On The Panda's Thumb "lurker" asks:
...can Calvert show us how to figure out how something was Designed?
The best my poor brain can come up with is that designed systems are distinguished from "accidental" systems by identifying Design Intent. An axe head may be distinguished from a random piece of fractured chert, with some degree of certainty, by understanding what an axe head maker would have intended, based upon the list of Critical and Significant Design Characteristics For Axes (perhaps as specified by the Axe Users' Focus Committee), and evaluating whether it fulfills the requirements to a sufficient degree. (Requirements fulfillment "sufficientness" criteria TBD.)
But that creates its own set of problems.
In describing complex dynamical systems that result from a non-directed evolutionary process one cannot, strictly speaking, talk about "purpose" or "function" at all. Elements within a given system exist, they exhibit characteristics and/or behaviors, and these have effects on other parts of the system. Often those effects are such that they tend to create conditions that cause the elements to persist (or, at least, do not create conditions that tend to make the elements disappear). Dung beetles e.g. have no "function" in an evolved ecological system; they simply exist, and their existence and behavior have some beneficial side-effects for other elements of the system, which ultimately results in dung beetles having an easier time making a living -- so, the beetles persist.
Scientific investigation of evolved systems is a descriptive process. That is, the researcher observes the system, enumerates the activities and characteristics of its elements, and attempts to identify and understand the web of effects that the elements have on each other, which in the end determine the way the system itself, taken as a whole, behaves over time.
In complex systems that have been designed, one must talk about "purpose" or "function"; those are primary distinguishing elements at any point in the analysis. The system itself exists because one or more Designers specified its composition in order to achieve some goal or objective. Dung beetles, in a designed ecology, would be there specifically in order to handle problems resulting from accumulation of ruminant wastes, in the same way that a catalytic converter is present in an automobile specifically in order to handle problems with undesired compounds in the engine's exhaust.
Investigating designed systems is fundamentally a prescriptive process; we are less interested in what something does than in what it is supposed to achieve. In looking at human designs, for instance, the focus is on what the designers intended to accomplish, and how well the designs they created perform when measured against the design goals. Always in front of one is the Design Intent which ultimately prescribes what the designed system must do in order to be judged successful.
At this point it must be understood that "purpose" or "function" of a given system can only have meaning within the context of the larger system that encloses it. And the purpose of the enclosing system can only be understood within the context of the system of which it is an element. It's Turtles All The Way Up, until one eventually reaches either an enclosing system that was not designed, or the limits of the observable universe.