The ability to see colours is a unique and crucial mutation that only some species have. Species have a wide range of colour that are seen and many of these species can not see colour at all. Over time, some species including primates and later on humans, developed the ability to see colours and became trichromatic. There are types of monkeys that are dichromats and some that are trichromats. The are multiple theories about why this change occurred and why it happened to only some types of species. Trichromatic vision is the ability to see three spectrums of colour. It is achieved through cone cells that peak in violet, yellow and green spectrums. The violet wave is a short wave (S), the yellow wave is a long wave (L), and the green wave is a medium one (M). The sensitivity of these cones is deterimened by Opsin. Opsin is a primary pigment found in a primate’s eye, the sequence of the opsin protein helps to contribute to a colour sensitivity. Dichromats are species that only have two functioning colour receptors or cones in their eyes. A dichromat can only distinguish between blue and greens, they don’t have the cone to see reds. There are also species like a nocturnal owl monkey, that have monochromatic vision. They are only able to see black, white and greys. Monochromats are very rare in primates, since most primates are either trichromats or dichromats. Every pirmate has a S ospin on their seventh chromosome. Trichormatics also have two Opsin genes that are found on the X chromosome. These two genes are adjacent to each other and code for M and L pigments. The problem is that new world monkeys only have a single gene on their X chromosome. This gene codes for either M or L. This causes for every new world male monkey to be dichromatic since they can only get the M or the L photopigment. However, heterozygous new world female monkeys have trichromatic vision because of the polymorphic X chromosome gene, while homozygous female monkeys are dichromatic. Primates are divided into two different categories, New world (Platyrrhines) and Old world (Catarrhine). These two groups are distinguished by a couple features. The first and most important are their noses. Platyrrhines have flat noses that are rounded with nostrils pointed out. Catarrhines have long and narrow noses that point down. These two groups of primates were separated 30-40 million years ago. After this separated they began different evolutionary paths. It is thought that the mutation for trichromatic vision occured after this separation, as the ability to see red is clearer in Old world monkeys rather than New world monkeys. There are multiple theories that suggest what could have happened to allow or bring the need to see the colour red and become trichromatic. The first hypothesis is gene duplication. This duplication would have taken place after the catarrhine monkeys diverged from the platyrrhine monkeys. This hypothesis says that, “single X-opsin allele was duplicated in catarrhines and catarrhine M and L opsins diverged later by mutations affecting one gene duplicate but not the other. Platyrrhine M and L opsins would have evolved by a parallel process, acting on the single opsin gene present to create multiple alleles. Despite the homogenization of genes in the New World monkeys, there has been a preservation of trichromacy in the heterozygous females suggesting that the critical amino acid that define these alleles have been maintained.” (Herold, 2009) This is just stating that after the divergence old world monkeys duplicated differently than new world monkeys. Another hypothesis is the fruit hypothesis. This idea came from the notion that the mutation was needed in order for species to find food and survive. Many researchers have agreed with this hypothesis. The ability to see red provides an important advantage for any species who relies on fruit as their main source of food. Being trichromatic allows for the species to see when a fruit is ripe or notice some fruit, like apples, against a green foliage background. However, the issue with this hypothesis is that many trichromatic species eat leaves and seeing red would not help them with this. This issue could be disputed by the fact that the edibility of leaves is determined by maturity and this maturity is shown through colour. Emily Liman of the University of Southern California.proposed another hypothesis. She says that trichromacy evolved because of reproduction. When some old world female monkeys and apes fall into estrus ( a period of sexual receptivity fertility) they develop swellings and rashes that are red in colour. The ability to see the colour red would help signal the males when to reproduce since they have a poor sense of smell when trying to detect female pheromones. Although not one of these hypotheses has been verified or chosen as the right one, they offer many different reasons that are all possible. The reason this mutation occurred in primates could be for multiple needs. Even though we do not know why it occured we know that it happened and the same mutation transferred to humans. It was a very important trait that continues to help ensure survival for many different species.