Mammalian reproduction primarily occurs through sexual means, involving the fusion of male and female gametes. Male mammals produce sperm, while females produce eggs. Fertilization typically happens internally, leading to the development of an embryo within the female's body. Most mammals give birth to live young, a process known as viviparity. However, some, like monotremes (e.g., the platypus), lay eggs. Mammals also exhibit various reproductive strategies, including placental and marsupial development, which influence gestation periods and parental care.