Footprints from the Past: The Mystery of the Midtarsal Break in Hominin Evolution

In 1978, an impressive discovery was unearthed from beneath the sands of the Olduvai Gorge in Tanzania which followed in the footsteps of some of humankind’s earliest ancestors, in the very most literal sense.

Anthropologist Mary Leakey had just announced the discovery of fossil footprints that had been preserved in volcanic ash for more than 3.5 million years at Laetoli, approximately 45 kilometers south of Olduvai Gorge, which gave an unprecedented glimpse at the foot morphology of some of the earliest bipeds to have traversed the sands of ancient Tanzania.

The discovery of the site had been made in 1976, although Leakey and her team would not conduct excavations for two more years. According to New Scientist, the prints were described as having been left by feet “shorter and wider than those of modern humans,” although the big toe “definitely points forward and is not splayed as in apes.”

The discovery remains one of the most significant in the archaeological study of human origins and our early ancestors. It also added to the lingering questions about when significant evolutionary developments began to occur that would differentiate early humans from our cousins among the great apes.

Specifically, questions have been raised about the flexion capacity of the modern human foot compared with that of early human ancestors. Extant varieties of non-human apes possess the ability to lift their heel independently from the rest of their foot on account of a midtarsal break, which humans do not possess. Thus, another question that arises from this has to do with when, precisely, early human ancestors lost this trait as they advanced toward bipedalism?

Answers to this question both vary and have also changed over time. For more than a decade, paleoanthropologist Jeremy DeSilva, an Associate Professor of Anthropology at Dartmouth College, has studied examples of early hominin feet like those uncovered at Olduvai Gorge, as well as the range of variation of flexibility in modern human feet, resulting in more questions about this ancient anthropological mystery than answers.

“Study of hominin metatarsals from Australopithecus afarensis, A. africanus, Homo erectus, and the metatarsals and a cuboid from the [Olduvai Hominid 8] foot show little capacity for dorsiflexion at the cuboid-metatarsal joint,” DeSilva observed in a 2010 paper which examined the midtarsal break phenomenon in depth. “These results suggest that hominins may have already evolved a stable midfoot region well adapted for the push-off phase of bipedalism by at least 3.2 million years ago.” In other words, early human ancestors would appear to have possessed feet that were generally more similar to humans than they are to extant varieties of great apes.

However, revisiting the question over the midtarsal break several years later, DeSilva discovered something truly fascinating: that vestiges of this ancient early anthropoid trait might still appear in some modern humans.

“The midtarsal break was once treated as a dichotomous, non-overlapping trait present in the foot of non-human primates and absent in humans,” DeSilva wrote in 2015. However, DeSilva found that further studies in recent years “indicates that there is considerable variation in human midfoot dorsiflexion, with some overlap with the ape foot.”

“These findings have called into question the uniqueness of the human lateral midfoot, and the use of osteological features in fossil hominins to characterize the midfoot of our extinct ancestors.”

Such findings may point to some rather unique implications. Jeffrey Meldrum, Ph.D., professor of physical anthropology at Idaho State University, is not only an expert on fossilized footprints left by early humans but also a proponent of the existence of a large, relict hominoid in North America commonly known as Sasquatch.

“A giant bipedal ape with relatively small brain, flat face, deep jaws, non-projecting canines, non-divergent hallux, flat flexible foot, as embodied by sasquatch was to be sure inconceivable to the anthropological community fifty years ago,” Meldrum wrote in 2017. However, unlikely though the proposition might seem to some, Meldrum has continued to pursue the possibility, carrying his studies of foot morphology among early human ancestors over into his evaluation of footprints purportedly left by Sasquatch, the results of which are quite telling.

“The action of the sasquatch foot itself, as it correlates with these distinctive footprints, is evident and observable in the Patterson-Gimlin film subject,” Meldrum wrote in a 2017 paper, referring to what is arguably the most famous instance of purported photographic evidence of the creature. However, it had not only been the footage of the creature that interested Meldrum, but also the footprints it left in the soft sand along Bluff Creek, castings of which were made by Patterson immediately after the film was obtained, and again days later by researcher Bob Titmus. Additionally, photos of the tracks were made by Lyle Laverty, a U.S. Forest Service employee, who visited the site shortly after news of the incident became publicized.

“Elevation of the heel, while flexed at the midfoot, disperses pressure beneath the entire forefoot, sparing relatively longer toes the bending stresses experience by human toes,” Meldrum explains, noting that under the right conditions, “this action may occasionally produce the distinctive pressure ridge evident in the Titmus cast,” adding that the same can be observed in other castings of purported Sasquatch footprints.

“The observable subtleties of correlated form and function within a distinct biomechanical context of this film and associated footprints render the cliché adage ‘Oh, that’s just a man in a fur suit’ quite vacuous, Meldrum concludes.

Indeed, if the presence of a midtarsal break were completely absent in the foot morphology of early human ancestors, as had once been suggested by DeSilva, this might complicate the idea that a large, unrecognized bipedal hominoid could still possess this apelike characteristic today. However, given the appearance of dynamics observed in certain humans living today that resemble a midtarsal break, it certainly warrants consideration that a creature like Sasquatch may possess such a trait.

As Meldrum notes of other cases where seemingly contradictory observations between modern humans and extinct human ancestors have been resolved, “It should be impressive that decades later these ‘inconceivable’ combinations of traits are now aligned with conventional wisdom, rather than at odds with it.” Indeed, further studies in the years to come may continue to reveal surprises about modern human anatomy and its evolutionary relationship to our ancestors.

And of course, the possibility also remains that such studies may also help us unravel clues about extant varieties of creatures that, in resembling some of those human ancestors now recognized as extinct, no modern scientist would have ever dreamed could have persisted into modern times.