- However, anagenetic changes can complicate the reconstruction of cladogenesis. If anagenesis occurs similarly in two distant phylogenetic lines under the influence of the same selection pressures, even unrelated species of organisms may have similar appearances. Then we could have a tendency to place these organisms close together on the tree. This approach is obviously erroneous; the cladogenesis scheme must express only the degree of mutual relatedness of organisms, while the degree of their phenotype similarity should not have any effect here. If the mutual phenotype similarity of individual groups of organisms is expressed graphically, a phenogram is obtained. The topology of a phenogram allows us to estimate which of the compared species exhibit similar properties and thus were, during their evolution, probably because of a similar life style, exposed to similar selection pressures. In cases where, for some reason, we cannot reconstruct the progress of cladogenesis, for example when all the studied species evolved during a historically short period of adaptive radiation (see XXVI.2.1.1) and did not further undergo speciation, or when all the species were formed gradually but from the same parent species, the phenogram can act as a basis for taxonomic classification of the given group of organisms. If a phenogram is formed on the basis of selectively neutral traits which change in all the phylogenetic branches at approximately a constant rate, i.e. for example on the basis of mutations accumulating in pseudogenes, i.e. in genes that have lost any biological function due to some critical mutation, and, if there is a sufficient amount of data, the topology of the phenogram should be identical with the topology of the graph describing cladogenesis. In this case, the phenogram can also be used for reconstruction of the course of cladogenesis.