symbasis

from The Century Dictionary.

• noun The type of deseent found in large groups of freely interbreeding organisms, such as natural species.
• noun The normal biologic condition of free interbreeding among organisms of the same specific or subspecific group: distinguished on one side from too wide cross-breeding, and on the other from too narrow inbreeding.
• noun Generation by the union of the sexual products of two individuals; cross-fertilization as distinguished from self-fertilization.