Absolute thresholds seem to differ across species. for example, humans are much better at detecting visual stimuli than moles. however, dogs have a much better sense of smell than humans. why do you think that humans evolved to favor vision over the other 4 senses?

Well, I'd say because of bipedalism (standing and walking up-right).

Explanation:

Favoring vision among our other four senses is seen as a consequence of how human evolution has developed so far. Thanks to bipedalism we could free our hands from the ground, then, we started using tools better; we gained a way of saving energy when commuting for long distances; and we allowed our selves to have a wider field of vision, which helped us in many ways, but especially in preventing attacks from predators.

This last evolutionary feature is what originated our nowadays-very-accute vision.

b) the planets year length would be longer

hope this !