The term 'species-crossing' refers to the process of hybridization, which is when two different species of plants or animals interbreed. Hybridization can occur naturally in the wild, or it can be artificially induced by humans. Hybridization can result in a variety of outcomes, including the creation of new species, the transfer of beneficial traits between species, and the development of new varieties of existing species. Hybridization can also be used to create new varieties of crops and livestock, as well as to improve the health and productivity of existing species.