Convergent Evolution Refutes The "Argument" For A Common Designer

The “argument” from design is basically nothing more than saying god did it. We often see strawman arguments comparing things like bicycles, that we know are designed, but don’t acquire mutations that are passed on to their offspring where they are selected with examples of organisms, which do accumulate and transmit selectable mutations. No matter what you say to a creationist, he will just say “ah well, that’s just the way god made it”. They can never predict how it would be. One piece of evidence for evolution is the existence of homologous structures in groups of organisms. These are structures built on a similar “blue print”. The classic example is the vertebrate limb, where the different bones can be identified in various structures from flippers to wings. Creationists of course claim that this is the work of a common designer and not the result of common decent. A problem in consistency then arises when you point out analogous structures (those that perform the same function, but are structurally different; the classic examples being the wings of birds and insects. Surely then the creationist should argue that this is then evidence of more than one designer – the problem of course is that they only believe in one god and pull an answer out of their assess like “god made it that way for a reason”, which really isn’t an answer at all. Using their straw man analogy further, the person (more accurately people) who designed your computer did not design the seat you are sitting on. Why then should we assume fish have the same designer as earthworms or palm trees? The creationist response of course is that their god did anyway – no evidence, just an assertion.

Although the planet “allows” life, it is not exactly life friendly. Life has many problems to solve – too hot, too cold, too wet, too dry, too much oxygen, not enough oxygen etc…. Sometimes we see different species “solve” the same problems in similar ways. Would we then not predict that a designer should engineer in the same solution?

Previously I posted on the loss of haemoglobin genes in ice fish as an example of evolution over a long period of time. These fish have another interesting adaptation; they produce antifreeze molecules. There are two unrelated group at either pole that produce nearly identical antifreeze glycoproteins (AFGPs). These are the northern Arctic cods (superorder Paracanthopterygii) and the Antarctic Nototheneiods (superorder Acanthopterygii). These proteins, which bind to and prevent the growth of ice crystals, are based on repeats of the amino acid sequence (threonine – alanine (occasionally proline)- alanine)n. The sugar galactosyl-N-acetylgalactosamine is covalently linked to each threonine in the repeat sequence. There are several forms of the molecules that vary in the number of repeats of these three amino acids, but they are all encoded by the same gene: there are sites in the protein that are later processed to produce AFGPs of different lengths. So, here we have two unrelated groups with almost exactly the same protein serving the same role – creationists must be cumming in their pants at this point.

However, if we look at the structure of the genes, there are significant differences. To recap, (eukaryotic) genes are composed of exons (that appear in mature RNA sequences) and introns (which do not encode for proteins and are chopped out of mature protein encoding RNA (which links protein encoding instructions from DNA to proteins). The gene from the Arctic species Boreogadus saida contains 3 exons (E1-E3 of Bs3-1 Figure1), whereas the gene from the Antarctic species Dissostichus mawsoni contains only 2 (Dm3L).

Another interesting feature is the sequence of an area called the signal peptide (this directs the newly synthesised proteins to particular areas in a cell). These are totally different – as can be seen from their single letter amino acid sequences.

Fig 1

One final difference is the actual gene sequences themselves. There is more than one way to code for most amino acids, and the sequence threonine – alanine – alanine can be encoded by the sequences (codons) ACA, ACT, ACC or ACG for threonine and CGA, GCT, GCC or GCG for alanine. What we find is that the codon usage is different in the two different genes. B. saida uses the codons ACA/ACT (45%/42% for Threonine)-GCA/GCG (51%/30% for the first Alanine and GCA/GCG (53%/37% for the second Alanine). D. mawsoni uses ACA (85% for Threonine)-GCG/GCT (39%/55% for the first Alanine) and GCA (95% for the second Alanine). Basically, the sequences are different suggesting a different origin. This similarity in protein sequence is an example of convergent evolution.

The original publication can be found here

One final problem for creationists is that a prediction of evolution is that genes arise from ancestral genes, so we should not be surprised to find a candidate and a putative mechanism for the evolution of these proteins. Guess what creationists, for D. mawsoni, the ancestral gene is trypsinogen. Part of this gene and the control regions seem to be duplicated. Not only that, a 9 nucleotide sequence encoding the threonine – alanine – alanine repeats appears to have been further duplicated (mechanism). This is detailed here.

Oh yeah, and all this is corroborated by paleontological and geological studies concerning the appearence of these fish and the timing of the opening up of the polar oceans.

And the creationist response? That’s right, “my goddidit!” No predictive model to test required – just a bronze age book of superstition.