Reproduction is the biological process by which new individual organisms are produced.Reproduction is how living things make more living things. It is the process by which an organism produces offspring that carry its genetic material forward. Without it, every lineage would end with the death of its last member. Reproduction comes in two broad forms. In asexual reproduction, a single parent produces offspring that are genetically nearly identical to itself, as when a bacterium divides in two or a strawberry plant sends out a runner. In sexual reproduction, two parents each contribute a set of genes, and the offspring are genetically distinct from both. This distinction matters because it shapes how populations evolve. Asexual reproduction is fast and needs no partner, but it offers little genetic variation. Sexual reproduction is slower and costlier, yet it shuffles genes into new combinations each generation, which can help a population survive changing environments and resist parasites. Reproduction also explains many of the most striking behaviors and body forms in nature, from flowers that attract specific insects to the timing of when animals breed.
The distinction between sexual and asexual reproduction was recognized in the 18th century, and the role of cell division was clarified in the 19th century by researchers including Oscar Hertwig and Eduard Strasburger, who observed fertilization and meiosis under the microscope.
At the cellular level, reproduction depends on copying DNA and then dividing it into new cells. In asexual reproduction, a cell replicates its DNA and splits, passing a full set of genes to each daughter. In sexual reproduction, specialized cells undergo meiosis, a division that halves the chromosome number and shuffles genes through recombination. Two such cells, usually an egg and a sperm, fuse to restore the full set. The resulting cell divides repeatedly to build a new individual. Hormones and environmental cues often control when this happens, so that offspring arrive when conditions are favorable.
Understanding reproduction underpins agriculture, animal breeding, conservation programs, and assisted reproductive medicine such as in vitro fertilization.
Some species, like certain aphids and water fleas, switch between asexual and sexual reproduction depending on the season or the quality of their environment.