Reproduction ensures that a species does not become extinct. Humans have sex and reproduce so that we continue to exist on the planet.
However, research shows that the aim of having sex is NOT just to procreate. Various species have sex for reasons other than reproduction.
Some reasons that humans have sex (solo or partnered) are:
- stress relief,
- physical desire,
- thrill and desire for new experiences,
- emotional reasons including love (and a way to express love), and
- boosting self-esteem