A 7.2-million-year-old thigh bone discovered in Bulgaria is challenging conventional wisdom about the origins of human walking. The fossil, attributed to the species Graecopithecus, displays a mix of traits suggesting it was capable of both four-legged movement and some form of upright walking – a key step in human evolution. This discovery raises the possibility that bipedalism may have emerged outside Africa, rather than solely within it, before spreading.
The Graecopithecus Enigma
Graecopithecus is a controversial fossil ape from the Late Miocene epoch. Previously known only from fragmented jaw and tooth remains, the new thigh bone provides the most complete skeletal evidence yet for this species. Researchers led by Professor Madelaine Böhme from the University of Tübingen analyzed the bone, finding features like an elongated femoral neck and distinct muscle attachment points that resemble those of early human ancestors.
However, it wasn’t a fully committed biped. The bone structure suggests a transitional form: not a specialized tree-climber like orangutans, but also not walking upright as efficiently as modern humans. The estimated body mass of this individual (around 23–24 kg, similar to a small chimpanzee) further indicates a creature in the early stages of adapting to terrestrial movement.
Why This Matters: Rethinking Human Origins
The traditional narrative of human evolution places Africa as the primary cradle of bipedalism. Yet, this discovery suggests that early forms of upright walking may have evolved in Europe, specifically in the Balkan region, and later spread into Africa. The Azmaka site where the fossil was found was a bush and forest savanna environment – a landscape of seasonal rivers and open woodlands – which may have favored early experimentation with walking on two legs.
Professor David Begun of the University of Toronto notes that Graecopithecus fills a gap between older European apes like Danuvius guggenmosi and later African hominins. The team hypothesizes that climatic shifts in the eastern Mediterranean forced Eurasian mammals, including potential Graecopithecus descendants, to disperse into Africa, possibly contributing to the ancestry of later hominins.
Future Implications
The Azmaka femur provides a rare glimpse into how upright walking first took hold in a landscape millions of years before the earliest widely accepted human ancestors appeared in Africa. Whether this discovery reshapes our understanding of human origins will depend on future fossil finds. But for now, it adds crucial evidence to the ongoing debate about where and how bipedalism, one of the defining traits of humanity, first emerged.
This research, published in Palaeobiodiversity and Palaeoenvironments in November 2025, emphasizes that the story of human evolution may be more complex and geographically diverse than previously believed.
