Why is internal fertilization important for terrestrial life?

Internal fertilization is important for terrestrial life primarily because it allows the sperm to fertilize the egg within the female's body, eliminating the need for a liquid medium for the sperm to swim to the egg, which is typically needed in aquatic environments. In terrestrial habitats, the availability of water is limited, making it impractical for sperm to travel through a liquid medium. By being able to fertilize the egg internally, organisms maximize the chance of successful reproduction, as the sperm can reach the egg directly within the protective environment of the female's body.

This method also offers several advantages, such as protection of the developing embryo and a controlled environment for development, increasing the likelihood of survival for the offspring. Since external fertilization, which relies on water for sperm mobility, would not be as effective on land, internal fertilization represents a key evolutionary adaptation for reproduction in terrestrial animals.