to be expected. These are the most provocative and therefore, potentially vulnerable parts of the scientific argument carefully laid out in the two eLife papers. They are also some of the first areas that the scientists that have described them tackled: what do we have, how old is it, how did it get there? They are the first questions I would ask were I not a member of the scientific team. Each new taxa described must undergo this process of scrutiny, and behavioral interpretations in paleoanthropology are always met with no small amount of skepticism.

Rising Star and me on the news! (Credit NBC Nightly News, photo inset credit Elen Feuerriegel)

Not savoring the role of Dinaledi apologist, what must be understood, is that this same skepticism was the initial position of the Rising Star team members. No scientist wants to make an erroneous pronouncement that is quickly overturned or Flying Spaghetti Monster-forbid, a grossly inaccurate analysis that lands them on Retraction Watch. It makes absolutely no sense to rush and over-hype a find in the media to be torn to pieces by the scientific community. Remember, part of the initial success in funding came from Lee’s credibility and reputation for doing good science. Therefore, each aspect of the Homo naledi description and context was carefully scrutinized by scores of scientists, countless analytic comparisons made with the known hominin fossil record, and scenario after scenario examined and rejected. The Rising Star team has now put forward its best hypotheses given the data available to date, and it is placed at the feet not only of scholars, but anyone with an internet connection and a 3D printer.

Go ahead, examine the evidence yourself. The articles are free, as are 3D shapefiles for the attendant data. You can not only read the interpretations of our team, you can print it and touch it. If you are lucky enough to live in the Cradle area, you can visit Maropeng and see the original fossils lying in state, as well as speak to those (including me) who are related to the discovery. Draw your own conclusions, but please, do as we have done and examine all of the evidence first before a rush to judgment.

The beautiful hand of Homo naledi, with those long, grasping fingers. (Image credit John Hawks, University of the Witwatersrand)

As a member of the Rising Star team, I am proud of the work we have accomplished in just two years. We have shown that solid science can be performed in a relatively short period of time if one is able to cut through the bureaucracy and ego that normally bogs our field down. In many ways, Rising Star has been a practice in disruptive science, not only with regards to the phenomenal discoveries, but by consciously placing historically disadvantaged groups within the field in positions of power and responsibility: the primary excavation team was made up entirely of female scientists; the workshop and fossil analysis/description was performed largely by early career researchers of both sexes; the exploration team is composed of native South Africans from mixed ethnicities and educational backgrounds; and the primary articles were published open access in the journal eLife.

In this way, Homo naledi more resembles a comet than a star, “importing change of times and states” (Henry VI, Part 1, act 1, scene 1), but unlike a comet, expect this symbol of disruptive science in paleoanthropology to burn bright for some time to come.

Written by K. Lindsay Hunter (@Paleo_Bonegirl)

Edited by Jan Freedman (@JanFreedman)

Further reading:

Berger, L. R., et al, (2015), ‘Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa’, eLife, 4:e09560. [Full article]

Dirks, L. R., et al, (2015), ‘Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa’, eLife, 4:e09561. [Full article]

The Rising Star Team:

K Lindsey Hunter

Marina Elliott

Elen Feuerriegel

Alia Gurtov

Hannah Morris

Becca Peixotto

Criticisms to Homo naledi as a separate species:

• Jeffrey Schwartz suggests Homo naledi may be more than one species in Why the Homo naledi discovery may not be quite what it seems.
• Tim White suggests Homo naledi may just be a primative Homo erectus in Some bones to pick.
• John Hawks responds to these criticisms in Is Homo naledi just a primitive version of Homo erectus.

More reading on hominins:

Antón, S. C. 2003. ‘Natural history of Homo erectus.’. American Journal of Physical Anthropology. 122: pp.126–170. [Abstract only]

Berger, L. R., et al. 2010. ‘Austrlopithecus sedbia: a new species of Homo-like austraopith from South Africa.’ Science. 328 (5975) pp.195-204. [Abstract only]

Dirks, P. H. et al. (2010). ‘Geological setting and age of Australopithecus sediba from Southern Africa.’ Science. 328 (5975). pp.205-208. [Abstract only]

Ferring, R et al. 2011. ‘Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma.’ Proceedings of the National Academy of Sciences 108 (26): 10432. [Full article]

Kivell, T. L. et al. 2011. ‘Australopithecus sediba hand demonstrates mosaic evolution of locomotor and manipulative abilities.’ Science.  333 (6048). Pp.1411-1417. [Abstract only]

Schwartz, J., Tattersall, I. (2015). ‘Defining the genus Homo.’ Science. 349. pp.931-932. [Abstract only] DOI: 10.1126/science.aac6182

Skinner N, M, et al. (2015).’Human-like hand use in Australopithecus africanus.’ Science. 347 (6220) pp.395-399. [Abstract only]

Spoor, F., et al. 2007. ‘Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya.’ Nature 448 (7154): pp.688–691. [Abstract only]

Suwa G, et al. 2007. ‘Early Pleistocene Homo erectus fossils from Konso, southern Ethiopia.’ Anthropological Science. 115 (2): pp.133. [Abstract only]