If tigers/lions and grizzly/polar bears can reproduce, are they the same species of cat/bear?

Many textbooks will tell you that two varieties are considered the same species if they can interbred and get fertile offspring. According to this definition, lions and tigers should be considered the same species if the tions (ligers?) are fertile. But even if this is the case, few zoologists would seriously argue that they should be considered the same species. Because they have been assigned different systematic (Latin) names which are used in thousands of books and articles. So it would create a lot of confusion if we suddenly had to consider them the same species.





Strictly, the interbreeding criterion is not a definition. Because when a new variety is found, zoologists want to decide quickly if it is a new species or not. It will not usually be feasible to carry out breeding experiments.

If tigers/lions and grizzly/polar bears can reproduce, are they the same species of cat/bear?
The offspring would have to be fertile, and litter sizes would have to be comparable (that is, you can't have large numbers of offspring dying in utero).





The thing about the term species, it's a term that humans artificially use to help us classify things. It doesn't have a clearly defined biological basis. The theory of evolution tells us that every individual organism, and every population of organisms is unique, and therefore, we have to expect that we will not be able to categorize every single possible interaction of closely related organsims perfectly well with one simple rule.