Seven New Things We Learned About Human Evolution in 2021

This year—2021—has been a year of progress in overcoming the effects of the Covid-19 pandemic on human evolution research. With some research projects around the world back up and running, we wanted to highlight new and exciting discoveries from 13 different countries on five different continents. Human evolution is the study of what links us all together, and we hope you enjoy these stories we picked to show the geographic and cultural diversity of human evolution research, as well as the different types of evidence for human evolution, including fossils, archaeology, genetics, and even footprints!

New Paranthropus robustus fossils from South Africa show microevolution within a single species.

The human fossil record, like any fossil record, is full of gaps and incomplete specimens that make our understanding of complex evolutionary trends difficult. Identifying species and the process by which new species emerge from fossils falls in the realm of macroevolution, or evolution over broad time scales. These trends and changes tend to be more pronounced and easier to identify in the fossil record; think about how different a Tyrannosaurus rex and a saber-toothed cat are from each other. Human evolution only took place over the course of 5 to 8 million years, a much shorter span compared to the roughly 200 million years since dinosaurs and mammals shared a common ancestor. Because of this, smaller-scale evolutionary changes within a single species or lineage over time, called microevolution, is often difficult to detect.

Fossils of one early human species, Paranthropus robustus, are known from multiple cave sites in South Africa. Like other Paranthropus species, P. robustus is defined by large, broad cheeks, massive molars and premolars, and a skull highly adapted for intense chewing. Fossils of P. robustus from Swartkrans cave, just 20 miles west of Johannesburg, are dated to around 1.8 million years ago and show a distinct sagittal crest, or ridge of bone along the top of the skull, with their jaws indicating a more efficient bite force. Newly discovered fossils of P. robustus from Drimolen cave, about 25 miles north of Johannesburg, described by Jesse Martin from La Trobe University and colleagues in January, are at least 200,000 years older (2.04-1.95 million years old) and have a differently positioned sagittal crest and a less efficient bite force, among other small differences. Despite numerous disparities between fossils at the two sites, they much more closely resemble each other than any other known species of hominin. Because of this, researchers kept them as the same species from two different time points in a single lineage. The differences between fossils at the two sites highlight microevolution within this Paranthropus lineage.

Fossil children from Kenya, France, and South Africa tell us how ancient and modern human burial practices changed over time.

Most of the human fossil record includes the remains of adult individuals; that’s likely because larger and thicker adult bones, and bones of larger individuals, are more likely to survive the burial, fossilization, and discovery processes. The fossil record also gets much richer after the practice of intentional human burial began, starting at least 100,000 years ago.

In November, María Martinón-Torres from CENIEH (National Research Center on Human Evolution) in Spain, Nicole Boivin and Michael Petraglia from the Max Planck Institute for the Science of Human History in Germany, and other colleagues announced the oldest known human burial in Africa—a two-and-a-half to three-year-old child from the site of Panga ya Saidi in Kenya. The child, nicknamed “Mtoto” which means “child" in Kiswahili, was deliberately buried in a tightly flexed position about 78,000 years ago, according to luminescence dating. The way the child’s head was positioned indicates possible burial with a perishable support, like a pillow. In December, a team led by University of Colorado, Denver’s Jaime Hodgkins reported the oldest known burial of a female modern human infant in Europe. She was buried in Arma Veirana Cave in Italy 10,000 years ago with an eagle-owl talon, four shell pendants, and more than 60 shell beads with patterns of wear indicating that adults had clearly worn them for a long time beforehand. This evidence indicates her treatment as a full person by the Mesolithic hunter-gatherer group she belonged to. After extracted DNA determined that she was a girl, the team nicknamed her “Neve” which means “snow” in Italian. Aside from our own species, Neanderthals are also known to sometimes purposefully bury their dead. In December, a team led by Antoine Balzeau from the CNRS (the French National Centre for Scientific Research) and Muséum National d’Histoire Naturelle in France and Asier Gómez-Olivencia from the University of the Basque Country in Spain provided both new and re-studied information on the archaeological context of the La Ferrassie 8 Neanderthal skeleton, a two-year-old buried in France about 41,000 years ago. They conclude that this child, who is one of the most recently directly dated Neanderthals (by Carbon-14) and whose partial skeleton was originally excavated in 1970 and 1973, was purposefully buried. There have also been suggestions that a third species, Homo naledi, known from South Africa between about 335,000 and 236,000 years ago, purposefully buried their dead—though without any ritual context. In November, a team led by University of the Witwatersrand’s Lee Berger published two papers with details of skull and tooth fragments of a four to six-year-old Homo naledi child fossil, nicknamed “Leti” after the Setswana word “letimela” meaning “the lost one.” Given the location of the child’s skull found in a very narrow, remote and inaccessible part of the Rising Star cave system, about a half mile from Swartkrans, this first partial skull of a child of Homo naledi yet recovered might support the idea that this species also deliberately disposed of their dead.

