Final answer:
A trend in hominin evolution since the australopithecines is the increase in brain size and complexity, enhanced bipedalism, and the reduction in sexual dimorphism.
Step-by-step explanation:
A significant trend in hominin evolution since the australopithecines is the increase in brain size and complexity. Early hominins like Australopithecus had smaller brains relative to body mass when compared to modern humans. As we follow the evolutionary line, we see descendants such as Homo erectus who had brains three-fourths the size of modern humans. This species also developed more advanced stone tool-making skills than their australopithecine predecessors.
Another trend is the evolving bipedalism that became more pronounced over time. The Australopithecus species were bipedal, but their anatomy suggests they also spent time in trees. In comparison, Homo erectus was fully adapted to walking upright, which is evidenced by changes in the pelvis and lower limb structure that support long-distance walking on two feet.
Additionally, there is a trend towards reduced sexual dimorphism in the hominin lineage. Early species like Australopithecus showed greater size differences between males and females, akin to great apes. Over time, this dimorphism diminished, as seen in later hominins and modern humans, where males are on average only around 15-20% larger than females.