Which reproductive method is universal among mammals?

Fragmentation, Budding, and Regeneration are methods of asexual reproduction, typically found in simpler organisms like plants, fungi, and some invertebrates. Mammals reproduce sexually, so these methods are not applicable.

External fertilization is a method where fertilization occurs outside the body, commonly seen in aquatic animals like fish and amphibians. Mammals, however, have internal fertilization, where the sperm fertilizes the egg inside the female's body.