"one letter is changed at a time"

"The iconic graphical rendering is a three-dimensional ‘mountainous’ landscape in which genotypes are organized in the x–y plane and fitness is plotted on the z axis (FIG. 1a). In such a landscape, evolution can be seen as ‘walks’ and adaptation as ‘climbs’ to higher positions on the fitness surface.

Entretanto, no Domingo à noite li o trecho que se segue:

"For many years, the fitness landscape concept underwent little further development. One reason was the general lack of understanding of the molecular basis of adaptation and hence of the relevant ‘genetic units’ of the genotypic space. This changed when John Maynard Smith introduced the notion of mutational pathways in protein space. He used the analogy of a word game, in which a word must be converted into another word of the same length with the requirement that one letter is changed at a time and that all intermediates are meaningful words (for example, from ‘word’ via ‘wore’, ‘gore’ and ‘gone’ to ‘gene’). Given the low per-base-pair mutation rate, he argued that proteins also adapt by a series of single amino acid changes, in which all intermediate states must be functional for a trajectory to be accessible by natural selection."

E isto não me tem saído da cabeça... a relação com a frase de Hausmann: Os macacos não voam!