Final answer:
Non-human apes are poorly adapted for walking upright due to their evolutionary history and the advantages of their arboreal lifestyle.
Step-by-step explanation:
The reason why non-human apes are poorly adapted for walking upright is a result of their evolutionary history and ecological niche. Primates evolved from tree-dwelling ancestors, which favored adaptations for climbing and brachiation. While bipedalism offered advantages for our human ancestors, such as freeing up their hands for tool use and enabling long-distance travel, other apes were better suited for their arboreal lifestyle. Their anatomy, including long arms, rotating shoulder joints, and feet adapted for gripping branches, allowed them to navigate trees more efficiently, which was advantageous for their survival.