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Bipedalism Evolution

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Introduction One of the traits that distinguishes humans from other lineages is that humans are bipedal creatures. The human lineage acquired bipedalism many years ago, which led to a change in the morphology of the pelvis; this caused an alteration in the birthing mechanism compared to the last common ancestor. Childbirth is crucial to our existence because it determines the success of our lineage. Modern humans demonstrate a birth mechanism more complicated than other great apes. This is due to a large neonatal cranium, and body size, along with the rotation of the neonate (Grabowski 2012). The series of rotations is what distinguishes modern humans from great apes, lesser apes and monkeys (Weaver and Hublin 2009). Fetal rotation is necessary …show more content…

It is estimated that the hominins diverged from chimpanzees approximately 7 million years ago (Parente et al. 2011). The pelvis plays a role in walking upright and the delivery of a baby (Gruss and Schmitt 2015). In order to evolve bipedalism, several changes in pelvic morphology had to occur. There were two major morphological shifts that occurred during the evolution of bipedalism: reduction in the iliac height and relatively broad sacral alae (Machnicki et al. 2015). Bipedalism allowed modern humans to have iliac blades that are shorter and reoriented so they curve around the side of the body facing laterally and flaring outward (Gruss and Schmitt 2015). This morphology produced the bowl shape of the modern human pelvis. In comparison, non-primates have tall iliac blades, flat plates, and are oriented in the coronal plane which divides the body into dorsal and ventral parts. The lower pelvis morphology also changed in humans as compared to non-primates. In apes, the ischium is long whereas the ischium is shortened in humans. When humans walk upright, the body is supported by a single leg so the pelvis has a tendency to tip towards the unsupported side. In contrast, when apes walk bipedal, it is energetically costly, but they compensate by stretching out their arms and leaning their trunk towards the supported side. The gluteal muscles on the supported side are able to balance the trunk by pulling up the unsupported side of the pelvis. Clearly, the pelvic changes helped facilitate efficient bipedalism in modern

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