Social science research, initially work included in collection of writings (12)
I believe the answer is:
anthropology
'social science' is the definition.
(anthropology is a kind of social science)
'research initially work included in collection of writings' is the wordplay.
'initially' says to take the initial letters.
'work' becomes 'op' (abbreviation for opus).
'included in' means one lot of letters goes inside another.
'collection of writings' becomes 'anthology' (I've seen this before).
The first letter of 'research' is 'r'.
'r'+'op'='rop'
'rop' placed into 'anthology' is 'ANTHROPOLOGY'.
(Other definitions for anthropology that I've seen before include "Study of human beings and their way of life" , "Study of humankind" .)