}
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Bacteria are under severe predation by phage (Thurber, [@B29]). They need to constantly change to evade predation, hence the analogy to the red queen from Lewis Carroll\'s (Carroll and Gardner, [@B4]) *Through the Looking-Glass*, who needs to run as fast as she can just to stay in place (Van Valen, [@B30]). The analysis of phage metagenomes and rank abundance curves indicated that the phage predation follows the *kill the winner* strategy (Hoffmann et al., [@B14]), where successful strains are targeted more frequently. The surprising long term stability of species composition despite phage predation suggests that cycling between different susceptible target cells occurs within a population and not between populations from different species (Rodriguez-Brito et al., [@B25]). Consequently, within a population, host genes that encode receptors utilized by phage and virus to enter the cell are expected to turn over quickly, creating within population diversity (Chaturongakul and Ounjai, [@B5]).

Random acquisition of genes {#s5}
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Genes are constantly acquired by genomes, and many of the transferred genes do not find a long term home in the recipient genome (Lawrence and Ochman, [@B18]). Among these genes are parasites (prophages) and selfish genetic elements. Most, but certainly not all (Lobkovsky et al., [@B20]), of the transferred genes are selectively neutral or nearly neutral to the recipient (Gogarten and Townsend, [@B12]; Baumdicker et al., [@B2]; Haegeman and Weitz, [@B13]). Though these genes may not find long term homes in the genomes they "visit," selfish genes especially can affect the rates of gene sharing and thus the size of the pan-genome in a population. Furthermore, many selfish elements induce genome rearrangements that can promote the loss and gain of genes, and thus may have a significant impact on the initiation of the loss of leaky functions.

Generation of paralogs may play a role in facilitation of loss of leaky functions. Additional copies