The evolution of the upright posture and gait—a review and a new synthesis

Abstract

During the last century, approximately 30 hypotheses have been constructed to explain the evolution of the human upright posture and locomotion. The most important and recent ones are discussed here. Meanwhile, it has been established that all main hypotheses published until the last decade of the past century are outdated, at least with respect to some of their main ideas: Firstly, they were focused on only one cause for the evolution of bipedality, whereas the evolutionary process was much more complex. Secondly, they were all placed into a savannah scenario. During the 1990s, the fossil record allowed the reconstruction of emerging bipedalism more precisely in a forested habitat (e.g., as reported by Clarke and Tobias (Science 269:521–524, 1995) and WoldeGabriel et al. (Nature 412:175–178, 2001)). Moreover, the fossil remains revealed increasing evidence that this part of human evolution took place in a more humid environment than previously assumed. The Amphibian Generalist Theory, presented first in the year 2000, suggests that bipedalism began in a wooded habitat. The forests were not far from a shore, where our early ancestor, along with its arboreal habits, walked and waded in shallow water finding rich food with little investment. In contrast to all other theories, wading behaviour not only triggers an upright posture, but also forces the individual to maintain this position and to walk bipedally. So far, this is the only scenario suitable to overcome the considerable anatomical and functional threshold from quadrupedalism to bipedalism. This is consistent with paleoanthropological findings and with functional anatomy as well as with energetic calculations, and not least, with evolutionary psychology. The new synthesis presented here is able to harmonise many of the hitherto competing theories.

Significance of adequate postural control in the appearance of habitual upright bipedal locomotion

“…Brachiation, therefore, cannot be the origin of human bipedalism. Similarly, the aquatic ape theory [71] proposes that water supports the body and facilitates the maintenance of an upright bipedal posture in apes. However, once the apes are out of the water, they must rely on the nervous system to control their posture.…”

Bipedalism in non-human primates: a comparative review of behavioural and experimental explorations on catarrhines

“…Bipedalism has also been correlated with specific ecological contexts such as moving on flexible branches [11,23] and in waterlogged environments (flooded forests, swamps, etc) (for a review see Table 1 in [24]). Finally, when the environment is set up experimentally, the frequency of bipedal behaviour increases significantly [25].…”

Evolution of the Early Solar System in Terms of Big History and Universal Evolution

“…For example, there is a wellgrounded hypothesis on the role of the cooling that took place 6-8 million years ago and led to the formation of large open spaces in the East Africa. It promoted the evolution of Hominids named Dryopithecus living in trees into bipedal upright walking Hominids of the Australopithecus or another type (Kessler 2017;Niemitz 2010).…”