Deriving from the New Archaeology of the 1960s and early 1970s, processual archaeology generally takes an anthropological and positivist position. The latter has had strong implications for the manner in which archaeologists interpret the archaeological record. Through its paradigm of natural science, the past is imbued with a ‘naturalism’ in that social phenomena are regarded like natural phenomena: society is treated as a second nature. Drawing particularly on biology, systems theory became a dominant model in which to view the past, where societies are seen as systems with various parts, each interlinked most notably by feedback relationships. Ecological models are commonly invoked to explain various phenomena, and ‘natural’ factors, such as subsistence and the environment, play a strong role in explanation. Problems which are recognised include previous assumptions about what constitutes ‘efficiency’ in such systems, and therefore a wider interest in symbolic and cognitive spheres is developing.