Our old relatives this person put in an enclosure (6)
I believe the answer is:
apemen
'our old relatives' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'this person put in an enclosure' is the wordplay.
'this person' becomes 'me' (the person writing).
'put in' indicates putting letters inside.
'an' becomes 'a'.
'enclosure' becomes 'pen' (pen is a kind of enclosure).
'a'+'pen'='apen'
'me' inserted within 'apen' is 'APEMEN'.
Can you help me to learn more?
(Other definitions for apemen that I've seen before include "Our predecessors" , "Extinct human ancestors" .)