FIGURE 3.4 The norm of reaction concept This classic figure illustrates how a given genotype can develop differently in different environments. Three cuttings were made from each of seven individual plants; thus, the cuttings in each set of three had identical genes. The three cuttings from each plant were then planted at three different elevations, ranging from sea level to high mountains. The question of interest was whether the orderly differences in height that were observed at the low elevation would persist at the two higher elevations. As you can see, the order of the heights of the plants is neither orderly nor consistent across the different environments. For example, the first plant on the left that is the tallest one at sea level and at high elevation is one of the shortest at medium elevation. The fourth plant is tallest at the medium elevation and shortest at the highest. Notice that not a single plant is always either the tallest or the shortest across the three elevations. “The phenotype is the unique consequence of a particular genotype developing in a particular environment” (Lewontin, 1982, pp. 22–23).