Females have more control over mating outcomes than previously thought. Research shows that females can accept a male for copulation but reject him as a father through cryptic mechanisms. This selectivity by females is common across various species. Female behavior, morphology, and physiology play a significant role in post-copulatory competition between males for paternity. The study covers examples from a wide range of organisms, highlighting the influence of female choice on male success in reproduction. Cryptic female choice links sexual selection theory with reproductive physiology, showing how male seminal products affect female reproductive processes.