Figure 10.13: Why high within-group heritability tell us nothing about group differences In this example the same genetically diverse mix of wheat seeds was planted in two fields. Within each field the environment is quite uniform (same thickness of topsoil), so the differences in plant size are mostly the result of differences in genes (high heritability). However, the difference between the two fields in average plant size in this case cannot result from genes because genetic differences would cancel out in the averages; it must result from differences in the environment.