This means that classification trees should reflect descent. The views of different schools that do not hold this view vary from acknowledging evolution as important, but not a practical base of knowledge on which classification can be based, to the view that classification is a discipline with its own value regardless of evolutionary theories. Benzon refers only to those that do hold the view that taxonomic classification must reflect phylogeny, for instance Mayr, leaving out members of other schools of thought. Biological evolutionary theory and species Benzon uses species as the sole example of biological evolutionary theory. Species are by definition sexually reproductive units, but most organisms reproduce asexually and cannot be classified as species per se.
Examples are bacteria, viruses, and many plants and lower animals.
Thus, only to speak of species as examples of evolutionary biology is not representative of empirical reality. Asexual reproduction is very important in biology. Borrowing is more common in the asexually then in sexually reproducing organisms. Therefore, it must not be overlooked in the discussion of the prevalence of borrowing in biological and cultural evolution. In biology, viruses can transmit genes over lineage-boundaries, and in bacteria plasmids are exchanged between strains.