People adopting independent manner (4)
I believe the answer is:
mien
'manner' is the definition.
(mien is a kind of manner)
'people adopting independent' is the wordplay.
'people' becomes 'men' (men can refer to humanity as a whole).
'adopting' means one lot of letters goes inside another.
'independent' becomes 'i'.
'men' placed around 'i' is 'MIEN'.
(Other definitions for mien that I've seen before include "Facial expression sounds miserly" , "A face - maybe mine" , "Appearance is strangely mine" , "A manner like mine" , "Person's appearance or manner" .)