Earlier chapters specialized in a few model organisms, including the λ phage and its host E. coli. This choice was a modeling choice that reflected a historical contingency in the scientific community starting in the early 1950s. However, in spite of its random origin and positive social feedback  the scientific focus had advantages. A precise description of one model system may well have been more informative about the universal mechanism of gene regulation than a listing of various properties of different organisms. However, a prominent and astounding feature of life is its diversity; a diversity of species, strategies and molecular mechanisms.
Phage predation strategies
The approximately 1031 − 1032 phages in the world [129, 133] come with many forms, shapes and strategies (see Fig. 12.1 for an attempted family tree). The hierarchical relationships implied by this tree may not reflect the evolutionary relationship between all genes in the respective phage, since phages exchange genetic material extensively, both with each other , and between their respective hosts [616, 617]. This non-hierarchical relationship with gene transfer of groups of related genes is emphasized in Fig. 12.2.
In the upper middle branch of Fig. 12.1 one finds the λ phage, which has multiple close relatives, e.g. the ø80 phage  and the 434 phage are both similar to λ.