2020 has been… quite the year! The pandemic changed a lot about the world including the ways in which paleoanthropologists, archaeologists, and…
In a year filled with lots of alarming anti-science news stories, we pause to acknowledge the positive news when we can. There has been a remarkable number of interesting discoveries announced related to the evolution of our species or primates in general. In fact, just as we were preparing to publish this guest post by Dr. Briana Pobiner and Ms. Ella Beaudoin from the Smithsonian Institution, National Museum of Natural History, the remainder of the skeleton of a human ancestor known colloquially as “Little Foot” (belonging to the genus Australopithecus, the same genus as the famed “Lucy” fossil) was finally revealed after 20 years of cleaning and excavation from the its embedding rock. Hope you enjoy reading. –JMO
Human evolution is an exciting, interdisciplinary science. We often think of fossils and artifacts as the only evidence for the grand narrative that is our evolutionary history, but just as important are discoveries based on genetics and living primates, as well as those that happen in museum collections: re-discovering new information from evidence that has already been unearthed. In this blog post, though, we’re going “back to basics” and highlighting (in chronological order) five discoveries published between May and August of 2017 of things that were actually dug up from the ground.
1) A new Homo naledi fossil nicknamed Neo
In 2015, an amazing discovery from deep inside a cave in South Africa was announced. An impressive suite of researchers led by Dr. Lee Berger from the University of Witwatersrand in South Africa, had recovered one of the largest assemblages of fossil hominins – and it was a new species called Homo naledi. What makes them so striking is their hodge podge of physical characteristics; for instance, Homo naledi has a more human like collarbone (clavicle), legs, ankles, and feet, while sharing some features of the hands and pelvis with earlier species like Australopithecus afarensis. This unique combination of modern and ancestral traits can be found across the Homo naledi fossils and led researchers to initially speculate that they could be up to 2 million years old, although the team didn’t have a secure date for the fossils when they were first published. But on May 9, 2017, the research team announced two important new findings in the journal eLife. The first is that even after Berger’s team recovered at least 15 individuals from the Dinaledi chamber of the Rising Star Cave System, they continued excavation in a second chamber in 2013 (the Lesedi chamber) and found 130 more fossils from 4 more individuals, including two adults and one child! One of the new fossils, a male nicknamed “Neo” after the Sesotho word for “gift”, is one of the most complete hominin fossils ever discovered. The second is that a combination of six different dating techniques – including radiometrically dating flowstones in the cave that covered some of the Homo naledi remains, as well as directly dating a few of their teeth – yielded a surprising result. Dated at between 236,000 and 335,000 years old, Homo naledi would have been sharing the planet with Homo erectus and Homo heidelbergensis, and even our own species, Homo sapiens. But this young age isn’t the most mysterious thing about these individuals. Researchers are still puzzled about how 19 individuals made their way into a complicated, dark, and treacherous cave system… while no other animal did. The Homo naledi individuals are the only fossils deposited within the cave, aside from one modern bird skeleton. Berger’s team thinks the most plausible explanation is that this group of hominins were deliberately disposing of their dead in a systematic way, by placing them deep within the cave system – yet other researchers think this would be a pretty sophisticated behavior for a hominin with a brain about half the size of ours. Since Berger’s team hasn’t found any other entrances to the cave system, and since the bones don’t have any of the tell-tale signs of being chewed on by carnivores, they think the chances that some kind of natural phenomenon accumulated a bunch of Homo naledi in two separate parts of the cave are pretty darn slim. And slim is what you have to be to actually get into the cave system! When Berger first realized how tricky it would be to investigate the caves, he put out a call for narrow-bodied archaeologists or paleontologists with caving experience to join his team – and he ended up choosing six women now dubbed the “underground astronauts”, the brave explorers that actually recover the Homo naledi fossils.
2) Ancient human DNA discovered in dirt
In a study led by Viviane Slon of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany and published in the journal Science on May 12, 2017, a team of evolutionary geneticists found lots of ancient DNA from mammals in sediments from caves in Europe and Asia. This discovery was extra cool because it didn’t even involve finding fossils, or artifacts, or anything we usually associate with the past. Instead, researchers found ancient human DNA in… dirt! What?? While that sounds like something out of a science fiction novel, it really happened. The paleo-geneticists collaborated with several groups of archaeologists excavating in caves in Belgium, Croatia, France, Russia, and Spain with known early human occupation and collected 85 sediment samples from seven archaeological sites varying in age between about 14,000 and 550 thousand years ago. They found fragments of mitochondrial DNA from twelve different families of mammals in the sediments, including DNA from extinct animals like woolly mammoths, woolly rhinos, cave hyenas, and cave bears. Most exciting was the discovery of ancient human DNA in nine of those 85 samples from four of the sites: eight had Neanderthal DNA, and one had Denisovan DNA. In some cases, the researchers can even tell from the specific DNA sequences that they come from more than one individual! This discovery could be a real game-changer for human evolution research, as it allows us to identify the presence of hominins at prehistoric sites and in layers where their fossils haven’t even been found. For instance, this pushed back the known hominin (early human) occupation of Denisova Cave in Siberia by tens of thousands of years. It also demonstrates that it is possible to extract DNA from samples stored at room temperature for several years – like those collected previously for dating, understanding site formation processes, or reconstructing ancient environments.
3) Homo sapiens fossils from Morocco that are over 300,000 years old!
