The ability to see color is something that many people take for granted. But, there are many people who go about life thinking that their vision is “normal,” when they are really experiencing their sense of sight through a color vision deficiency.
A typical person relies on the color of fruit to determine its ripeness. Looking at a green banana signals to the brain that it is not ripe nor is it ready to be eaten; while looking at a brown banana signals that it is overripe and should be thrown away or used for baking purposes. What if you could not see the color and had to rely on the commonly overlooked details, like shape or texture to identify the fruit?
Humans are not the only ones who can have color vision deficiencies as it is typical in a variety of animal species. Primate color vision has sparked interest of researchers because it is highly variable (Osorio, Smith, Vorobyev, & Buchanan-Smith, 2004). Dichromatic vision is the norm for many mammals, not including humans. As for primates, New World monkeys show a polymorphism of color vision as some are dichromatic, while others are trichromatic (Saito et al. 2003). Old world monkeys and the howler monkey, a New World monkey, are trichromats. This is due to a gene duplication different from that of Old World monkeys (Osorio et al.).
Brief History of primates and color vision:
Records state that the first primates appeared at 80-90 Ma (Jacobs, 2009). It is believed that the primates living at the time were nocturnal. Similar to other eutherian mammals (a mammal that is indigenous to North America, Europe, Africa, and Asia), primates had dichromatic color vision where their retinas most likely “featured single representative pigments from the SWS1 (short-wavelength-sensitive) and LWS (long-wavelength-sensitive) gene families” (Jacobs).
As time progressed, primate lineages became more active in the daylight compared to the nocturnal life of previous primates. Jacobs states that this “set the stage for alterations in photopigments and color vision.”
He continues to explain that the M and L photopigments were derived from duplication of the original X-chromosome opsin gene. Because the three-pigment arrangement of trichromatic color vision is not typically shared with members of other anthropoid groups like the New World monkeys, the X-chromosome opsion gene duplication is thought to have occurred around 30-40 Ma at the base of catarrhine, or Old World monkey, radiation.
New World Monkeys
According to Jacobs, three or more types of cone pigments are typical among vertebrates. In eutherian mammals, primates are the sole species with three cone pigments. A more varied opsin gene/color vision arrangement is present in New World monkeys. Most of these monkeys have a total of six unique photopigment phenotypes. A male or female homozygous New World monkey can express one of three LWS opsin genes with the SWS gene, which is common in this species, then...