If we look at that region in mammals that don't see so well, such as bats, and we find that bats that don't see so well have the purple type, we know that this is probably what's causing this disease.
如果我们研究那些视力不太好的哺乳动物的基因组， 比如蝙蝠， 我们发现蝙蝠视力不太好， 它们紫色类型的基因，我们知道这也许 是构成疾病的原因。