Make an effort to find the ancestral line (6)
I believe the answer is:
strain
I believe this clue is a double definition.
'make an effort' is the first definition.
(I've seen this before)
'the ancestral line' is the second definition.
(I've seen this in another clue)
'to find' acts as a link.
(Other definitions for strain that I've seen before include "variety" , "Overwork - melody" , "Trains under stress and pressure" , "Force - melody" , "Muscle injury - tension" .)