Ok, how about a slightly different spin on it then.
Build a timeline of the significant developments in bass construction[list]
[*]Pickups
[*]Circuitry
[*]Strings
[*]Neck Construction
[*]Body construction (chambering etc)
[*]Outboard equipment, DI's, effects pedals etc..
[*]Fretboard developments - Fretless, fretted, impregnated..
[/list]
...and instead of saying how the sound actually changed, perhaps describe what new opportunities arose for bassists to alter their sound