I reckon that if you start with your index finger on the 4th fret low E string (G-sharp) and then play the next 3 frets with middle, index, pinky then drop down and repeat the same pattern on the remaining strings you have played a chromatic scale. So basically 4 notes on each string in exactly the same position using the same fingers. Now if you learn the intervals of a major scale you will miss out some of those notes and hence some of you fingers, so, for example, to play the A major scale you would start on 5th fret bottom E, middle finger miss a fret as it is a whole step to B which would be your pinky. Drop down to the next string, you now need another whole step which is C-sharp. That would be 4th fret on the A string played with the index finger. Half a step now so middle finger on the 5th fret and so on. The fingering is logical. You need to learn the intervals and notes on the neck.