Ring species are an interesting case to consider, in which A and B can interbreed, and B and C can interbreed, but A and C cannot. Gene transfer between A and

Ring species are an interesting case to consider, in which A and B can interbreed, and B and C can interbreed, but A and C cannot. Gene transfer between A and C remains possible, but indirect. https://en.wikipedia.org/wiki/Ring_species https://en.wikipedia.org/wiki/Ring_species