Two science articles worth noting.
The first talks about codon expression speed And the 23nd talks about horizontal gene transfer in humans.
1. The first suggests that codon’s express themselves at different speeds for different purposes.
“The most significant breakthrough in the Case Western Reserve work is that all of the words, or codons, in the genetic code are deciphered at different rates; some are deciphered rapidly while others are deciphered slowly. The speed of how mRNA decodes its information is the sum of all the codons it contains. This imposed speed limit then ultimately affects the amount of protein produced. Sometimes faster is better to express a high level of protein. Sometimes slower is better to limit the amount protein. ”
I have suggested that the melting temp of the two base pairs may be a significant selection difference. This may be another aspect of that.
UV PAPER http://www.daviddarling.info/encyclopedia/U/UV_origin_of_life.html
Catabolic and Anabolic evolved, but they did not blend.
2. This article suggests there is HGT, horizontal gene transfer in humans.
I suggest that this horizontal gene transfer is most likely in our gut bacteria.