Evolution of human colour vision other two human opsins. Middle Wavelength Sensitive Opsin (Green-sensitive opsin) – Encoded by the OPN1MW gene with a λmax of 530 found in the green region of the electromagnetic spectrum. Short Wavelength Sensitive Opsin (Blue opsin) – Encoded by the OPN1SW gene with a λmax of 430 found in the blue region of the electromagnetic spectrum. Certain parts of opsin genes and the vision of various species, including humans, has been known to change over time with different environmental changes. Recent studies have shown that primitive nocturnal mammalian ancestors had dichromatic vision consisting of UV–sensitive and red–sensitive traits. A change
Squirrel monkey in the mid-teens. Colour vision in squirrel monkeys has been extensively studied as a stand-in for human ailments. In humans, two genes for colour vision are found on the X chromosome. Typically, one gene (OPN1LW) produces a pigment that is most sensitive to the 564 nm wavelength, while the other gene (OPN1MW) produces a pigment most sensitive to 534 nm. In squirrel monkeys, there is only one gene on the X chromosome but it exists in three varieties: one is most sensitive to 538 nm, one to 551 nm, and one to 561 nm. Since males have only one X