Lee Berger has recently discovered the bones of numerous ancient human relatives called “Homo naledi,” a hominid which “appears to have buried its dead”. In the Rising Star Cave (also known as the Westminster or Empire Cave) in the Malmani dolomites in South Africa, at least 1,550 remnants of infant, children, adult, and elderly fossilized hominid bones have been found, different than the fossils the archeological world has found previously, which is the topic of this sample essay.

Discovery of a New Human Species "Homo Naledi"

Rising Star Cave is close the “Cradle of Humankind” World Heritage site in Swartkrans, Krugersdorp, 30 kilometers or 20 miles northwest of Johannesburg. Lee Berger is a paleoanthropologist who has discovered many fossils; lately with his nine-year-old son. The pair discovered Australopithecus sediba in 2008, the two-million-year-old fossils of an adult female and young male which “may be one of humankind’s oldest ancestors”.

A pair of local South African cavers led Berger to the Rising Star Cave in 2013, leading him to a narrow passage that required recruitment of “skinny” scientists in order to navigate. The most important aspect of Berger’s discovery is the burial behavior of Homo naledi, since pre-human ancestors were thought not to bury their dead. 

More missing links

Shreeve noted that the cavers had to use a maneuver called “superman’s crawl” to navigate the tight spaces; “holding one arm tightly against the body and extending the other above the head,” like Superman in flight.

Lee Berger dogged determination to find more interesting fossils in South Africa instead of the Rift Valley has finally paid off after 20 years of work. There is a gap in human evolution which lies between two million and three million years ago; between Lucy, an Australopithecus afarensis discovered in 1974 in Ethiopia, and Homo erectus, our upright-walking, “tool-wielding, fire-making, globe-trotting” ancestor who looks much like humans do today.

The bipedal and increased brain function that occurred during the dark million years cannot be fully understood until the missing link is found. The fossil records found to date only include Homo habilis, named “handy man” by Louis Leakey in 1964 due to its use of stone tools found in Olduvai Gorge, Tanzania. But before H.habilis there are no records until Lucy appears on the timeline. The scientists’ find clearly demonstrated that H. Naledi was part of the puzzle of modern humankind. 

Crawling into the cave

After Lee Berger confirmed the presence of the bones the cavers had assured him were there, he quickly realized that it would take a special type of person to fit through the narrow entrance to the cave – a space that was only 8 inches wide in places. Using social media, he recruited for the position stating that he needed skinny individuals who were “willing to work in cramped quarters,” and got 60 applicants.

Berger chose the six most qualified applicants, all women, whom he dubbed “underground astronauts”. With funding from National Geographic, an “aboveground command center, a science tent, and a small village of sleeping and support tents” were established outside the cave, and “two miles of communication and power cables” twisted their way down into the cave source of the fossils.

Cameras allowed team members up top to view the cave clearly, and a graduate student from Simon Fraser University in British Columbia named Marina Elliott was the first scientist into the cave. Of the cave opening, Marina stated, “It was like looking down into a shark’s mouth. There were fingers and tongues and teeth of rock” which she feared might injure her. Working in two-hour shifts, Elliott and the other five scientists plotted and bagged 400 plus fossils just on the surface of the chamber.

The bones were densely packed since the bodies were probably thrown on top of one another, and only six inches down into the soil did the fossils finally stopped presenting themselves to the scientists. At least 15, maybe more full hominid skeletons were found, including a range of ages and even tiny inner ear bones; the bones ranged in appearance from seemingly ancient to “astonishingly modern” providing no doubt that H. Naledi was part of the connection between Lucy and H. Habilis.

Homo Naledi vs. modern humans

On September 10th, 2015, a group of researchers and paleontologists published Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa,” a detailed account of the differences and similarities between humankind and Homo naledi". In the document, the authors state that Homo naledi is

“characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths,” relating the human bone finds to Lucy.

The paper goes ont to discuss the similarity of Homo naledi to Homo erectus, Homo habilis, and Homo rudolfensis. H. naledi has a “humanlike foot and lower limb” as well as “humanlike manipulatory adaptations of the hand and wrist”. These very human aspects of H. naledi appear in tandem with the postcrania, “australopith-like trunk,” pelvis, shoulder, and proximal femur, of which the 15 individual skeletons found are representative.

Determining the Age of Fossilized Bones

Yong noted that the paleontologist team does not yet know exactly or even approximately how old the bones found in the Rising Star Cave are, at least not definitively. He also noted that “without that age, it’s hard to know how Homo naledi fits into the story of human evolution,” much less how to determine the reason for the distinctive burial behaviors that Lee Berger links to modern humans.

Yong noted that “dating fossils is really difficult” and spoke with a biologist at the University of Wisconsin in order to determine exactly how difficult it is. There are three methods of dating fossils: carbon dating, DNA extraction, electron spin resonance (ESR), observing nearby fossils, and observing the nearby landscape. These are currently the only ways to determine the approximate or specific age of a fossil or bone from a much earlier time period. In order to understand the extreme difficulty of dating fossils, an in-depth discussion of these methods follows below.

