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Sunday, January 20, 2008

Where Are the Missing Links?

I've just reposted an old entry from the old journal, and it reminded me of a point I wanted to make in that post so long ago.

Every so often, the creationist canard "there are no missing links" will reappear like a gunshot-tattered zombie. Creationists and anti-intellectuals alike appear to take weird delight in stitching together this smelly, rotten argument, as though they really expect it to pass (this time for sure!) though the chainsaws of scientists and laypersons who know better.

The problem is (to extend my metaphor to perhaps not-unreasonable extents), science has progressed beyond the chainsaw when it comes to dealing with these oozy and invalid arguments. With every new major fossil taxa uncovered (like Tiktaalik, Indohyus and Yanoconodon and so on and so on) as well as yet another molecular study of extant organisms revealing even more evidence in support of what is already one of the best supported scientific theories, science now has chainsaws and grenades and sharp sticks and particle beams and... well, you get the point.

But I want to beat up on the zombie, too. So I typed this, which perhaps might make a few creationists think twice before reaching for their sewing needles and scissors before they wind up with gross gobbets of gray flesh splattered all over their smocks.

The literature doesn't really talk about missing links for the simple reason that they don't really exist--I mean, there're just not missing ("missing," in the sense of creationist use, implies "not there").

Now there really are unknown ancestor taxa that would link known taxa, but since you can't really have a lineage without ancestors, the fact that the ancestor is unknowable is irrelevant. (Arguing that is it is somehow relevant is like suggesting that knowing exactly who the mother is of a bunch of kids is somehow necessary in order to identify the kids as being human.)

If it lived, it had an ancestor. What animal the ancestor is is actually unimportant. If the ancestor were known (by accident, because, again, ancestors are unknowable), it would simply be very closely related to its descendants, and therefore close enough at hand anyway.)

But the gist is this: cladistically, closely related organisms cluster closely together.

Distantly related organisms will have a range of intermediates (transitional forms). That is, many many links "separate" them.

So setting aside the uselessness of the "no missing link" argument, my rejoinder is: what's missing about the links? Since we find so many of them, it's really not possible to regard them as "missing."

1 comment:

Zach said...

Awhile back, I came up with an artistic method of reconstructing common ancestors that I have yet to actually put into practice. Take two basal members of two known sister groups. Say, Lesothosaurus and Eoraptor. Point out all the features they obviously share, and restore those. Take unknown traits from the more basal of the two taxa. In this case, a tri-radiate pelvis from Eoraptor.

This only works, of course, if you have a reliable outgroup (like Silesaurus) who can be useful in polarizing basal or derived characteristics in the taxa you're trying to ancestralize.