Primal impulse (4)
I believe the answer is:
urge
'primal impulse' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for urge that I've seen before include "Try hard to persuade, advise earnestly" , "Encourage or entreat earnestly" , "Implore" , "Capital of Colombia" , "Press to take action" .)