Significant evidence of bipedalism was first found in the bipedal leg structure of early hominin Orrorin tugenensis who lived between 6 and 5.8 mya. Later in early hominin Ardipithecus, the position of the foramen magnum in their brain structure and spinal cord shows greater evidence of their reliance on bipedalism for greater locomotion. In an even later homin Australopithecus afarensis, features of the pelvis and legs provide even greater evidence of the full use of bipedalism for locomotion. A well developed arch in the foot of this hominin species found in Laetoli footprints, also suggest greater bipedal characteristics similar to hominids. The dental anatomy of early hominins greatly resembles the dental anatomy of the later hominid. For example, early hominin Ardipithecus who lived between 5.8 and 4.4 mya, shows to have had teeth similar in shape to the later hominid such as; larger canine teeth that resemble the structure of incisors seen in hominids. A later species of the Ardipithecus referred to as Ardipithecus ramidus, was found to have derived smaller teeth such as canines which are more similar to the dental anatomy of hominids. In later hominins such as Australopithecus afarensis who lived between 3.9 and 2.9 mya, evidence of a greater reduction in the size of molars and canines increased the similarity between the dental anatomy of hominins and hominids. Lastly, the facial traits of early hominin Sahelanthropus tchadensis who lived between 6 and 7 mya, show commonalities of the smaller hominid like facial traits such as large brow ridges and a flat face. These hominin traits help our understanding of modern human biology by informing us of the physical traits inherited by hominids by early ancestral hominins and how these traits evolved over time to become more similar to those of hominids.
The diversification of late hominins due to the pressures of selection and environmental adaptation, caused early hominins split into two diverse groups consisting of robust and gracile forms.Robust forms such as Paranthropus, developed specialized chewing abilities as their dental anatomy derived smaller front teeth and larger molars. Robust hominin traits resemble human traits on a much smaller scale than their counterpart, gracile forms. Gracile forms such as Australopithecus are thought to be direct ancestors of humans because they developed many features that resemble humans, more so than robust hominins. Gracile hominin Australopithecus garhi derived human like features such as a less robust head, similar arm to leg ratio and dentition characterized by large front teeth and premolars shaped more human like. A later gracile hominin Australopithecus sedbia, derived features further linking gracile forms to humans including the reorganization of the frontal lobe, pelvic shape and features of their hands and feet. The split of later hominids into these two forms affected the path that human evolution by introducing greater variation in traits that became more similar to humans, as they evolved in order to adapt to their changing environments. Human traits seem to be linked more closely to gracile forms of hominins as hominin diversification granted these hominins with greater human like traits.