| He said that two organisms belonged to the same species if they are able to interbreed and produce fertile offspring. |
| It is part of a complex of closely related gull species that interbreed readily. |
| This helps explain why the success of hybrids is so variable and also why some species can, and others cannot, interbreed. |
| Because they are free to interbreed, the wild stock is of more or less mixed origin. |
| The biological definition of a species states that if two races interbreed they belong in the same species. |
| Organisms from distinct but closely related species may be able to interbreed. |
