Primates and eyes vision

Did you know how primates trichromatic eyes vision evolve? After has several reading, for me the pathway of the evolution is very beautiful. To understand it, is not rocket science, just a basic knowledge about genetic.

The informations from readings catch my attention  to write this post because  they give the good example of how the mutation via gene duplication give the benefit to primates and also the evolution of the old world primates and new world primates is differ and also they give good explanation about X-inactivation in female.

First, I would like to summarize 2 different pathway of evolution in primates colour vision. Before I explain more detail, just for your information mammals have 2 type of eyes vision dichromatic and trichromatic. The figures below show that the different between dichromatic and.trichromatic:

In human is trichromatic eyes vision which have 3 pigment M,L and S. M and L pigment genes  next to each other on the chromosome X and S pigment on the chromosome 7. Human and Old World primates shares a common pathway of the evolution of eyes colour vision.


Humans and other Old World primates carry both M- and L-pigment genes on each of their X chromosomes and have trichromatic vision. But in testing the color vision of New World primates over the past several decades, one of us (Jacobs) discovered that trichromacy occurs only in a subset of females. All of the New World males and roughly a third of the New World females examined showed the lack of sensitivity to colour differences in the middle-to-long wavelengths that is typical of dichromats. Trichromacy was not universal among primates after all.

How to explain the phenomena above? I just want to give keys in understanding the phenomena. In explaining the evolution from dichromatic to trichromatic it involve several mutation. In the case of New world primate, the explanation is about the X-inactivation and the role of randomness.

Lets go deeper in how the evolution of dichromatic to trichromatic. In common ancestors of both Old World and New World primates the ancestral X-linked of longer-wave-length pigment underwent the successive mutation which are produce the 3  longer-wave-length pigment in the gene pool.


After the Old World and New World primate lineages became isolated from each other (geographical isolation),an error in recombination in the Old World Primates, which is the gene duplication occur and produce 2 pigment of eyes vision at the X-chromosome. This phenomena explain why M-pigment gene and L-pigment gene on human X-chromosome are almost identical.

The different story if we look at New World primates, they did not have the gene duplication and all the male are dichromatic and some female are trichromatic. Why some female are trichromatic?. X-inactivation will explain this phenomena. Female has 2 X-chromosome so need to inactivate to balanced the expression of XY males. The role of randomness of X-inactivation in retina make some New World primates female has trichromatic eyes vision.

Based  on the role of randomness in X-inactivation in retina, the female of the Old World primate has potential to have 4 types of eyes vision pigment. This phenomena called super colour vision.

Reference- Mostly based on article in Sciencetific American April 2009- "the evolution of primates eyes vision"