The first Europeans had recent Neanderthal relatives, according to genetic evidence from Czechia and Bulgaria.

Modern humans, Homo sapiens, evolved in Africa and eventually made it to every corner of the world. That is not news. However, we are still understanding how and when the earliest human migrations occurred. We also know that our ancestors interacted with other species of humans at the time, including Neanderthals, based on genetic evidence of Neanderthal DNA in modern humans alive today—an average of 1.9 percent in Europeans.

Remains of some of the earliest humans in Europe were described this year by multiple teams, except they were not fully human. All three of the earliest Homo sapiens in Europe exhibit evidence of Neanderthal interbreeding (admixture) in their recent genealogical past. In April, Kay Prüfer and a team from the Max Planck Institute for the Science of Human History described a human skull from Zlatý kůň, Czechia, dating to around 45,000 years old. This skull contains roughly 3.2 percent Neanderthal DNA in the highly variable regions of the genome, comparable with other humans from around that time. Interestingly, some of these regions indicating Neanderthal admixture were not the same as modern humans, and this individual is not directly ancestral to any population of modern humans, meaning they belonged to a population that has no living descendants. Also in April, Mateja Hajdinjak and a team from the Max Planck Institute for Evolutionary Anthropology described three similar genomes from individuals found in Bacho Kiro Cave, Bulgaria, dating between 46,000 and 42,000 years old. These individuals carry 3.8, 3.4, and 3.0 percent Neanderthal DNA, more than the modern human average. Based on the distribution of these sequences, the team concluded that the three individuals each had a Neanderthal ancestor only six or seven generations back. This is roughly the equivalent length of time from the turn of the twentieth century to today. Interestingly, these three genomes represent two distinct populations of humans that occupied the Bulgarian cave—one of which is directly ancestral to east Asian populations and Indigenous Americans, the other of which is directly ancestral to later western Europeans. These findings suggest that there is continuity of human occupation of Eurasia from the earliest known individuals to present day and that mixing with Neanderthals was likely common, even among different Homo sapiens populations.

A warty pig from Indonesia, a kangaroo from Australia, and a conch shell instrument from France all represent different forms of ancient art.

Currently, the world’s oldest representational or figurative art is a cave painting of a Sulawesi warty pig found in Leang Tedongnge, Indonesia, that was dated to at least 45,500 years ago using Uranium series dating—and reported in January by a team led by Adam Brumm and Maxime Aubert from Griffith University. In February, a team led by Damien Finch from the University of Melbourne in Australia worked with the Balanggarra Aboriginal Corporation, which represents the Traditional Owners of the land in the Kimberly region of Australia, to radiocarbon date mud wasp nests from rock shelters in this area. While there is fossil evidence of modern humans in Australia dating back to at least 50,000 years ago, this team determined that the oldest known Australian Aboriginal figurative rock paintings date back to between around 17,000 and 13,000 years ago. The naturalistic rock paintings mainly depict animals and some plants; the oldest example is of a about 6.5 footlong kangaroo painting on the ceiling of a rock shelter dated to around 17,300 years ago. Right around that time, about 18,000 years ago, an ancient human in France cut off the top of a conch shell and trimmed its jagged outer lip smooth so it could be used as the world’s oldest wind instrument. A team led by Carole Fritz and Gilles Tostello from the Université de Toulouse in France reported in February that they re-examined this shell, discovered in Marsoulas Cave in 1931, using CT scanning. In addition to the modifications described above, they found red fingerprint-sized and shaped dots on the internal surface of the shell, made with ochre pigment also used to create art on the walls of the cave. They also found traces of a wax or resin around the broken opening, which they interpreted as traces of an adhesive used to attach a mouthpiece as found in other conch shell instruments.

Fossil finds from China and Israel complicate the landscape of human diversity in the late Pleistocene.

This year a new species was named from fossil material found in northeast China: Homo longi. A team from Hebei University in China including Qiang Ji, Xijun Ni, Qingfeng Shao and colleagues described this new species dating to at least 146,000 years old. The story behind the discovery of this cranium is fascinating! It was hidden in a well from the Japanese occupying forces in the town of Harbin for 80 years and only recently rediscovered. Due to this history, the dating and provenience of the cranium are difficult to ascertain, but the morphology suggests a mosaic of primitive-like features as seen in Homo heidelbergensis, and other more derived features as seen in Homo sapiens and Neanderthals. Although the cranium closely resembles some other east Asian finds such as the Dali cranium, the team named a new species based on the unique suite of features. This newly named species may represent a distinct new lineage, or may potentially be the first cranial evidence of an enigmatic group of recent human relatives—the Denisovans. Adding to the increasingly complex picture of late Pleistocene Homo are finds from Nesher Ramla in Israel dating to 120,000 to 130,000 years old, described in June by Tel Aviv University’s Israel Hershkovitz and colleagues. Like the Homo longi cranium, the parietal bone, mandible and teeth recovered from Nesher Ramla exhibit a mix of primitive and derived features. The parietal and mandible have stronger affiliations with archaic Homo, such as Homo erectus, while all three parts have features linking them to Neanderthals. Declining to name a new species, the team instead suggests that these finds may represent a link between earlier fossils with “Neanderthal-like features” from Qesem Cave and other sites around 400,000 years ago to later occupation by full Neanderthals closer to 70,000 years ago. Regardless of what these finds may come to represent in the form of new species, they tell us that modern-like traits did not evolve simultaneously, and that the landscape of human interaction in the late Pleistocene was more complex than we realize.

