'Exaptation' is probably one of my favourite words in the biologist's dictionary, but outside of the discipline, it's not very well known - which is upsetting because it's a particularly useful word that would be well suited to a philosopher's lexicon. So what is exaptation? To begin with, it's meant to be distinguished from an 'adpatation': where an ad-apatation is a feature or trait selected for by natural selection because of it's usefulness at fulfilling a particular function (survival, in the broadest context), an ex-aptation is a feature or trait which, while 'originally' used for some function or another, has been co-opted or re-purposed to do something other than it was originally evolved for.

The usual example are feathers. As the evolutionary story has it, feathers were originally evolved for the sake of insulation and warmth, before later being exapted for the sake of flight, which they happened to be particularly well suited to. The 'opposite' of ex-aptations, by the way, are 'vestigial features', like your appendix. The appendix is a 'vestige' or a 'remnant' of a part that at one point probably played a role in digestion, though no longer. Things are slightly complex here because the appendix also has 'exaptive' features: although it no longer does digestive things, it now plays a role in helping to maintain our gut biomes - the environment for our gut bacteria.

So, what kind of philosophical significance can be drawn out of these terms? Well for one thing, the idea of an exaptation was originally introduced to highlight the role of contingency in evolution. As Gould and Vbra (the evolutionary theorists who coined the term [PDF]) put it, "all exaptations originate randomly with respect to their effects" (emphasis in the original). The concept of exaptation then, helped to bring into evolutionary consciousness the idea that evolution largely works by jury-rigging alot of its results: it makes use of features or traits that were 'lying around', as it were, in order to plug them into different contexts and modify their 'original' uses. In a sense, all creatures are products of just this kind of evolutionary tinkering, building upon past-results to achieve new ends.

(Which is not always a good thing: it's often said human brains, because they were so clumsily put together - a result of a 'kludge', a haphazardly thrown together, inelegant assemblage developed across the span of literally centuries - just isn't great at strict reasoning, often relying on faulty heuristics to arrive at cognitive results).

It's telling too that biological structures can exhibit both exaptive and vestigial aspects at the same time, as through any 'pieces' of biology are just so many cogs and levers waiting to be plugged into different contexts in order to do different things. What matters is that function is not a principle but a result. Anyway, the larger point - and to pick up on the 'machine' metaphor - is that is useful to extrapolate the idea of exaptation to a cosmic principle: to see organisation - social, ecological, biological, astronomical, even - as a matter of just this kind of haphazad, contingent coming together of things, in which results build off the back of other results, retro-actively modifying their function, and intro-ducing new things into the universe as a result.