In this study we consider a mathematical model of a sexual population that
lives in a changing environment. We find that a low rate of environmental c
hange can produce a very large increase in genetic variability. This may he
lp to explain the high levels of heritability observed in many natural popu
lations. We also study asexuality and find that a modest rate of environmen
tal change can be very damaging to an asexual population, while leaving a s
exual population virtually unscathed. Furthermore, in a changing environmen
t, the advantages of sexuality over asexuality can be much greater than sug
gested by most previous studies. Our analysis applies in the case of very l
arge populations, where stochastic forces may be neglected.