In Darwinian theory which came first, the functional gene, or some non-functional precursor of the gene, perhaps co-opted from something else? How does one know what was co-opted from what?
Cordially,
L-GLO is an enzyme. The enzyme is found across the animal and plant kingdoms. That is a fact.
The protein sequences of L-GLO enzymes in widely different species are homologous.For example, here are the first 60 amino acids from the L-GLO of the mouse
MVHGYKGVQFQNWAKTYGCSPEMYYQPTSVGEVREVLALARQQNKKVKVVGGGHSPSDIAand here is the sequence from the cloudy catshark.
MDQGTMGYQFENWATTYSCEPELYFEPTTVEEIRQILELANQRNKRVKVVGCGHSPSDIA
So that, too, is a fact, and we can in fact mathematically quantitate the homology. We can construct a tree diagram, in fact, showing how close the sequences are to each other. What we find is that between the mouse and the rat, there are four differences; between mouse and pig, six differences; between mouse and cow, six differences; and between mouse and catshark, twenty two differences. And there are more distant homologies to other enzymes with similar but not identical functions. Those are all facts. What is also a fact is that the differences in the L-GLO gene mirror exacly the evolutionary distance between these species, determined by biologists before they knew the sequence.
So now, if I take the L-GLO protein, find its gene in the mouse genome database, and go looking for homologies in the human genome, what do I find? A stretch of chromosome 8 that contains large chunks very similar to the genetic code for my protein. Another fact. In fact, the sequence looks very much like a highly mutated, broken L-GLO gene. And L-GLO is absent in humans. Another fact.
Now, I grant you, the rest is inference.