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1. A new male trait arises, one that increases the mating success of the males, while having a detrimental effect on the females that respond to the new trait.

2. The fitness of the males with this trait rises. The fitness of the females responding to this trait goes down. Hence, males with this trait become more numerous in the population, while females responding to the trait become LESS numerous.

3. Some females evolve a trait that allows them to resist the males with the novel trait. The fitness of these new females rises, while the fitness of the males with the novel trait goes down. Hence, resistant females become more common, while males with the novel trait become less numerous.

4. Some males evolve a more extreme version of the trait, which overcomes the resistance of the females. Male fitness goes up, female fitness goes down.

5. The cycle continues.

The key to understanding the cycle is that male fitness and female fitness are opposed to each other, instead of being linked, as they are in runaway sexual selection.