Make a great effort to find the ancestry (6)
I believe the answer is:
strain
I believe this clue is a triple definition!
'make' is the first definition.
(I know this)
'a great effort' is the second definition.
(I've seen this in another clue)
'to find' acts as a link.
'the ancestry' is the third definition.
(strain is a kind of ancestry)
(Other definitions for strain that I've seen before include "Exert oneself to the utmost" , "Pressure - filter" , "Stress or make taut" , "Distinct breed; use a seive" , "Overtired" .)