This week, an international team of researchers unveiled an analysis of a fossil unearthed in Bulgaria, a finding that could dramatically reshape the established timeline for the emergence of early human ancestors. This fossil, a 7.2-million-year-old femur belonging to a specimen of Graecopithecus, suggests, based on the bone’s morphology, that this hominin was already walking upright on two legs by that period. This pushes the earliest known fossil evidence of this characteristic back in Africa by more than a million years.
The fossil, discovered at the Azmaka site near the Bulgarian city of Chirpan on the Upper Thracian Plain, underwent intense scrutiny as part of an international collaboration involving the National Museum of Natural History in Bulgaria, Aristotle University of Thessaloniki (Greece), the Senckenberg Center for Human Evolution and Paleoecology at the University of Tübingen (Germany), and the University of Toronto (Canada).
The complete study detailing this find is featured in the journal Palaeodiversity and Palaeoenvironments, describing characteristics that tie this specimen to the evolutionary lineage leading to modern humans.
Until now, the scientific consensus held that bipedalism—considered a fundamental milestone in human evolution and one of our most defining traits—developed in Africa around six million years ago. However, the Azmaka femur exhibits several morphological features that experts believe can only be accounted for if its owner moved using two legs.
Professor David Begun from the University of Toronto, one of the study’s lead authors, asserted that this ancestor, which we classify under the genus Graecopithecus, dating back 7.2 million years, might be the most ancient human ancestor known.
The first Graecopithecus specimen identified was a segment of the lower jaw, found at a site close to Athens. In 2017, this same research group analyzed these fossil remains and concluded, based on the morphology of the tooth roots, that Graecopithecus should indeed be considered an early human ancestor.
Nevertheless, that jawbone could not provide insights into the creature’s mode of locomotion. The discovery of the femur in Bulgaria has filled this gap, offering crucial data on how this primitive hominin moved.
It is likely that the individual possessing the femur was a female weighing approximately 24 kilograms, living near a river in a savanna environment very similar to those found in East Africa today. Professor Nikolay Spassov from the National Museum of Natural History in Bulgaria elaborated on the features supporting the bipedalism hypothesis: a series of external and internal morphological traits, such as an elongated and upward-oriented neck connecting the shaft to the head, specialized attachment sites for the gluteal muscles, and the thickness of the outer bone layer, all show similarities to the femurs of fossil bipedal human ancestors and those of modern humans. It is precisely in these aspects that the Bulgarian fossil diverges from the femurs of arboreal apes.
However, the researchers caution that the walking mechanics of Graecopithecus were not identical to ours. Spassov clarified that Graecopithecus did not move exactly like contemporary humans. The Azmaka femur, in effect, blends features typical of African apes with others observed in later bipedal creatures, suggesting we are observing a transitional form.
For Begun, Graecopithecus represents a stage in human evolution positioned between our tree-dwelling ancestors and those that walked the ground, such as Danuvius guggenmosi (nearly twelve million years old, found at the Hammershmiede site in southern Germany), as well as later finds from East Africa. According to the researcher, it can certainly be called a missing link.
The origin of this ancestor appears to also have European roots. Scientists posit that Graecopithecus likely descended from Balkan-Anatolian apes living eight or nine million years ago, such as Ouranopithecus and Anadoluvius, which themselves originated from ancestors inhabiting Western and Central Europe. This genealogy suggests that the European continent may have played a significantly more substantial role in the very earliest phases of human evolution than previously assumed.
Inevitably, the question arises: how and why did these ancestors eventually end up in Africa? The answer, according to the study’s authors, may lie in profound climatic shifts affecting the Eastern Mediterranean and Western Asia during the Late Miocene. Professor Madelaine Böhme from the Senckenberg Center for Human Evolution and Paleoecology at the University of Tübingen explained that we know large-scale climatic changes in the Eastern Mediterranean and Western Asia led to the periodic emergence of vast semi-deserts and deserts between eight and six million years ago. This phenomenon, Böhme noted, triggered several dispersal waves of Eurasian mammals into Africa, laying the groundwork for the modern fauna of African savannas.
The study’s authors consequently propose that hominoids also migrated southward along these routes. At this juncture, it remains unclear whether speciation separating the ancestors of chimpanzees, gorillas, and humans had already occurred in Europe and whether these dispersal waves were the decisive factor in the genetic isolation of their respective lineages. It seems plausible that Graecopithecus or closely related forms dispersed from the Balkans into Africa, where, starting around six million years ago, other early human ancestors like the genus Orrorin appeared, followed later by Australopithecus afarensis, whose most famous representative is the fossil known as Lucy.
This discovery introduces a novel scenario for the origin of bipedalism and positions the Balkans as a pivotal region for understanding human evolution. Research and excavations are ongoing at Azmaka and other locations in the region, aiming to uncover further Graecopithecus specimens, which will allow researchers to expand their knowledge of the ecology and evolution of this remarkable primitive upright creature and its contentious place in our family tree.
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