Since members of different species cannot successfully interbreed, it’s in every organism’s best genetic interest to mate only with members of the same species. So you’d expect mechanisms to evolve that allow animals to recognize members of their own species. And, indeed, that is the case.
If one sex invests more in reproduction than does the other, as is frequently the case, the sex that invests more in reproduction has more to lose by choosing the wrong partner. Accordingly, you’d expect selection for more “choosy” behavior when it comes to selecting a mate in the sex that has more to lose. Usually, the female invests more in reproduction than does the male, and indeed, females, on average, seem to be much more careful than males when selecting potential mates.
So prevalent is this that it’s frequently referred to as the “female choice model.”
If selection favors “choosy” behavior in one sex, it’s in the best genetic interest of members of the opposite sex to somehow advertise their suitability as mates. So it’s most-often males who have evolved means of indicating the species to which they belong –
and their suitability as mates.
Male and female Northern Cardinals (Cardinalis cardinalis
): In many songbird species, males are
much more brightly-colored than are females. As a rule, the more brightly-colored the male,
the healthier he is and the fewer parasites he has. When given a choice, females generally
prefer more brightly-colored males as mates. Their bright colors allow males to demonstrate
their fitness and, therefore, their suitability as potential mates.
Female Choice
Linear Mode
