  The post-genomic era has brought opportunities to bridge traditionally
separate fields of early history of life and brought new insight into origin
and evolution of biodiversity. According to distributions of codons in genome
sequences, I found a relationship between the genetic code and the tree of
life. This remote and profound relationship involves the origin and evolution
of the genetic code and the diversification and expansion of genomes. Here, a
prebiotic picture of the triplex nucleic acid evolution is proposed to explain
the origin of the genetic code, where the transition from disorder to order in
the origin of life might be due to the increasing stabilities of triplex base
pairs. The codon degeneracy can be obtained in detail based on the coevolution
of the genetic code with amino acids, or equivalently, the coevolution of tRNAs
with aaRSs. This theory is based on experimental data such as the stability of
triplex base pairs and the statistical features of genomic codon distributions.
Several experimentally testable proposals have been developed. This study
should be regarded as an exploratory attempt to reveal the early evolution of
life based on sequence information in a statistical manner.
