Justin Bieber is Part-Lemur
Mantis shrimps are not the only community to claim genetic ties to Bieber; lemurs also believe that Justin is related to them. Since lemurs are nocturnal, sunshine can really scare the living daylights out of them (pun definitely intended). Perhaps it is not that Justin's eyes are too receptive to light, but that they are not receptive enough, causing him to squint even when it is not a particularly bright day. Fun fact: lemurs also believe that Fiona Apple is one of them, a claim that can be confirmed on sight.