In 1990, linguist Roger Lass transplanted an idea from evolutionary biology to historical linguistics: exaptation.
Exaptation is the repurposing of existing elements for brand new functions. In biology, the classic example is birds’ feathers: originally believed to have developed as heat-retaining insulation, they provided a convenient basis for flight. A lucky accident, if you will. And there are plenty of instances that fit that bill in language change.
Lass’ classic example involves the development from Proto-Indo-European to Proto-Germanic. PIE had a system of alternating vowels (called ablaut) to mark aspect in verb stems. For instance, a present stem might show -e-, while -o- signified perfect and -ø- (zero, or no vowel) was the marker for aorist. Ancient Greek actually preserved that pattern quite well, and Lass gives the examples:
- Present: leípo (I leave)
- Perfect: léloipa (I have left)
- Aorist: élipon (I left)
However, Proto-Germanic did something quite odd. Instead of using it to indicate aspect, it repurposes it to show number in the preterite tense. Look at these examples from Gothic:
- Present: beitan (to bite)
- Preterite 1ps: bait
- Preterite 1pp: bitum
Considering that -a- is the Germanic reflex for PIE -o-, here, we have the same alternation – -e-, -o-, -ø- – but representing something else entirely.
An Idea with Wings?
Cross-discipline metaphors rarely fit exactly like a glove, and it’s clear this isn’t quite like feathers being exapted for flight. For a start, feathers still fulfil both functions: a cosy coat as well as flying apparatus. In general, with exaptation, we’re talking about wholesale transformation of something that had ceased (or was about to cease) to be meaningful any more. Lass called this morphological ‘junk’ initially, but this has been a source of disagreement. Just what is ‘junk’ in a language?
Still, it’s a compelling metaphor, chiefly because it gets the imagination churning. How can things change so drastically in such a short time? What does language look like while it’s changing like this? Does it happen a lot? Can we see it happening now? Sometimes the best ideas are the ones that spawn more questions.
Exaptation hasn’t gained universal acceptance as a theory just yet, some three decades on from Lass’ initial paper. Some say it just boils down to reanalysis, like many similar changes. Others maintain that it’s a very particular direction of reanalysis, so it is unique and worth a place of its own in the textbooks.
Whatever its status, it does throw up some absolutely fascinating examples of extreme change.