The three primary colors of life-Scientific knowledge
Human studies of color can be traced back to the two fathers of science: Newton, the father of physics, and Dalton, the father of chemistry. Newton first discovered in the mid-17th century that through the refraction of the prism, the white sunlight became as colorful as a rainbow, that is, white light is actually a mixture of light of several different colors. In the eighteenth century, scientists have known that different colors, such as red, blue, and green, can form all the colors that humans can perceive. If the light of these three colors is mixed in equal amounts, it becomes White light. These three colors are therefore called the three primary colors.
In 1774, Dalton announced that he and his brothers had discovered red-green blindness: their color world was not composed of three primary colors, but only composed of yellow and blue colors. They can't see red and green. In the nineteenth century, physicist Thomas Young proposed a bold hypothesis that the so-called three primary colors are because humans have three independent photosensitivity mechanisms, and color blindness is due to the failure of one or both mechanisms. Subsequent studies of color blindness validated this hypothesis. Despite the existence of many kinds of color blindness, the results of the research indicate that they are all due to the inability to feel one of the three primary colors of red, blue and green, with red and green blind being the most common.
This hypothesis was finally confirmed by modern biology.
Originally in the retina of vertebrates, there are two types of photoreceptor cells. According to their shape, we are called rod cells and cone cells. Rod cells are used to feel the intensity of light and can't feel color. This kind of cell only works when the light is weak. When the light is too strong during the day, the rod cells are inactivated and gradually recover in the dark. Cone cells, on the other hand, are used to sense color and only work when the light is strong. If you walk into the dark from a brighter place, you will suddenly feel blind, because the cone cells are no longer working, and the rod cells will take a few minutes to begin functioning.
For animals that only sleep during the day and sleep at night, such as squirrels, they only have cone cells and no rod cells; those that crouch in the night are the opposite, only rod cells and no cones. Human rod cells are much more than cone cells, with more than 100 million rods and six million cones (the receptors of these cells account for 70% of all receptors in the body, and the importance of vision to humans is thus visible ), but rod cells are only distributed around the retina, not at the center, while cone cells are concentrated in the center of the retina, so usually cone cells are at work. In the dark, if you stare directly at the same thing, the light falls in the center of the retina, and you may not see it clearly. If you look at it obliquely, let the light fall on the edge of the retina where the rod cells are concentrated, but you can see it clearly. Astronomers have known this way to observe stars with very low brightness long before we discovered rods and cones.
There are only one kind of rod cells, but there are three kinds of cone cells, which are red, green and blue pigments (see protein). They can sense red, green and blue light. The generated nerve signals are transmitted to the brain. We will see In a colorful world. If there is a cone that is not present or defective, there is one primary color missing in your visual world.
These three pigments, as well as rhodopsin in rod cells, are expressed by different genes. These genes were discovered a few years ago. The four pigment genes are located on three chromosomes, the rhodopsin and blue pigment genes are located on chromosomes 3 and 7, respectively, while the red and green pigment genes are linked together and are located on the X chromosome. As you know, a man has only one X chromosome, and it will show up when something goes wrong. Unlike a woman who has a pair of X chromosomes, one out of the case will be covered by another, so red-green blindness is a sexually linked genetic disease. There are many more men than women.
The sequences of the red pigment gene and the green pigment gene are very similar, 98% identical, and it is clear that they evolved from the same gene. In fact, there are certain similarities among the four pigment genes. The calculations show that they were evolved from the same gene about 500-100 million years ago, while the red and green pigment genes are relatively late. It happened only 40 million years ago. In other words, 3-4 million years ago, the eyes could not distinguish between red and green, and everyone was red and green blind.
Unexpectedly, the number of genes for green pigment in men is not fixed. For most men, there are two green genes and one red gene, ie the ratio of these two genes is 2:1, but It is not uncommon for the ratio to be 1:1 or 3:1. The difference in the proportion of these two genes causes the male to have a variability in the perception of red and green. Does the existence of this mutation indicate that the green pigment gene is evolving into two new pigment genes? In that case, we will have four primary colors, and what would a world of four primary colors look like?
