Develops (7)
(Other definitions for becomes that I've seen before include "Turns into" , "Changes into" , "Suits, befits" , "Gets" , "Undergoes a change" .)
'develops' is the definition.
('evolve' can be a synonym of 'develop')
This is all the clue.
(Other definitions for evolves that I've seen before include "Develops gradually, perhaps over millennia" , "is on the increase" , "Develops by degrees" , "Gradually develops into over time" .)