 Although most species on the planet reproduce sexually, why do some species still reproduce asexually? Why is it evolutionarily beneficial for some species to require two parents to produce offspring and others only one? Let's explore why different forms of reproduction exist and what makes each one beneficial in specific circumstances. The two types of reproduction are asexual and sexual. Sexual reproduction is when an organism makes a genetically identical clone of itself. Most of the simplest life forms, such as bacteria, reproduce in this manner. Sexual reproduction is much more complex and involves two members of a species coming together to produce genetically distinct offspring. Most eukaryotic multicellular organisms, such as humans, birds and insects, undergo sexual reproduction. The biggest advantage of sexual reproduction is that offspring are genetically distinct from their parent and siblings. This allows a species to evolve since natural selection will favor the offspring carrying genes that improve their survival in diverse environmental conditions. For example, humans who carry two abnormal copies of the hemoglobin gene develop sickle cell anemia, a devastating disease that results in abnormally low levels of oxygen in the blood. Individuals who have only one copy of the abnormal gene have a much less severe form of the disease. Interestingly, heterozygous individuals are much less prone to infection by malaria, making them more likely to survive and have high reproductive success in malaria endemic areas. This example shows how sexual reproduction can produce offspring who are genetically distinct from their parents and are better suited to survive under certain environmental conditions. We have been talking about genetic diversity, but how does sexual reproduction generate this diversity in the first place? During meiosis, which produces the sperm and the egg needed for sexual reproduction, there are two key steps that produce genetic diversity. First is recombination between homologous chromosomes. Recombination mixes maternal and paternal alleles and results in novel gene combinations on each chromosome in each generation. The second is the independent assortment of chromosomes, which generates unique combinations of chromosomes in each gamete. During fertilization, one genetically unique sperm and one genetically unique egg randomly combine to form an offspring that is genetically distinct from its parent. While genetic diversity arising from sexual reproduction has been critical for the survival of many species, mating is an energy consuming, slow and risky process. To improve the chance of selecting the best partner and therefore the best alleles, some species have evolved highly sophisticated courtship behaviors. Male peacocks, for example, grow long iridescent tail feathers and perform in a labored dance to attract a mate. But this process requires energy and can attract predators. In addition, the generation of gametes for sexual reproduction and the subsequent gestation and incubation take time and energy. For example, emperor penguins must sit on their eggs for over two months and elephants can be pregnant for almost two years. While asexual reproduction does not produce genetically distinct offspring, it has important advantages that allow for species survival. One, it is energy efficient and does not require attracting a mate. Two, it is usually fast. Some bacteria can reproduce in as little as 20 minutes. And three, it produces offspring that are genetically identical, an advantage in stable environmental conditions. For example, bacteria that carry an empecyline antibiotic resistance gene will continue to grow in patients prescribed this antibiotic. Conversely, because asexual reproduction results in genetic clones, these bacteria would all die if the patient was treated with a different antibiotic. Rare, random mutations in the genome do allow asexually reproducing organisms to evolve diversity. However, this is a slow process and there is no mechanism to separate harmful and beneficial mutations for propagation to future generations. Both sexual and asexual reproduction provide important methods for species survival and adaptation, allowing the millions of species on Earth today to evolve and survive in their current forms. This video has been provided to you by Eureka Science and iBiology, bringing the world's best biology to you.