of onions planted in the United States were F1 hybrids. Beans and peas are not commercially hybridized because they are automatic pollinators, and hand pollination is prohibitively expensive. F2 hybrids F2 hybrids, the result of self or cross-pollination of F1s, lack the consistency of F1s, though they may retain some desirable traits and can be produced more cheaply because hand pollination or other interventions are not required. Some seed companies offer F2 seed at less cost, particularly in bedding plants, where consistency is less critical. In animals F1 crosses in animals can be between two inbred lines or between two closely related species or subspecies. In fish such as cichlids, the term F1 cross is used for crosses between two different wild-caught individuals that are assumed to be from different genetic lines. Mules are F1 hybrids between horses (mares) and donkeys (jacks); the opposite sex cross results in hinnies. However, such offspring are almost always sterile. Today, certain domesticated–wild hybrid breeds, such as the Bengal cat and the Savannah cat, are classified by their filial generation number. An F1 hybrid Savannah cat is the result of reproduction between an African Serval cat and a domestic cat. As explained in the International Journal of Fauna and Biological Studies, there are four reasons for species hybridizations: Small population size Habitat fragmentation and species introduction Anthropogenic hybridization Visual, chemical, and acoustic interferences Small population size can be caused by inadequate or obliterated natural habitats that lead to species escaping to other habitats and as a result, this may lead to lesser mate availability and can cause breeding between distinct species. Habitat fragmentation and species introduction can be man-made or caused by mother nature such as deforestation, desertification, eutrophication, urbanization, water oil extraction causing changes in the ecosystem that leads to animal migration or evading new surroundings. Third, is anthropogenic hybridization, which is "artificial or human-led hybridization" is supported for researchers to study "reproductive compatibility between species". Lastly, visual, chemical, and acoustic interferences cues are what causes species to signal sexual cues by differentiating between the same and opposite-sex leading to hybridization. Advantages Homogeneity and predictability: The genes of an individual plant or animal F1 offspring of homozygous pure lines display limited variation, making their phenotype uniform, so attractive for mechanical operations and easing fine population management. Once the characteristics of the cross are known, repeating this cross yields the same result. Higher performance: