  We discovered a dynamic phase transition induced by sexual reproduction. The
dynamics is a pure Darwinian rule with both fundamental ingredients to drive
evolution: 1) random mutations and crossings which act in the sense of
increasing the entropy (or diversity); and 2) selection which acts in the
opposite sense by limiting the entropy explosion. Selection wins this
competition if mutations performed at birth are few enough. By slowly
increasing the average number m of mutations, however, the population suddenly
undergoes a mutational degradation precisely at a transition point mc. Above
this point, the "bad" alleles spread over the genetic pool of the population,
overcoming the selection pressure. Individuals become selectively alike, and
evolution stops. Only below this point, m < mc, evolutionary life is possible.
  The finite-size-scaling behaviour of this transition is exhibited for large
enough "chromosome" lengths L. One important and surprising observation is the
L-independence of the transition curves, for large L. They are also independent
on the population size. Another is that mc is near unity, i.e. life cannot be
stable with much more than one mutation per diploid genome, independent of the
chromosome length, in agreement with reality. One possible consequence is that
an eventual evolutionary jump towards larger L enabling the storage of more
genetic information would demand an improved DNA copying machinery in order to
keep the same total number of mutations per offspring.
