I came across a creationist (sensu lato) blog that I’d not noticed before: Todd’s Blog (subtitled It is the glory of God to conceal a matter; to search out a matter is the glory of kings. (Prov. 25:2) just so you know where he’s coming from). In an amusing posting, he’s discussing the signalling protein Notch, following up on a posting by another blogger – Quintessence of Dust – Deep homology and design: why Notch?). Of course, Notch is widely found across taxa, and I suppose is a classic evidence of evolution (it was originally identified in Drosophila, where the original mutants identified caused notching of wings). As Todd points out, it’s strictly speaking incorrect to say that different taxa have the same gene: he correctly says that all these taxa in which Notch has been identified actually have homologous genes.
Here’s where he goes a little off track: he describes homology as similar. In actual fact, the term homology carries with it the sense of similarity as a consequence of shared ancestry. See for example the Wikipedia entry for homology (biology).
Strange really. He very conveniently includes a diagram which illustrates the ancestry of various Notch homologues (see below).
A phylogeny of Notch homologues
What’s interesting here is how Todd wanders around the subject of shared ancestry:
I reject the notion of functional requirement and historic contingency, so that leaves the preference of a designer. The question is why? For what purpose did God arrange Notch proteins in that particular pattern?
(He’s quoting another blogger’s three possible explanations: that it’s the only functional option, it’s contingency, and that it reflects the action of a creator.) In point of fact, the small section of sequence alignment Todd presents is probably not too helpful: generally such sequence alignments reveal segments of sequence which are more conserved that others. These conserved segments reflect function: they are conserved because their sequence is constrained by function: change an amino acid residue and you alter the shape or biochemical characteristics of that region of the protein and affect its function.
So, strangely, Todd’s making an argument for evolution here: he’s noting homology between protein sequences of different taxa, shows how these sequences can be assembled diagrammatically to reflect the evolutionary relationships between taxa, but then chucks all that away because it conflicts with his prior beliefs. Todd goes on to say:
At this point, someone usually raises the idea that God would be deceptive if He created things to look like evolution if they didn’t really evolve. There’s lots of responses to that, but I’m going to stick to the theme and think more carefully about proteins. The truth is that the neat, clean pattern above is something of a rarity in protein homology. More often than not, the pattern of similarities observed in proteins does not make much sense in terms of organismal evolution.
I don’t think he’s correct here: the majority of cases I see in the literature is of protein sequence similarity that does make sense in evolutionary terms. Indeed, cases where this isn’t the case (for example because of horizontal gene transfer) are flagged up because they are so unusual. It’s a shame Todd sees the evidence but discards it in favour of superstition.