Final answer:
To distinguish early hominins from other apes, features such as bipedalism, increased brain size, changes in thumb position and grip for tool-making, pelvic morphology, and dental anatomy are examined.
Step-by-step explanation:
The process to distinguish the earliest hominins from other apes is primarily based on skeletal morphologies and archaeological evidence. One major distinguishing feature is bipedalism, reflecting an upright posture and walking on two legs, which is seen in species like Australopithecus and early members of the genus Homo. However, bipedalism is not the sole criteria for classification under the genus Homo.
Other criteria include brain size, pelvic morphology, dexterity for tool-making, and dental anatomy. For instance, Homo habilis showed an increase in brain size to around 600-750 cc, a repositioning of the thumb allowing for a better grip and dexterity needed for tool creation, and a less prognathic (projecting) jaw compared to earlier hominins such as Australopithecus.
Additionally, the shape of the pelvis in hominins like Australopithecus afarensis became wider and shorter, aligning more with human-like bipedal locomotion. Early Homo species, such as Homo erectus, exhibited longer legs and arched feet relative to quadrupedal primates, showing an efficient bipedal locomotion. Yet, they retained traits like a sloping forehead and larger jaws distinct from modern Homo sapiens.