We’d like to congratulate paleoanthropologist Dr. Jason Lewis and his colleagues on two exciting publications reporting on a 4.3 million-year-old hominid specimen and a Neanderthal found in France near the time of the Neanderthals’ disappearance. Their findings propose significant updates to our understanding of our earliest human ancestors, as detailed below.
A Reconfigured Timeline and Family Tree for Australopithecus anamensis
Dr. Lewis is listed as first author on “A 4.3-million-year-old Australopithecus anamensis mandible from Ileret, East Turkana, Kenya, and its paleoenvironmental context,” published in the Journal of Human Evolution. This publication concerns a hominin mandible known as KNM-ER 63000 and associated vertebrate remains recovered in 2011 from Area 40 in East Turkana, Kenya. Tephrostratigraphic and magnetostratigraphic analyses conducted by Dr. Lewis and his colleagues suggest these fossils date to approximately 4.3 Ma (million years ago), and KNM-ER 63000’s anatomy indicates attribution to Australopithecus anamensis, the earliest candidate to be commonly considered a direct ancestor to Homo sapiens due to its more humanlike anatomy compared to other species existing around the same span of time.
KNM-ER 63000’s greatest significance lies in how its age impacts our prior understanding of Au. anamensis’ length of existence and its ancestors. With its age pointing to about 4.3 Ma, KNM-ER 63000 is the oldest known specimen of Au. anamensis, predating existing samples by around 100,000 years or more. As a result, the known timeline for Au. anamensis’ existence is now extended such that it overlaps with Ardipithecus ramidus fossils from Gona, Ethiopia. Ar. ramidus has been an ancestral candidate for Au. anamensis, but possesses morphological traits more apelike than mainstream scientific thought theorizes Au. anamensis’ ancestor to be. Dr. Lewis and his colleagues’ finding that KNM-ER 63000 and other Au. anamensis existed concurrently with Ar. ramidus, rather than after the disappearance of Ar. ramidus as previously supposed, strongly suggests that Ar. ramidus was not ultimately Australopithecus’ (including Au. anamensis and KNM-ER 63000’s) ancestor, but rather its relative, implying a broader family tree than previously believed for this period more than four million years ago.
Proposed Significance of Internal Factors in the Disappearance of the Neanderthals
Dr. Lewis is also the co-author of a second paper titled “Long genetic and social isolation in Neanderthals before their extinction,” published recently in Cell Genomics. This publication reports the 2015 discovery of a late Neanderthal individual from Grotte Mandrin in Mediterranean France, nicknamed Thorin, who likely belonged to one of the last representative Neanderthal populations in this region of France and is the most complete Neanderthal individual found in France since 1979. Thorin is still under excavation, with recovered fragments including part of a mandible and 31 teeth, including two supernumerary fourth molars—an extremely rare phenomenon in modern humans described in only a few instances previously for Neanderthal and Paleolithic modern humans.
Bottom: Virtual reconstruction of the jaw and dental elements of Thorin in tilted (upper left), anterior (upper right), and lateral (bottom right and left) views.
Combining archaeological, chronostratigraphic, isotopic, and genomic analyses, Dr. Lewis and his colleagues show Thorin’s group was isolated for 50 ka (thousand years) from other known late European Neanderthals of differing lineages with no evidence of introgression (interbreeding), despite living in relative proximity to them. Genetic isolation also appears in other instances of known Neanderthals, suggesting a trend of small group sizes and least two or three distinct Neanderthal lineages in Europe during the late Neanderthal period. Thorin’s existence and genetic isolation close to Neanderthals’ disappearance around forty thousand years ago carries significant implications for potentially resolving competing hypotheses about the causes of Neanderthals’ disappearance.
Genetic analysis of other late Neanderthals indicates they belonged to a single metapopulation with no significant evidence of population structure among them. Thorin contributes the first direct genomic evidence of such structure among late European Neanderthals; Dr. Lewis and his colleagues’ analysis indicates Thorin belongs to a lineage diverging 100-105 thousand years ago from the ancestral European Neanderthal lineage and therefore represents a remnant of earlier European Neanderthals, specifically from eastern Europe. Thorin’s genomic analysis also shows increased homozygosity compared with other late Neanderthals, another indicator of genetic isolation. Available data also suggests that the Gibraltar Neanderthals, which Thorin and his peers share a genetic branch with, might have been members of an extended southwest European metapopulation, and raises the possibility of a much later dating for those individuals than previously anticipated.
Bottom: Distribution through time and space of distinct early to late Neanderthal groups, including Thorin.
The 50,000-year-long genetic isolation of the Thorin lineage raises new questions about the causes of the Neanderthals’ extinction and the nature of interactions between Neanderthals and the earliest Homo sapiens arriving in Europe. The Thorin lineage’s genetic isolationism relatively close to the disappearance of Neanderthals suggests social and ethological organization may have played a greater part in Neanderthal extinction than previously assumed, especially when considering divergences among long-isolated Neanderthal groups facing H. sapiens populations understood to have possessed larger and more complex social networks.
These two papers present intriguing data and suggestions radically changing our collective understanding of our early human ancestors. We’re highly honored to count Dr. Lewis as a part of our team and one of our many published scholars pursuing exciting work enhancing our understanding of our collective past.
Access the free version of the paper on Thorin’s discovery and genomic analysis here.