Evo-Ed: Integrative Cases in Evolution Education

Cases for Evolution Education

Monkey Opsins

Humans have trichromatic vision. Our eyes detect colors in the visible range of the spectrum using three different cone cell types, each maximally stimulated by a different wavelength of light. Some humans are colorblind, meaning that their eyes detect colors in a more limited region of the spectrum using only one or two different types of cone cell.

Color vision capabilities in the world’s two major groups of monkey species are patterned in the same way. Generally, monkey species from Africa, Europe and Asia (the old world monkeys) have trichromatic vision, whereas monkey found in South and Central America (the new world monkeys) have dichromatic vision.

This case will examine the evolution of trichromatic vision in old world monkeys.

Image of a Mandrill represented with three colors and two colors; simulating what a tricromate and a dichromate would see.
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Trichromatic monkeys seem to have a superior ability when foraging by color discrimination, but dichromatic monkeys may be superior when foraging using shape discrimination.

Cell Biology

Cone cells send a signal to the brain when retinal molecules bound to opsin proteins are stimulated by photons of particular wavelengths.

Molecular Genetics

The genes encoding opsin proteins are very closely related. Research indicates that an ancestral opsin gene duplicated in old world monkeys, and subsequent mutations in the new copy resulted in two types of opsin, instead of just one.


Why do all the trichromatic monkeys live in the Old World, while all the dichromatic monkeys live in the New World? An analysis of the genetic relatedness among monkey species can give us clues about when and where color vision evolution occurred.