But was an extra photopigment all that was needed to evolve trichromatic vision? 但是是否另一種感光色素必須完全進化成三色視覺?
In this view, trichromatic color vision can be considered a hobby of the preexisting spatial vision system. 或許也沒有這個必要,如果從這角度來看,我們可以把三色視覺看成既有空間視覺系統的次要活動。