But this fitness has no benefit for cell or organism, only for the distorting allele itself. If there is any selective cost to the organism, the outcome of selection will depend on the balance between the direct advantage to the allele based on segregation and indirect cost due to selection against organisms containing distorting alleles. Selection distortion is only apparent when there are competing alleles. Once either a normal or a distorting allele is fixed, then there is no longer any segregation to distort. For some reason, Ridley avoids discussing selfish DNA in terms of the units of selection.
Cancer demonstrates selection favoring mutant cells at the expense of the organism.
The effect is so powerful that selection for organisms has apparently produced mechanisms to suppress such events. Selection among cells can also operate in plants which have multiple growth points, The favored meristem can overwhelm other branches, but the outcome can be beneficial for the entire plant. Most adaptations are traditionally understood as features which benefit individual organisms. This view is probably true. Natural selection working on groups of close genetic relatives is called kin selection.