 Johannsen, as noted earlier (and conveyed in the contrast between the method of  figure 2  and the theory of  figure 1),  provided no method to divide a natural varying population into phenotypes as classes of organisms, let alone to use these classes to identify genotypes as classes within such populations. What would be required then in order to apply his terms and distinction in the study of heredity for natural varying populations? A number of pathways can be delineated: 