For human beings, the visible spectrum is light with wave lengths ranging from approximately 400 to 700?

It is correct that the visible wavelengths of electromagnetic radiation are from 400nm (violet) to 700nm (red); but that is because of the way the eye perceives light, and has nothing to do with the way waves interact with each other. Also, because of the way the eye sees color (and not due to the nature of the waves) many colors can be produced either by a single wavelength of a combination of two or more wavelengths. For additive color reproduction three primaries are selected (red, blue and green) because they produce the widest range of other colors (gamut), probably because of the way the eye works. Other primaries can be used, but they will result in a more limited range; also more primaries can be added to increase gamut. How selected primaries are combined to create other colors is shown in the "CIE color chart".

The light receptors called cones, located in the retina of the eye, are responsible for our color vision.

Cones come in three types, each sensitive to a certain RANGE OF LIGHT WAVE LENGTHS.

The sensitiveness is due to the chemical pigment they contain.

One type of cone recognizes certain wave lengths as aspects of the blue color; others see only green and others as red.

These three colors are in a way the eye's primary colors, and mixing them together in the eyes,” palette' forms all the other colors.

From the cones color signals pass farther into the system, where neurons along the visual path mix and match them until we can see the full spectrum of about 5 million colors that make them up world as we know it.

If a wavelength corresponding to yellow falls on the cone, the eye recognizes it as either more blue than red or more red than yellow depending upon its wavelength and the range to which the cones are sensitive.

Most animals see a similar spectrum as human beings, some with some small extensions into infrared or ultraviolet. This has a simple reason: That's a window in the opacity of water. You can't see infrared or ultraviolet light though water, nor radio or radar. The nature developed the concept of eyes under water, so it was useful to chose that range of frequencies. Even on land it's useful to use that, as air contains a lot of water. During the evolution some animals (for example bees) extended that range , because it's important for them to identify flowers, and they have a characteristic appearance in the UV range. Another reason is that the atmosphere is not very transparent for UV light, so in that range it is, compared to the visible spectrum, quite dark on earth.

The interference of the wavelengths of red and green add up to give you the wavelength of yellow.

when two lights of different wavelenght coincide there is no interference because for interference to occur the two lights have to be coherent ie they should have the same frequency and their phase difference should remain constant with time which is not possible if their wavelenghts are different

There's no question there. Just a statement. What do you want to know?