Here are four ways in which honest signals of good genes might be enforced:
- Another hypothesis for female mate choice is that females should mate with
males which are immunologically dissimilar. This would give their offspring
high immune diversity and, in theory, make their offspring more disease resistant.
This can actually happen, as odors may correlate with immune
system diversity.
- Finally, effects of the environment on developmental variation produces
assymetry in body form in animals. More highly symmetrical animals may have
better genes for coping with environmental variation. So, if females choose
for symmetry, they may be using an honest signal of "good genes".
The use of this type of symmetry, called fluctuating assymetry,
is a controversial area of research in animal behavior.
- Another way in which animals may be unable to avoid producing honest signals
of their fitness is by their ability to cope with parasites. Plumage color
in some birds may be brightest in individuals with lower parasite loads, and
dullest in highly parasitized birds. If "good genes" are responsible
for lower parasite loads, then bright plumage color
reflects good genes.
- If the sexually selected trait is actually a handicap for the animal carrying
it--there is a price in energy or vulnerability to predation, for example--then
the sexually selected trait, such as huge antlers, becomes an honest advertisement
of the male's ability to carry the handicap.