The evolution of host susceptibility or resistance to parasites has im
portant consequences for the evolution of parasite virulence, host sex
ual selection, population dynamics of both host and parasite populatio
ns, and programs of biological control. The general observation of a f
raction of individuals within a population that is not parasitized, an
d/or the variability in parasite intensity among hosts, may reflect se
veral phenomena acting at different levels of ecological organization.
Yet, host-parasite coevolution requires host susceptibility and paras
ite virulence to be genetically variable. In spite of evolutionary and
epidemiological implications of genetic heterogeneities in host-paras
ite systems, evidence concerning natural populations is still scarce,
Here, we wish to emphasize why we need a better knowledge of the genet
ics of host-parasite interaction in natural populations and to review
the evidence concerning the heritability of host susceptibility or res
istance to parasites in natural populations of animals.