Help in teaching 11-12 Year olds (RE (Religious Education) in the UK)

Hi Peg! I've been reading your argument about breeds and hybridization and enjoying it a lot. We know that pairs of what are called different species of animals can interbreed and produce hybrids. As, for example, lions and tigers; horses and donkeys; sheep and goats; finches and uhm, other finches? The normal creationist argument is that these aren't really different species or "kinds", they are just very different breeds of the same kind. That is, even though sheep and goats are very different varieties of creature, they do have a common descent, say from something on the ark for example. Whereas other things, like apes and men for example, are definitely not related, as proven by the fact that they cannot interbreed. That there is, as you have argued, an internal law or species barrier which prevents it, and which they cannot possibly breed past.So what I got to thinking was, a nice proof that this argument was wrong would be an animal A who could interbreed with animal B, and an animal C who could also interbreed with animal B, even though animal A could not possibly interbreed with animal C. Assuming evolution was right, we ought to have gobs of these kind of situations, right?