 Some biologists used the term pre-adaptation to capture the idea that a trait selected for one function may turn out to be very useful for something else. However, Gould and Vrba (1982) introduced the term ‘exaptation’ to capture such transitions, and avoid what they saw as the overly teleological implications of pre-adaptation, as well as to recognize that non-selected traits of organisms could also be co-opted to serve a function, increasing fitness without having any further modification by natural selection (Lloyd &amp; Gould 2017). Critics of the etiological natural selection approaches sometimes argue that backward-looking approaches are too vague with respect to questions about the point at which traits acquire or lose functions, and that they are consequently untestable empirically (Amundson &amp; Lauder 1994). Godfrey-Smith (1994) independently proposed a “modern history” theory of functions to address these problems. Similarly, Griffiths (1993: 417) invokes a notion of the “last evolutionarily significant time period” to handle these issues, but many critics remain unconvinced (e.g., Wouters 1999; Davies 2001). 