Rethinking Human Evolution: The Discovery of Homo naledi

By Kristin Foss

 Today, modern humans (Homo sapiens) are the only species alive in their genus. However, a recent discovery in South Africa has revealed that the human ancestor family is a little bigger than previously thought, rocking the field of human evolution. Recently, Berger et al. 2015 reported on the new discovery of the extinct species, Homo naledi, discovered in the Dinaledi Chamber of the Rising Star cave system in South Africa. Over 1,500 fossils have been excavated from the site, all belonging to at least 15 individuals.

“This is unprecedented in paleoanthropology. The fossils are different from anything that has been previously been found. We knew we were making history,” said Dr. Juliet Brophy, a Rising Star expedition paleoanthropologist and professor in the Department of Geography and Anthropology at Louisiana State University. The recent discovery reveals how much there is still to learn about human evolution and mystery behind the ancient human lineage tree.

Over 1,500 fossils have been excavated from the Rising Star cave system in South Africa. Photo Credit: Berger et al. 2015/ Source: ElifeSciences

Over 1,500 fossils have been excavated from the Rising Star cave system in South Africa. Photo Credit: Berger et al. 2015/ Source: ElifeSciences

After years of analysis, the work of experts and early career paleoanthropologists have resulted in the first publications describing the new species, Homo naledi. Like other human ancestors (Homo genus), this species is characterized by a similar body size and mass, but the small head and brain size is unique to the extinct genus of Australopithecus. In the study of human evolution, paleoanthropologists study the taxonomic, primate family Hominidae, especially these two accepted, common genera: Homo and Australopithecus. Humans belong to the genus Homo. But Australopithecus is an extinct genus, with both ape and human characteristics such as apelike facial features, small brains, and long, strong arms.

From broken pieces and disconnected fossils from the Rising Star cave, researchers were able to determine that this indeed was a new species. Paleoanthropologists studied all aspects of the body ranging from feet, skull, hands, and even teeth. “Teeth are incredibly informative, and they can help answer what species it is, diet, behavior, [and even] where it lived,” said Brophy. As a part of the Rising Star Expedition, her research reveals that the square-like shape of the premolar teeth does not overlap with any other human ancestor studied, indicating a new species.

However, when examining the torso region of the species, Dr. Caroline VanSickle, a post-doctoral scholar of Feminist Biology at the University of Wisconsin-Madison, and her team thought the fossils indicated findings similar to previously discovered specimens. Due to the wide pelvis, cone-shaped rib-cage and the small spine, the team initially thought they had an Australopithecus species. “[But] when we compared our results with other [teams], we quickly realized that no species of Australopithecus had such a human-looking foot, long legs, small teeth, or a more Homo looking cranium. It was truly a team effort to rule of the possibility that this was any known species,” said Dr. VanSickle.

Sections of mandible fossils of Homo naledi Photo Credit: Berger et al 2015/ Source:ELifeSciences

Sections of mandible fossils of Homo naledi Photo Credit: Berger et al 2015/ Source:ELifeSciences

 Due to the difficult location of the fossils, a team of trained, small scientists, later called the “Underground Astronauts,” excavated the Dinaledi chamber of the Rising Star cave system for three weeks. Two of the six Underground Astronauts included Elen Feuerriegel, a PhD candidate at the Australian National University, and K. Lindsay Hunter, a biological anthropologist.

Split into shifts (3-6 hours), teams of two to three advance cave scientists descended into the caves, where one to two individuals excavated the site and one scientist recorded. “Each work shift in the site began with a fresh 3D scan of the active excavation areas,” Feuerrigel said. To prevent the potential crushing of fossil material, “in effect, every shift began with a peculiar kind of spider-like moon walk around the site… before we could eventually position ourselves and get down to the nitty-gritty of excavating. It was deceptively hard work,” Feuerrigel said.

A view of command central set up at the entrance of the Rising Star Expedition cave in South Africa. Photo credit: Simon Fraser University/ Source: Flickr

A view of command central set up at the entrance of the Rising Star Expedition cave in South Africa.
Photo credit: Simon Fraser University/ Source: Flickr

Afterwards, all fossils were photographed, given unique specimen and photograph numbers, given initial assessments, bubble wrapped and placed into Tupperware containers for their safe trip back to the surface. “Working underground, you get a quick and dirty impression of the bone ID, but we didn’t want to handle them too much in the dark,” said Hunter. “[But once out of the cave] we followed the fossils into the Science Tent to see them unwrapped, photographed, and to get a better look at them.”

The success of the expedition was a team effort not only including the Underground Astronauts excavating the fossils, but the scientists above ground cataloging and the teams of expert paleoanthropologists who would further study these new specimens. “It was incredibly enriching, both professionally and personally, to be in close contact with so much expertise and so many excellent people,” said Feuerrigel. “ It made for some of the most interesting dinner table conversation I’ve ever had!”

After the fossils were removed, subsequent workshops were held at the University of Witwatersrand in South Africa where experts from across the globe worked for a month to solve the mystery of these new fossils. Akin to a giant think tank, the workshops divided scientists into teams and tackled the 1,500+ fossils, said Brophy. “We all got along extremely well. We were so full of excitement and intrigue that it would have been impossible not to be in a good mood,” said Brophy.

Dr. VanSickle summed up how this discovery is important and unique in four points.

First, with fossils from at least 15 different individuals of varying ages, this is a huge sample of bones from a single site. In contrast, finding hominin fossils is usually incredibly rare, and in other cases entire sites will be completely excavated only to uncover one or two bones.

Hands of the homo naledi Photo Credit: Berger et al. 2015/ Source:ElifeSciences

Hands of the homo naledi
Photo Credit: Berger et al. 2015/ Source:ElifeSciences

Second, Homo naledi is “totally unpredictable in how it looks,” VanSickle said. There isn’t an exact date yet for when Homo naledi lived, but it makes paleoanthropologists realize there is more complexity to human evolution.

Third, there’s the entire mystery of how these individuals ended up in the darkest area of the cave. Homo naledi were small brained, small bodied individuals, and there is no evidence that these creatures either fell or were dragged by carnivores. There was no evidence of additional entrances. Therefore, this leaves the scientists to hypothesize that “they intentionally deposited dead bodies in this hard-to-reach cave, a behavior that we would likely assign to some sort of ritual value [like Homo sapiens],” said Van Sickle.

Lastly, the open access research aspects of this project were crucial to all scientists. From publishing in an open access journal (Berger et al. 2015 and Dirks et al. 2015) to setting up a MorphoSource, a site where scans of the fossils are available for everyone, science communication was at the forefront. These sites not only provide easy access to the findings and evidence to anyone worldwide, but it allows other scientists to conduct their own analysis on the fossils and test their own conclusions, said VanSickle. All without having to book a flight to South Africa to see the original fossils.

The Rising Star Expedition isn’t over just yet. Scientists are continuing to analyze samples and many new research projects are to be undertaken. “We have only scratched the surface in terms of the research on the Rising Star,” Brophy said.

*Special thanks to Dr. Juliet Brophy, Dr. Caroline VanSickle, Elen Feuerrigel, and K. Lindsay Hunter for their time and willingness to allow me to interview them for this article.

Sources:

Berger, Lee R., et al. “Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.” eLife 4 (2015): e09560.

Dirks, Paul HGM, et al. “Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa.” eLife 4 (2015): e09561.

http://morphosource.org/

http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-afarensis

http://humanorigins.si.edu/education/intro-human-evolution

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s