  The natural evolution of life seems to proceed through steps characterized by
phases of relatively rapid changes, followed by longer, more stable periods. In
the light of the string-theory derived physical scenario proposed in [1], we
discuss how this behaviour can be related to a sequence of resonances of the
energy of natural sources of radiation and absorption energies of the DNA,
responsible for mutagenesis. In a scenario in which these energy scales run
independently as functions of the age of the Universe, the conditions for
evolutionary mutagenesis are satisfied only at discrete points of the time
axis, and for a short period, corresponding to the width of the resonance. We
consider in particular the evolution of the primates through subsequent steps
of increasing cranio-facial contraction, and the great Eras of life (Paleozoic,
Mesozoic, Cenozoic), showing that the transitions occur at the predicted times
of resonance.
