Sperm Wars

For all she knew, her son might have produced children with some of these other women.

For all she knew, her son might have produced children with some of these other women. He might even have tricked other men in the same way that his genetic father had tricked the man who had just died. Evolutionary pressures. Human sexual behavior and psychology have been shaped by millions of years of evolution to maximize reproductive success. This doesn't just mean having as many children as possible, but optimizing for quantity and quality of offspring that will survive to reproduce themselves. Unconscious motivations. Much of human sexual behavior is driven by unconscious evolutionary impulses rather than conscious decision-making. People often act in ways that enhance their reproductive success without realizing why they are motivated to do so. For example: Men are attracted to signs of youth and fertility in women Women are attracted to signs of resources and good genes in men People experience jealousy to guard against infidelity Adolescents are driven to sexual experimentation to gain skills Cultural variability. While the underlying evolutionary drives are universal, how they manifest varies across cultures. Different societies have different norms around: Courtship rituals Marriage customs Acceptable sexual practices Gender roles

As soon as a killer from either man first encounters a sperm from the rival, it is alerted that war has begun. Sperm warfare. When a woman has sex with multiple men in a short time period, sperm from those men compete within her reproductive tract to fertilize her egg. This competition has shaped male anatomy and sexual behavior: Penis shape evolved to displace rival sperm Men produce more sperm when they suspect partner infidelity Men experience sexual arousal from seeing other couples mate Female adaptation. Women's bodies have also adapted to influence the outcome of sperm competition: Cervical filter can impede or assist sperm passage Orgasms can enhance or inhibit sperm retention Unconscious ovulation in response to new partners Strategic behavior. Both men and women engage in behaviors to manipulate the sperm competition process in their favor: Mate guarding by men to prevent rival insemination Women timing intercourse with different partners strategically Use of oral sex to detect rival sperm

As she kissed, their fingers stroked and probed each other's wet vaginal lips, then massaged each other's clitoris. Each knew exactly what to do. Orgasm function. Female orgasms are not just for pleasure, but serve important evolutionary functions related to conception: Upsuck effect pulls sperm further into reproductive tract Cervical dipping exposes sperm to more acidic environment Contractions can expel sperm from undesirable partners Strategic timing. When women have orgasms relative to their partner's ejaculation impacts sperm retention: Orgasm before male ejaculation strengthens…