The standard neutral model and a selective sweep:
higher vertebrates do not have a high enough reproductive rate to support
rapid rates of beneficial evolution. It takes too many deaths to select for
new mutations.Kimura reasoned the majority of new mutations must be ‘
neutral’ The rate of neutral evolution could be much faster than positive
evolution, and would be limited only by the rate of DNA copying errors.
Since natural selection will not act on neutral traits, which do not affect
survival or reproduction, neutral evolution can proceed through random drift
without any inherent cost of selection.
A selective sweep is the reduction or elimination of variation among the
nucleotides in neighbouring DNA of a mutation as the result of recent and
strong positive natural selection.A selective sweep can occur when a new
mutation occurs that increases the fitness of the carrier relative to other
members of the population. Natural selection will favour individuals that
have a higher fitness and with time the newly mutated variant (allele) will
increase in frequency relative to other alleles. As its prevalence increases
, neutral and nearly neutral genetic variation linked to the new mutation
will also become more prevalent.
