Hi Frank.
A lot of what music does is cultural, but the basic resources are inbuilt in the way the ear and brain process sound.
The choice of frequency intervals that all human cultures use is based on the fact that we hear frequencies logarithmically so that the interval between a note and one double the frequency is perceived as the same note only higher. All melodic activity goes on between these points. The ear evolved to deal with natural sounds of which most of the ones with the property of tone, consist of a series of frequencies linked in a harmonic way.
To cut a long story short the ear-brain system recognises as meaningful simple ratio intervals between 1/1 and 2/1. These intervals by definition will contain an odd number, and the degree of dissonance increases as the size of these numbers.
Thus
1/1absolute consonance
2/1 octave
3/2 fifth
4/3 fourth
5/4 major third
8/5 minor sixth
6/5 minor third
5/3 major sixth
.....
....
Maximum dissonance

All the best PP