Cziko explains how Darwinian selection can be applied or extended to many areas outside its traditional domain of biology to explain various puzzles of "fit" ranging from the immune system to the development and functioning of thought and the acquisition of knowledge. He gives an interesting perspective on education: if we learn and think by producing many varied solutions and selecting among them, then error and participation are essential to learning.
Also included is discussion of the early contributions of Donald T. Campbell on selectionist theories of thought, mind, science and culture, and Karl Popper's selectionist philosophy of science.
The general theme is that an evolutionary epistemology is broadly applicable and should be taken more seriously by those outside of biology. The book reads easily and is less didactic and polemic than Dennet's (though I like Dennet's polemics!)