Alas no hard and fast rule that I'm aware of that fits all cases. It's just a level of difference in which somebody goes, yip let's draw a line here and from a

Alas no hard and fast rule that I'm aware of that fits all cases. It's just a level of difference in which somebody goes, yip let's draw a line here and from anything going forwards is a new species. Heck, it certainly isn't defined by having interchangeable blood as we all know that don't work with humans.