Final answer:
The earliest hominins looked ape-like because they were evolving from a common ancestor shared with great apes and retained many ape-like features suited to their environments. As they adapted to new ecological niches, they developed a mix of ape-like and human-like traits. This evolution included changes conducive to bipedalism while maintaining some arboreal adaptations.
Step-by-step explanation:
The earliest hominins would have looked very ape-like because they evolved from a common ancestor shared with the great apes. The evolutionary lineage that led to modern humans took millions of years, with our ancestors gradually acquiring traits that distinguished them from their primate relatives. Initially, these early hominins retained many physical characteristics typical of apes, such as longer arms and smaller brains when compared to modern humans.
For example, Australopithecus afarensis, an ancient hominin species that lived between 3.9 and 2.9 million years ago, had a mix of ape-like features and characteristics that were similar to humans. They had long arms and curved finger and toe bones, features associated with living in trees. Yet, aspects such as a broader pelvis suggested adaptations to bipedal locomotion, indicating a transition towards walking upright like humans.
Over time, species like Homo habilis and Homo erectus developed more human-like qualities, including larger brains and smaller teeth. Changes in pelvis shape and limb proportions facilitated improved bipedalism. Despite these advances, early Homo species still had differences from modern humans, such as a sloping forehead and larger jaws and teeth.
The appearance of the earliest hominins was largely due to their place in the evolutionary timeline. They were adapting to new environments and survival challenges, which led to a mix of ape-like and human-like traits. These adaptations included bipedalism, which likely provided an advantage for tasks such as foraging for food and monitoring predators over the tall grasses of the African savannah. However, the retention of certain ape-like features suggests that they still occupied environments where these traits were beneficial, such as forests where climbing was necessary.
Significant fossil discoveries, including the Laetoli footprints and various skeletal remains, have provided evidence of the adaptations of bipedalism in early hominins. Furthermore, hominin species like Homo naledi also exhibited a mosaic of ancient and modern traits, indicating a gradual evolution towards the human form.