Realistic models for ecological character displacement should incorpor
ate population genetics. In Slatkin's pioneering model (Slatkin 1980),
the genetics of the quantitative character determining the competitiv
e interactions are modeled by assuming that the character is normally
distributed in each generation. Only the mean and the variance of the
character distributions change over time. With symmetric ecological as
sumptions for the two competing species, and with normally distributed
resources that are equally used by both species, this model did not y
ield significant displacement. This has led to the belief that ecologi
cal asymmetries or constraints on resource use, e.g., by constraining
the phenotypic variances, are necessary for character displacement. I
argue that the reason for the negative result in Slatkin's original mo
del is that the genetics are modeled too rigidly. With a more flexible
genetic model, obtained by explicitly modeling many loci with additiv
e effects, character displacement occurs as a rule even for symmetric
ecological assumptions and without constraints on the phenotype distri
butions. The model can also be used in other contexts than competition
for resources. For example, character displacement in a host-parasite
system can lead to parasite specialization. The results suggest that
more detailed genetic models yield a finer resolution of the interacti
on between population genetics and ecological dynamics. Explicit genet
ics lead to more insights than the usual quantitative genetic assumpti
on of normal character distribution.