copulation

Copulation is the act by which two individuals unite to transfer male gametes to the female reproductive tract, enabling sexual reproduction. In many animals, the act involves the male's intromittent organ becoming inserted into the female, culminating in the transfer of sperm. In other species, sperm transfer occurs through specialized structures or contact without insertion, and fertilization may be internal or external.

Internal fertilization is common in mammals, birds, and many reptiles, where copulation is typically followed by fertilization inside the female body. External fertilization occurs in many fishes and amphibians, where gametes are released into the environment, often in large numbers, and fertilization happens outside the body. Some invertebrates use complex mating mechanisms, including spermatophores or production of a sperm transfer appendage.

Copulation is influenced by mating systems and sexual selection, with behaviors such as courtship, aggression, and competition shaping duration and frequency. Anatomy, pheromones, and neural mechanisms regulate readiness, arousal, and reproduction.

In humans, the term is often used to describe sexual intercourse, though reproduction can also occur through assisted methods. Copulatory behavior varies widely across species in duration, frequency, and ritualization, reflecting diverse ecological pressures and life histories. It remains a central topic in studies of reproductive biology, ethology, and evolution.