These two categories can be traced back to the origin of life itself and to understand Daniel Dennett’s cryptic statement, “Natural Selection is thus an automatic reason-finder,” you first must understand how Dennett views reasons.
Reasons provide answers to the questions of why? However, the question why? is subdivided into two categories of what for? and how come? (38). When someone asks “why are your eyes blues?” they are really asking “what causes you to have blue eyes?” or rather, “how come you have blue eyes?” How come? questions seeks the process that explains the occurrence / observation, i.e. a kind of continuity. Understanding how come? questions is the first step in reasoning’s evolution and do not attempt to explain purpose or function (38).
Answers to what for? questions attempt to explain purpose and function (40). What for? seeks to understand function, and then provides meaning of that function in the larger narrative of the occurrence / observation. When someone asks “why are you writing this article?” they are really asking “what is the function / purpose of writing this article?” or rather, “what are you writing the article for?” What for? questions evolve out of how come? questions (40). Once causes are understood from how come? questions, further what for? questions are asked to understand purpose and relevance; the combination of both sets of reasons yield design and purpose.
Dennett’s objective is to explain evolution through Natural Selection by means of reverse engineering—not only reverse engineering our physical observations but also the way we think (design stance), and the way we ask questions and provide answers (intentional stance). Natural Selection starts with how come? reasons and moves to what for? reasons. By showing “how our human world filled with reasons grew out of a simpler world without reasons,” (38) Dennett is paralleling a world filled without purpose (bacteria) growing into a world filled with purpose (multiplying / reproducing organisms).
“The biosphere is utterly saturated with design, with purpose, with reasons (36)… Evolution through Natural Selection is not itself a designed thing, an agent with purposes, but it acts as if it were—occupying the role vacated by the Intelligent Designer” (37). Thus, Natural Selection is an automatic reason-finder (49); over time building reasons from the bottom up, rather than the top down.
Dennett, Daniel. From Bacteria to Bach and Back: The Evolution of Minds. WW Norton & Company. 2017.