 Additionally, sexual antagonistic co-evolution can be the cause of rapid evolution, as is thought to be the case in seminal proteins known as Acps in species of "Drosophila melanogaster".While Acps facilitate the mutually beneficial outcome of increased progeny production, several Acps have detrimental effects on female fitness as they are toxic and shorten her lifespan.This leads to antagonistic co-evolution, as the female must evolve in order to defend herself.