Final answer:
The first hominids are best characterized by bipedal locomotion and small brains. Features such as a brain size over 600 cc, tool-making capabilities, reduced jaw and teeth size, and anatomical structures adapted for upright walking are also distinctive of the genus Homo.
Step-by-step explanation:
The first hominids were characterized by bipedal locomotion and small brains. Early Homo species such as Homo habilis and Homo erectus demonstrated these characteristics. Homo habilis had a larger brain than earlier australopithecines and showed physical adaptations for making tools, including changes in bone structure and thumb positioning for better grip. Meanwhile, Homo erectus had traits like a broader pelvis, longer legs, and arched feet, which made them nearly as efficient at bipedal locomotion as modern humans, despite having larger jaws and teeth, a sloping forehead, and a relatively small brain compared to contemporary humans.Aside from bipedalism, the genus Homo is distinguished by various criteria such as a brain size over 600 cc, a round, globular skull, reduced size of jaws and teeth, and anatomical traits adapted for tool use. The presence of traits like a sagittal keel or humanlike feet with arches and ankles also characterizes early Homo species. However, the diversity of traits among hominin fossils makes the classification challenging and not always perfectly aligned with the criteria.