ABSTRACT
Evolutionary
divergence has been characterized based on morphological and molecular features
using rationale based on Darwin’s theory of natural selection. However,
universal rules that govern genome evolution have not been identified. Here, a
simple, innovative approach has been developed to evaluate biological evolution
initiating the origin of life: whole genomes were divided into several
fragments, and then differences in normalized nucleotide content between
nucleotide pairs were compared. Intramolecular nucleotide differences in
complete mitochondrial genomes reflect evolutionary divergence. The values of
(G – C), (G – T), (G – A), (C – T), (C – A) and (T – A) reflect biological
evolution, and these values except for (G – C) and (T – A) change inversely to
positive from negative along biological evolution of bacterial genomes. More
highly evolved organisms, such as primates and birds, seem to have greater
levels of (C – T) in mitochondria. Based on nucleotide content structures, Monosiga brevicollis mitochondria may
be the most primitive extant ancestor of the species examined here. The two
normalized nucleotide contents are universally expressed by a linear regression
line, (X – Y)/(X + Y) = a(X – Y) + b, where X and Y are nucleotide contents and
(a) and (b) are constants. The value of (G + C), (G + A), (G + T), (C + A), (C
+ T) and (A + T) was ~0.5. Plotting (X – Y)/(X + Y) against X/Y showed a
logarithmic function (X – Y)/(X + Y) = a lnX/Y + b, where (a) and (b) are
constant. Nucleotide content changes are expressed by a definitive equation, (X
– Y) ≈ 0.25 ln(X/Y).