In 1961, miners stumbled upon a nearly complete fossil human skull in Jebel Irhoud, Morocco, sparking a decades-long journey to understand who these individuals were and what their place was in our evolutionary story. Paleoanthropologist Jean-Jacques Hublin at the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany, started new excavations of the cave in 2004 hoping to date the little bit of remaining sediment still in place and tie them to the layers where fossils were found in the original excavations. In 2007, researchers from Hublin’s team published a date of 160,000 years for a juvenile mandible from this site called Jebel Irhoud 3 based on radiometric dating (uranium series/electron spin resonance) of one of its teeth. As research continued, Hublin’s team uncovered not only sediment they could date but many new human fossils including teeth, jaws, partial skulls, and arm and leg bones from at least five individuals including an adolescent and a child – bringing the total number of individuals at the site to 22! The new human fossils were mainly found in a single layer that also contained butchered animal bones and burned flint stone tools which indicated that they had control of fire and allowed the team to estimate the age of the tools using thermoluminescence dating. On June 8, 2017, the team announced that the new fossils were between about 280,000 and 350,000 years old! This date jibes with the team’s new date for the Jebel Irhoud 3 mandible (using improved radiometric dating) of 254,000 to 318,000 years old – and is about 50% older than the previously known oldest Homo sapiens fossils from Omo Kibish, Ethiopia, dated at about 195,000 years old. Like Neanderthals, the faces, teeth, and lower jaws of these Moroccan fossils look more modern or specialized, while their braincases have more ancestral features like an elongated shape. The team suggests that this group of early Homo sapiens was not necessarily the ancestors of us all but rather part of a large, pan-African population that over time evolved into modern humans.
4) Humans arrived in Australia 65,000 years ago
The earliest peopling of Australia has long been a fascinating and sometimes contentious question. Estimates from previous research were that Homo sapiens arrived in Australia by about 47,000 years ago, and possibly as long ago as 60,000 years ago. On July 19, 2017, Dr. Chris Clarkson and his team from the University of Queensland announced in the journal Nature results of a new excavation at an aboriginal rock shelter called Madjedbebe which pushed back human occupation of Australia to 65,000 years ago! While this site had been excavated in the 1970s, new digs in 2012 and 2015 recovered over ten thousand new artifacts from the site, including the earliest known edge-ground axes (stone axes that would have had handles). The site had been previously radiocarbon dated, but radiocarbon cannot accurately date sediments older than roughly 50,000 years. Clarkson’s team used optically stimulated luminescence (or OSL) dating on 52 samples of the sediments surrounding lithic artifacts in the deepest layers to get the new ancient dates. Using multiple dating techniques, they showed that the range of artifact deposits at the site ranged from 10,000 years ago all the way back to 65,000 years ago. They also conducted extensive studies of the stone tools to try and understand the technological advancement of these early native Australian settlers, examined ancient plant remains preserved at the site to understand what plants people may have been eating, and analyzed the size distribution of sediment grains to investigate the ancient soils. All these methods came together to tell the story of a people grinding a variety of foods including seeds, fruits, other plants, and animals, eating nuts and yams, making ochre “crayons”, and using reflective pigment 65,000 years ago in northern Australia. Importantly, this find overturns the hypothesis that Homo sapiens drove the megafauna of Australia to extinction soon after they arrived on the continent, since climate and fossil data show a decline in Australian megafauna at 45,000 to 43,100 years ago, well after the new evidence for human arrival. Researchers excavating the site worked closely with the local aboriginal community in an effort to acknowledge the importance of this site and to make sure the ownership and stewardship of the site stayed with its ancestral people. The University of Queensland and the Gundjeihmi Aboriginal Corporation worked together to give final say over the excavation and the artifacts to the Mirarr, who are the traditional owners of the site.
5) A new species of ancient ape, Nyanzapithecus alesi
In a publication in Nature on August 10, 2017, Dr. Isaiah Nengo, Turkana Basin Institute, and De Anza College and his team from the National Museums of Kenya introduced the world to “Alesi”. Alesi is an infant ape skull, roughly the same size as a baseball, but with a big impact! This 13 million year old skull, found in the Napudet area west of Lake Turkana in northern Kenya, is from a new species named or Nyanzapithecus alesi and represents a time that researchers know very little about: when the last common ancestors of modern humans and all other living apes were around. While bits and pieces of fossil apes have been found over the years, this is one of the only intact skulls. This makes Alesi not only incredibly rare, but also incredibly useful. Skulls give us detailed insight into brain size – from the size of the cranium, the age the individual was when it died and what it ate – from the teeth, as well as vision and hearing – from the eye sockets and small ear bones. Researchers got not just one, but two important dates from this amazing find. The first is the time in earth’s history during which this small individual was alive: roughly 13 million years ago, determined from dating volcanic minerals surrounding the fossil. The second is how old the individual was when it died: about 16 months old, determined by using specialized X-ray technology at the European Synchrotron Radiation Facility in Grenoble, France. The synchrotron can scan and count the growth rings in Alesi’s unerupted teeth to figure out how long this baby ape had been growing when a nearby volcano buried her along with the forest she lived in, much like how scientists can count tree rings to determine how long a tree has been growing. It was the synchrotron scans of the unerupted adult teeth and ear canals that clinched the identification of the fossil as a nyanzapithecine – an extinct sister group to humans, great apes, and gibbons.
Edited by Jason Organ, PhD, Indiana University School of Medicine.
(Featured image at the top of this post courtesy of Max Planck Institute for Evolutionary Anthropology)