The ability to breed successfully, producing fertile offspring is an essential definition of species. A finch will always produce a finch but over generations, one population of finch may no longer successfully breed with another. Horses and burros are close relatives but different species with the mule offspring only very rarely being fertile.
BTW there are several separate “rat” species.
You win - Man made global warming made the fleas evolve. You and the good professor should report to Stockholm to collect your Nobel prizes.
:-)
BTW - horses and burrows have different numbers of chromosomes, a *huge* genetic difference.
but -
You win - Man made global warming made the fleas evolve. You and the good professor should report to Stockholm to collect your Nobel prizes.
:-)