Paul Nelson responded here to my post on “Intelligent Design and Common Descent.” Thanks, Paul. I had someone ask whether, in the piece we’re talking about, I meant universal common descent (UCD) or more limited common descent. I favor the latter, if any common descent is true. Note the qualification. The discontinuities are real. I think it’s all guided, and that probably it’s a combination of both descent with modification, and changes not by descent but by leaps.

But signals for common descent are also abundant in genomes. Within-group guided common descent might be possible. At what level of group is up for discussion, and requires much study. The guidance could well include the introduction of new genetic material or the conversion of existing material to function. We have focused so much on the differences. I think we also need to examine the similarities, and see how extensive they actually are.

I am not saying any change is possible that requires four or more neutral mutations to acquire a new beneficial function. Anything like that requires guidance. But note, guidance does not rule out common descent.

The Point of Intelligent Design

The whole point of intelligent design is that there is a need for a guiding intelligence to produce what we see in life. It does not specify in what context the guidance happened. Just that it did. I realize that many ID people are committed to a non-common descent view. They have legitimate arguments. I also know there are some who accept design and common descent. They also have good reasons. Might this not be telling us something? I am uncomfortable with blinding ourselves to any of the evidence.

I have been among those who argue against common descent.  I now think that the argument that genomic similarity is due to common function needs reworking, because there are so few examples. Certainly we have many fewer examples than there are needed. Our Achilles heel are things like pseudogenes, and patterns of ERV and SINE and LINE insertions. That and synteny. A case can be made that these are there for functional reasons. I have made that case. But we need more evidence. If this evidence is combined with discontinuities then our case against common descent will be much stronger.

Photo: Midge chromosomes, by Dr. Josef Reischig [CC BY-SA 3.0 ], via Wikimedia Commons.