The ghosts of modern humans past were found in DNA in dirt from Denisova Cave in Russia.

Denisova Cave in Russia, which has yielded fossil evidence of Denisovans and Neanderthals (and even remains of a 13-year-old girl who was a hybrid with a Neanderthal mother and Denisovan father), is a paleoanthropological gift that keeps on giving! In June, a team led by Elena Zavala and Matthias Meyer from the Max Planck Institute for Evolutionary Anthropology in Germany and Zenobia Jacobs and Richard Roberts from the University of Wollongong in Australia analyzed DNA from 728 sediment samples from Denisova Cave—the largest analysis ever of sediment DNA from a single excavation site. They found ancient DNA from Denisovans and Neanderthals… and modern humans, whose fossils have not been found there, but who were suspected to have lived there based on Upper Paleolithic jewelry typically made by ancient modern humans found in 45,000-year-old layers there. The study also provided more details about the timing and environmental conditions of occupation of the cave by these three hominin species: first Denisovans were there, between 250,000 and 170,000 years ago; then Neanderthals arrived at the end of this time period (during a colder period) and joined the Denisovans, except between 130,000 and 100,000 years ago (during a warmer period) when only Neanderthal DNA was detected. The Denisovans who came back to the cave after 100,000 years ago have different mitochondrial DNA, suggesting they were from a different population. Finally, modern humans arrived at Denisova Cave by 45,000 years ago. Both fossil and genetic evidence point to a landscape of multiple interacting human species in the late Pleistocene, and it seems like Denisova Cave was the place to be!

Fossilized footprints bring to light new interpretations of behavior and migration in Tanzania, the United States and Spain.

Usually when we think of fossils, we think of the mineralized remnants of bone that represent the skeletons of long since passed organisms. Yet trace fossils, such as fossilized footprints, give us direct evidence of organisms at a specific place in a specific time. The Laetoli footprints, for example, represent the earliest undoubted bipedal hominin, Australopithecus afarensis (Lucy’s species) at 3.6 million years ago. In December, a team led by Ellison McNutt from Ohio University announced that their reanalysis of some of the footprints from Site A at Laetoli were not left by a bear, as had been hypothesized, but by a bipedal hominin. Furthermore, because they are so different from the well-known footprints from Site G, they represent a different bipedal species walking within 1 kilometer (0.6 miles) of each other within the span of a few days! Recently uncovered and dated footprints in White Sands National Park, New Mexico, described in September by a team led by Matthew Bennett of Bournemouth University, place modern humans in the area between 23,000 to 21,000 years ago. Hypotheses as to how Indigenous Americans migrated into North America vary in terms of method (ice-free land corridor versus coastal route) as well as timing. Regardless of the means by which people traveled to North America, migration was highly unlikely, if not impossible, during the last glacial maximum (LGM), roughly 26,000 to 20,000 years ago. These footprints place modern humans south of the ice sheet during this period, meaning that they most likely migrated prior to the LGM. This significantly expands the duration of human occupation past the 13,000 years ago supported by Clovis culture and the roughly 20,000 years ago supported by other evidence. Furthermore, it means that humans and megafauna, like giant ground sloths and wooly mammoths, coexisted for longer than previously thought, potentially lending credit to the theory that their extinction was not caused by humans. Also interesting is that most of these footprints were likely made by children and teenagers, potentially pointing to division of labor within a community. Speaking of footprints left by ancient children, a team led by Eduardo Mayoral from Universidad de Huelva reported 87 Neanderthal footprints from the seaside site of Matalascañas in southwestern Spain in March. Dated at about 106,000 years ago, these are now the oldest Neanderthal footprints in Europe, and possibly in the world. The researchers conclude that of the 36 Neanderthals that left these footprints, 11 were children; the group may have been hunting for birds and small animals, fishing, searching for shellfish… or just frolicking on the seashore. Aw.

A version of this article was originally published on the PLOS SciComm blog.

Briana Pobiner | READ MORE

Briana Pobiner is a paleoanthropologist with the National Museum of Natural History’s Human Origins Program. She lead's the program's education and outreach efforts. 

Ryan McRae | READ MORE

Dr. Ryan McRae is a paleoanthropologist studying the hominin fossil record on a macroscopic scale. He currently works for the National Museum of Natural History’s Human Origins Program as a contractor focusing on research, education, and outreach, and is an adjunct assistant professor of anatomy at the George Washington University School of Medicine and Health Sciences.