Final answer:
Ardipithecus ramidus is classified as a hominin due to its anterior foramen magnum indicating bipedalism, small upper arm bones, and reduced canines, suggesting less need for aggression and a shift in social behavior.
Step-by-step explanation:
Ardipithecus ramidus has been classified as a hominin because it exhibited traits indicative of bipedalism. One of the most significant traits is the anterior position of the foramen magnum, which suggests that Ardipithecus walked upright. Additionally, the species had other features such as small upper arm bones and a reduced canine size, unlike the larger canines of African ape males. These characteristics, along with archaeological findings suggesting a combination of terrestrial bipedalism and arboreal quadrupedalism, align Ardipithecus ramidus with hominin lineage. The reduced canines correlate with a shift in social behavior, diminishing the need for aggression and indicating a possible preference for less aggressive males during selection processes.