Meiosis may have evolved gradually within the eukaryotes with the earliest
forms having a one-step meiosis. It has been speculated that the putative t
ransition from a one-step meiosis without recombination to one with recombi
nation may have been stimulated by the invasion of Killer alleles. These im
aginary selfish elements are considered to act prior to recombination. They
prime for destruction (which occurs after cell division) the half of the c
ell on the opposite side of the meiotic spindle. Likewise the transition fr
om one-step to two-step meiosis might have been stimulated by a subtly diff
erent sort of imaginary distorter allele, a SisterKiller. These are propose
d to act after recombination. It has yet to be established that the presenc
e of such distorter alleles could induce the transitions in question. To in
vestigate these issues we have analysed the dynamics of a modifier (1) of r
ecombination and (2) of the number of steps of meiosis, as they enter a pop
ulation with one-step meiosis. For the modifier of recombination, we find t
hat invasion conditions are very broad and that persistence of Killer and m
odifier is likely through most parameter space, even when the recombination
rate is low. However, if we allow a Killer element to mutate into one that
is self-tolerant, the modifier and the nonself-tolerant alleles are typica
lly both lost from the population. The modifier of the number of steps can
invade if the SisterKiller acts at meiosis II. However, a SisterKiller acti
ng at meiosis I, far from promoting the modifier's spread, actually impedes
it. In the former case the invasion is easiest if there is no recombinatio
n. The SisterKiller hypothesis therefore fails to provide a reasonable acco
unt of the evolution of two-step meiosis with recombination. As before, the
evolution of self-tolerance on the part of the selfish element destroys th
e process. We conclude that the conditions under which SisterKillers promot
e the evolution of two-step meiosis are very much more limited than origina
lly considered. We also conclude that there is no universal agreement betwe
en ESS and modifier analyses of the same transitions.