Full Idea
The dispositional theory of biological functions is not unquestioned. The main alternative is the etiological theory: a component's effect is a function of that component if it has played an essential role in the causal history of its existence.
Clarification
'Etiology' concerns causation
Gist of Idea
Rather than dispositions, functions may be the element that brought a thing into existence
Source
Bert Leuridan (Can Mechanisms Replace Laws of Nature? [2010], §3)
Book Reference
-: 'Philosophy of Science' [-], p.8
A Reaction
[He cites S.D. Mitchell 2003] Presumably this account is meant to fit into a theory of evolution in biology. The obvious problem is where something comes into existence for one reason, and then acquires a new function (such as piano-playing).