Observations on the history of zooarchaeological quantitative units: Why NISP, then MNI, then NISP again?

Suggestions regarding the history of use of zooarchaeological quantitative units known as the number of identified specimens (NISP) and minimum number of individuals (MNI) have previously had little empirical substantiation. Analysis of the North American zooarchaeological literature that appeared between 1900 and 1999 indicates there was (i) an increase in the use of MNI relative to NISP between 1900 and the 1970s, (ii) a subsequent decrease in the use of MNI and increase in the use of NISP, and (iii) an increase in the use of both NISP and MNI in the same publication after the 1970s. Inspection of a sample of articles indicates the last is the result of a shift to research questions requiring use of both units and also unresolved weaknesses in both NISP and MNI as measures of taxonomic abundances. The former reflects increased inquiry into taphonomic histories, the latter reflects the volume of programmatic literature evaluating strengths and weaknesses of NISP and MNI that peaked between about 1975 and 1995, and subsequently decreased with no clear consensus. Zooarchaeology textbooks of the last two decades present mixed signals regarding which quantitative unit to use.