But was an extra photopigment all that was needed to evolve trichromatic vision? 但是是否另一种感光色素必须完全进化成三色视觉？
In this view, trichromatic color vision can be considered a hobby of the preexisting spatial vision system. 或许也没有这个必要，如果从这角度来看，我们可以把三色视觉看成既有空间视觉系统的次要活动。
