Ernst Mayr was the Grand Old Man (literally) of Evolutionary Theory.
He formulated the reproductive compatibility criteria for a species.
Ironically, this criteria is quite consistent with the Genesis language of each generation of animal from its own kind. It’s the perfect coincidence for a group like BioLogos!
If 2 strange animals cannot produce offspring, then they are not of the same kind. Boom.
Full stop! Drop the microphone!
None of this wishy-washy a kind is anything we want it to be stuff.
A horse and a donkey? Not the same kind! Mules are not fertile offspring.
A hyena and a wolf? Not the same kind!
A tiger and a lion? Well … woah there. They can produce fertile offspring. So the old phenotypical definitions might persist out of a sake of tradition - - but some of these felines are really more sub-species than fully differentiated species.
The biggest burden seems to be how to convince a YEC that once a group of animals are no longer reproductively unified to another population, that new group can eventually become anything, look like anything, without any permission from the “Religious Species” or “Religious Kind” Police !