I suppose it would be easier (and require less, if any, actual thought) if I just said a kind is a kind, and left it at that. However, I can't do that.
Why not?
Why does it matter what the extremely specific definition of 'kind' is?
The Bible doesn't provide one. Why can't it remain a general term? A 'kind' would be a grouping of animals that brings forth the same thing as itself.
If you take it down to the speicies level, then there's too many of them to fit on an ark. If you bring up to, say, the family or genus level, then there'd be too much "hyper-evolution" to get the diversity we see now today.
I suppose the most bestest definition could be found, though. Say we have a sliding scale between the number of kinds we would have, where on one end it would be if we used 'species' and on the other end if we used 'family'. If slid too far to the left, they don't fit on an ark, if slid too far to the right, there's too much diversity today. We'd have to find the optimal place to put the slider so that they could all fit on an ark, but we don't have too much diversity today.
I think that
that definition of kind would not fit nicely with our current classification system, whereas sometimes kind would fit with a whole family, sometimes it would fit with a genus, and sometimes it would fit with a species.
And at the end of the day, what would we really have accomplished?