Evolution does not increase a species’ implicit knowledge of the niche by replicating genes. Mutation (evolution’s conjectures) creates potential new knowledge of the niche. Selection decreases the “false” implicit conjectures of mutations and previous genetic models of the niche.
So induction does not increase the implicit knowledge of gene sequences.
Trial (mutation) and error (falsification) of implicit theories does. This is the process that the critical rationalist says happens but more efficiently with humans.
I don’t think he is saying, “good explanations are hard to vary while preserving their predictions”.
As described above the statement “Everyone just acts in his own interest” very easily preserves its predictive power in a multitude of situations. Indeed, the problem with it is that the statement preserves its predictive power in too many situations! The explanation is consistent with just about whatever happens, so one cannot design a test that makes one believe that the statement is certainly false. So it is too easy to vary and hence a bad explanation.