Bowmaker J K
Department of Visual Science, University College London, UK.
Eye (Lond). 1998;12 ( Pt 3b):541-7. doi: 10.1038/eye.1998.143.
The expression of five major families of visual pigments occurred early in vertebrae evolution, probably about 350-400 million years ago, before the separation of the major vertebrate classes. Phylogenetic analysis of opsin gene sequences suggests that the ancestral pigments were cone pigments, with rod pigments evolving last. Modern teleosts, reptiles and birds have genera that possess rods and four spectral classes of cone each representing one of the five visual pigment families. The complement of four spectrally distinct cone classes endows these species with the potential for tetrachromatic colour vision. In contrast, probably because of their nocturnal ancestry, mammals have rod-dominated retinas with colour vision reduced to a basic dichromatic system subserved by only two spectral classes of cone. It is only within primates, about 35 millions years ago, that mammals 're-evolved' a higher level of colour vision: trichromacy. This was achieved by a gene duplication within the longer-wave cone class to produce two spectrally distinct members of the same visual pigment family which, in conjunction with a short-wavelength pigment, provide the three spectral classes of cone necessary to subserve trichromacy.
五大类视觉色素的表达在脊椎动物进化早期就已出现，大概在3.5亿至4亿年前，即在主要脊椎动物类别分化之前。视蛋白基因序列的系统发育分析表明，原始色素是视锥色素，视杆色素是最后进化出来的。现代硬骨鱼、爬行动物和鸟类的一些属同时拥有视杆和四种光谱类型的视锥，每种视锥代表五大视觉色素家族之一。四种光谱不同的视锥类型的组合使这些物种具备了四色视觉的潜力。相比之下，可能由于其夜行性的祖先，哺乳动物的视网膜以视杆为主，其色觉退化为仅由两种光谱类型的视锥所支持的基本双色系统。直到大约3500万年前的灵长类动物中，哺乳动物才“重新进化”出了更高水平的色觉：三色视觉。这是通过长波视锥类中的一个基因复制实现的，产生了同一视觉色素家族中两个光谱不同的成员，它们与一个短波色素一起，提供了支持三色视觉所需的三种光谱类型的视锥。
