Ring Species make me think

Every field has situations where definite "lines" get blurry - where constants are questioned and not always upheld. One I hadn't considered much was the definition of species. While this might not surprise some biologically-oriented people it was very interesting to me. It's difficult for me to describe so please read the Wikipedia article and BBC article about it.

To some degree this cuts under stark boundaries between different animals. It shows how all life is a complex tapestry of diverse and co-existing organisms.