reductionism

Concise Oxford English Dictionary © 2008 Oxford University Press:
reductionism/rɪˈdʌkʃənɪzəm/

▶noun often derogatory the practice of analysing and describing a complex phenomenon in terms of its simple or fundamental constituents, especially when this is said to provide a sufficient explanation.

– derivatives
reductionist noun & adjective,
reductionistic adjective.