Sorry I forgot you do not use common sense, A king will not breed an ant either, but surely there are much closer things that are not the same. Like gopher/king crosses. You do understand, they have been seen in captivity and nature. Or various rattlesnake crosses(many types) in nature.
Hybrids are actually fairly common in nature. But they do not "fit" so most do not survive. Now consider, if 95% of normal offspring do not survive, and they are selected for, then what percentage hybrids would survive. The answer is most likely very very low. I would say zero, but unfortunately we have a nearby population that relatively commonly contains hybrids(mohave/diamondbacks)
You must consider, behavior plays a very important part in this. In fact, its more important then physical rules. We know, so many species can be crossed with other species or even genera and produce viable offspring. So, physically its possible. Yet its rare in nature. So what prevents it? As my partner said in another post, elementery my dear watson, its behavior, as in behavioral barriers. The problem is, these are breachable. They don't always work or are not always present.
For instance, we have two types of very similar lizards, a Clarks spiny and a Magisters spiny, They are the same size, shape, etc etc. Yet are different, they occur in the same habitats or different habitats. They occur in areas away from eachother, and also overlap. Yet they do not normally cross when they overlap, in nature. But if you take one individual from a population that is not exposed to the other similar type(no need to develop barriers) and expose it to an individual of the other species, thats from a population that is not exposed to that species, again no need to develop preventive barriers, then sir, all bets are off.
But then if it serves you that an ant cannot breed with a polar bear, then perfect, after all, if it serves you, then who cares. Please don't get mad, all I am doing is taking larger extreme then you. You do understand, theres plenty of cases that are not so extreme. FR