Why this is right
This rule would help us conclude that "there is probably a similarity between causes", and our actual conclusion is "it is likely that cave dwellers engaged in similar activities", so we should consider whether we can make this work. The premise talked about a similarity of skeletal fractures. The conclusion is talking about a similarity of activities (chasing and tackling animals). Can we call "chasing and tackling animals" the cause, and "skeletal fractures'" the effect? Sure. It's not explicitly said, but that's the common sense interpretation of what this author is suggesting. The whole reason the author surmises that early hominids were also chasing and tackling animals is because she's trying to explain the curious fact of why these early hominids had skeletal fractures like rodeo riders do. Essentially, the author is thinking, "If these hominids have skeletal fractures that match what rodeo riders have, then they both got these fractures from the same activity."
Skill tested: Principle-Strengthen · how this choice captures the argument's function is the move to repeat next time.