Final answer:
The earliest hominin looked ape-like due to their evolutionary history, sharing a common ancestor with great apes and retaining many physical characteristics best suited for arboreal life. However, they also developed bipedal adaptations, signifying a transitional stage towards modern human traits.
Step-by-step explanation:
The reason the earliest hominin, such as Australopithecus afarensis, looked very ape-like is due to their evolutionary heritage. These early ancestors shared a common ancestor with that of the great apes. Australopithecus, like apes, had many physical characteristics suited for life in the trees, such as long arms and long, curved fingers and toes. However, they also exhibited bipedalism indicative of transitional adaptations towards a more human-like stature. The pelvis of Australopithecus, for example, began to resemble that of modern humans, suggesting a bipedal mode of locomotion. Over time, successive hominin species like Homo habilis and Homo erectus continued to evolve human-like traits, including increased brain size and reduced jaw and tooth size, while maintaining some ape-like characteristics such as long arms. The evolutionary process reflects a complex interplay between adaptation to a changing environment, including bipedalism, and the retention of arboreal adaptations from their ape-like ancestors.