Initially this seems to be fairly straightforward: some kinden are, and always have been, apt; whereas others fulfill the same role for the inapt.
Gradually, however, more information is revealed:
- There is at least one inapt Wasp
- Skater-kinden have both apt and inapt members, and the ratio is changing
- Woodlouse-kinden also have a mix but some of the most philosophical claim to be both
- Two characters changes from apt to inapt over the course of the series.
The whole thing now appears to be a particularly complex subject, with few options not explored.