4 ideas
By the 1840s roughly three million Irish poor lived almost entirely on potatoes, largely a single clonal variety (the Lumper), grown on tiny conacre plots rented in exchange for labour. Salaman treats the famine not as a natural accident but as the predictable collapse of a social system built on one crop.
Because an acre of potatoes could feed a family on a scrap of marginal land, the crop let landlords and employers pay subsistence-level wages and subdivide holdings ever smaller. The potato's efficiency did not raise living standards; it lowered the floor at which labourers could survive, allowing population to rise while wealth was extracted by others. A food that makes survival cheap can become the instrument that keeps people poor.
Potatoes are grown from tubers, not seed, so a whole region's crop can be genetically identical copies of one plant. This makes yields uniform and predictable in good years but means a single pathogen able to attack that genotype can wipe out everything at once. The efficiency gained from uniformity is paid for with fragility against novel shocks.
Salaman reads the history of a crop by asking what forms of land tenure, family size, labour relations and state power it made possible, rather than treating it as a mere foodstuff. Seen this way, the adoption of a staple reshapes demography and hierarchy, from Inca terraced agriculture to European peasant economies. Tracing how a society feeds itself reveals its structures of dependence and control.