[oxzplvsg] Evolution of duck vaginas

Ducks evolve corkscrew vaginas only if mate selection by females is accurate.  In order to evolve more corkscrew, female ducks with less corkscrew -- on whom forced copulation lead to fertilization of their eggs -- must be less likely to produce successful offspring.  Meanwhile, ducks with more corkscrew produce offspring from a selected mate instead of a forced copulation.  Those offspring must be more successful.  Exactly what does the female evaluate in a male that allows the female to accurately predict whether or not their ducklings will die before maturity?  What other mechanisms, if any, are going on?

Accuracy could be low, but it must be better than random.

On one hand, there are so many ways that mate selection might be worse than random.  Beautiful male plumage might be more likely to be seen by predators.  The environment might change such that a desirable feature becomes disadvantageous.  There may evolve male features to fool the females' mate selection criteria.

On the other hand, it is obvious that mate selection must be accurate, or else they wouldn't do it.  The drake thinks to himself, "She doesn't want to have sex with me because I am an inferior being."  And he is correct.

In what other species is mate selection provably accurate?

Not only must mate selection be accurate, but it must remain persistently accurate generation after generation, even after one advantageous selected-for trait has come to dominate the population.