by Matthew Law

MNI stands for minimum number of individuals, and is one of the ways in which archaeologists try to give meaning to the quantity of bones, shells or other biological remains of a single species in an assemblage. The MNI is the smallest number of living individuals which could account for all of the elements present of a particular species (Reitz and Wing, 1999: 194). As an example, if an osteologist studying human bones is presented with a fully-fused left tibia, a right femur and a right humerus, the MNI could be said to be 1, as all the elements could conceivably come from one individual. If, however, there were two right femurs, the MNI would be 2, as one person could not have had two right femurs. 

When reading reports which refer to MNI, it is important to emphasise that the number given is a minimum, and so should not be interpreted as an actual number of individuals (Reitz and Wing 1999: 195) nor even a most likely number of individuals (White and Folkens 2005: 339); in the example above, it is possible that all three bones may have come from different people.

The number of bones from a single identified species is not all that is needed to derive an MNI estimate.  Information about age or sex of the individual should also be considered (for example, are all the bones from an adult?), as well as the context in which the element has been found.

MNI estimates can also be used for shells. Different experts prefer to use different parts of the shell for this calculation, often the apex is used for gastropod shells, and the umbo of one or other valve used for bivalves, however Claasen (1998: 107) cites an example from the 7000-year-old  Dogan Point site in New York, where the lower valves of Eastern oyster easily exfoliated along growth lines, giving the appearance of an increased number of shells. In this case the top valve gives a more meaningful MNI.

As well as archaeological material, MNI estimates are also used on human remains in criminal investigations by forensic anthropologists.

See also NISP

References

Claasen, C., 1998, Shells. Cambridge: Cambridge University Press 

Reitz, E.J., and Wing, E.S., 1999, Zooarchaeology. Cambridge: Cambridge University Press 

White, T.D., and Folkens, P.A., 2005, The Human Bone Manual. San Diego: Academic Press

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