I'm actually still confused as to why A is the right answer? I know it doesn't say that visual cues are exclusively responsible for the mechanism of kin recognition, but how are we to infer that they are not.
Is this answer trying to subtly go after the suggestion that inclusive fitness theory may be responsible for the "mechanism" as well? When I saw the word mechanism I was thinking of the actual physical process of
how they determine nonsiblings from siblings, and I wasn't necessarily thinking about
why they do it. So to me, it seemed perfectly acceptable that visual cues could explain how they recognize kin.
I'm confused...