Carbon dating is the most well-known method of the five, and involves measuring the amount of carbon-14 left in a specimen (carbon-14 is a radioactive carbon isotope that gradually gathers in the bodies of animals and humans throughout life, and decays very gradually after death). The juxtaposition of the amount of carbon left and the amount of carbon gathered allows for an approximate dating of the fossil in question. However, since carbon-14 decays “relatively quickly,” according to Yong, this method does not work well for fossils that are older than 50,000 years prior to modern humankind.

Since carbon-dating effectively destroys the fossils, the paleontologist team wanted to refrain from using carbon dating until a “description of the species” had been officially published. It is likely that carbon-dating might be employed in the future to determine the age of the fossils, or as Christ Stinger from the Natural History Museum of London noted, “to test whether the material lies beyond the effective range of that method”.

The next step for the team might be to attempt a DNA extraction from the fossils; however the wet, warm environment of the Rising Star Cave in South Africa may prevent this method from being effective, as it is usually most effective in an arid and very cold environment. John Hawks, a biologist at the University of Wisconsin, stated,

“but the bones are exceptionally preserved, so if there’s a chance of finding ancient DNA anywhere in southern Africa, it’s here”.

Electron spin resonance, or ESR is worthwhile method for tooth fossil dating, and involved radiation in order to determine the levels of radiation in the natural environment where the tooth was found, and how long it was buried before being located. This technique uses a higher-energy state of electrons inside deposits like underground uranium on the teeth themselves, and helps scientists deduce the age of the teeth.

This method can be very labor intensive, noted Hawks, and involves “installing actual radiation dosimeters and take out vertical cores of sediment” from the dig site. The ESR samples are also usually “cross-checked” against other data sources, such as carbon-dating in order to confirm the findings, and so are reliant upon a second source of corresponding data.

Looking at the environment a fossil was found in is another way to determine its age. Companions in death, including other people, animals, and plants is a consistently reliable method, and delving into the contents of the surrounding environment for other age clues is another. East Africa’s landscape is comprised of layers and layers of rock, accumulated over millions of years. These layers include volcanic ash, among other things; scientists can date the layers by “measuring radioactive isotopes of potassium” inside of them.

This method is a similar technique to carbon-dating, but it makes the age of fossils that are much older more available. The problem facing scientists in relation to the use of this technique and Homo naledi is that the bones in this case were not buried deeply in sediment, but remained nearly at the top of the sediment layer on the floor of the cave for millions of years. Thus the layers cannot be excavated to determine the age of the fossils.

The word for this cave sediment is “breccia,” which Yong defined as “a concrete-like mixture of gravel, sand, and other junk that accumulated [on] the floor of the cave.” Inside caves, calcite formations called flowstones are created as water drips down the walls or across the floors of caves. Flowstones are made up of soluble uranium which eventually decays into the elements of lead and thorium.

If both the breccia and flowstones are in close proximity to the fossils, Hawks stated that “you’ve got a bracket for age” of the fossils. Another issue with Homo naledi is that there is no breccia to help scientists date the fossils, but a softer, less rigid sediment. The team has not yet dug down to find out if there are flowstones underneath the fossils, but there are flowstones over the fossils. This type of dating is necessary to determine the outer time limit for the fossils, or the maximum age, so it is yet to be determined whether or not this can be done with Homo naledi. The paleontologist team will use radar to form an image of the cave floor and determine where the very lowest samples can be taken; “they could be millions of years apart,” Hawks said.

Another method for dating is to look at the alignment of magnetic minerals such as iron in the sediments surrounding the fossils; their alignment, which has changed at various times during history, helps scientists determine the date of the sediments. This technique is very slow-going and takes a long time to perform, however. All fossil dating methods rely strongly on the luck of the location and time of fossil preservation, as well as painstaking research and measuring work that may or may not prove fruitful in the end.

For this reason, it may some time before a date is assigned to Homo naledi; in the meantime the public continues to be fascinated by the find. The paleontologist team working on the fossils has stated, “We’re committed, as a team, to not publish a date estimate until we have multiple estimates that arrive at the same result,” meaning that there will be no fast and hard answer until multiple tests and dating techniques have been tried, either succeeding or failing. The world will have to wait for Homo naledi’s exact age and position in the timeline of human history.

References

“Lee Berger Paleoanthropologist.” National Geographic. National Geographic Society, 2015. 18 September 2015.

Berger, Lee R., Hawks, John, de Ruiter, Darryl J., Churchill, Steven E., Schmid, P., Delezene, Lucas K., . . . Zipfel, Bernhard. “Homo Naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.” eLife 4:e09560 (2015): n. pag. Web. 10 September 2015.

Howley, Andrew. “Homo Naledi’s Powerful Hand Up Close.” National Geographic. National Geographic Society, 2015. 16 September 2015.

McKenzie, David, & Wende, Hamilton. “Homo Naledi: New Species of Human Ancestor Discovered in South America.” CNN. Cable News Network, 2015. 10 September 2015.

Shreeve, Jamie. “This Face Chages the Human Story. But How?” National Geographic. National Geographic Society, 2015. 10 September 2015.

Wilford, John Noble. “Homo Naledi, New Species in Human Lineage, is Found in South African Cave.” New York Times. The New York Times Company, 2015. 10 September 2015.

Yong, Ed. “Why Don’t We Know the Age of the New Ancient Human?” The Atlantic. The Atlantic Monthly Group, 2015. 14 September 2015.