Researchers from King’s College London have made a fascinating discovery about the evolution of a tiny bone in the human knee, shedding light on the remarkable journey of our ancestors towards upright walking.
The Enigmatic Fabella
The research investigates the lateral fabella, a tiny bone resembling a sesame seed located in the back of the knee joint. In most primates, this bone is present,a but it is often absent in hominoids, the group that includes humans and our closest relatives.
This discovery is particularly interesting because even amongst the hominoid group, humans have an unique variant of the fabella. In contrast to other primates, where the fabellae appear as both medial and lateral pairs, humans often have only a lateral fabella. A discovery of this bizarre evolutionary road could open doors to understanding how our distant ancestors managed to finally edge into bipedal locomotion from walking on all fours.
Solivagant (Unpacking the Evolutionary Enigma)
Statistical modeling was applied by the team to extrapolate the presence of three sesamoid bones in the knee: cyamella and medial fabella, lateral fabella. And they found something intriguing: primates with fabellae were 50 times more likely to have ancestors that also had them.
This all—but explains why the evolution of these knee bones has been so connected with the general workings-out of the hominoid lineage. They also discovered that most other primates display the medial and lateral fabellae together, lacking solely in humans. In humans, this ‘decoupling’ of the fabellae could even be a form of ‘exaptation’, when an existing body structure changes its function for new use – in this case to help perform bipedal gait.
More research is necessary to confirm this hypothesis with regard to the biomechanics of the fabella, but results thus far are compelling. Insights into the remarkable journey taken by our upright-walking human ancestors may come from new University of Queensland research on a 400,000-year-old thigh bone.
Conclusion
When the lateral fabellum evolved in primates, this led to some interesting insights into how humans learnt to walk on their two feet. The unusual course that this little bone took in our own lineage may provide a useful key to the major evolutionary changes responsible for the transition of our ancestors from four-legged animals to walking on two legs. Further studies of the biomechanics and function of this mysterious structure could provide further clues as to the fascinating narrative through which human beings evolved.
