Why does violet light (very short wavelength) appear purple (mixture of red and blue)?

Human have red, green and blue cones to distinguish color. Excitation of the red and blue cones makes the brain perceive purple. But light of shorter wavelength than blue (violet) excites only the blue cones and looks purple. Why?

Why does violet light (very short wavelength) appear purple (mixture of red and blue)?
As you can see on the page below, the "red" receptor has two maxima for its sensitivity, one in the red range (the main sensitivity) and a minor sensitivity range in the violet range. Hence, violet light stimulates the red and the blue receptor simultaneously.



I wonder if this has an evolutionary advantage, or if it's a biochemical necessity, or if it just evolved like this by chance.



Birds and reptiles have partly different kinds of color receptors than we have. It's quite possible that birds ands reptiles do not have this characteristic. If their red receptors are not sensitive to violet light, they will not perceive red as close to violet and hence have no notion of a "color circle".