Thanks John, for your patience in explaining. I don’t mean to belabor in order to argue, but I’m still struggling with this question that I have regarding parsimony and its role in an evolving species. What I’m gathering from what you have said is that, when one observes an organism that has a function that is not fully developed, that the assumption (based upon parsimony) is that this function is vestigial or the recurrence of a function that had formed earlier in the historical lineage of that organism. Is this basically correct?
If so, it seems to me that every function that formed over time (legs, fins, organs, etc.) would also fall under that same rule of parsimony. If a new function or feature rarely forms, and every feature or function was once new, then it seems that you would always be looking for new functions, because every function formed newly, once at least, in the past. Let’s say that the earliest common species for several classes of animals was a worm-like animal that had some sort of skeleton. (Maybe a very simple snake would be a better example.)
Since, from that snake, creatures with limbs, complete with upper and lower legs, knee joints, feet, toes, tarsals, etc., would have descended, it seems like we should also be looking for (and expecting to see) this process continuing today. As you said, this does not occur instantaneously, but rather over a long period of time. But if parsimony leads us to believe that new functions (features) are rarely added, we must have overcome that rule many times over.
That it is easier to recycle an existing function (feature) into something novel makes sense. That parsimony would apply also makes sense. That the diversity of function that we see, much of which was once novel, overcame that obstacle (parsimony) does not make sense to me.