You are being taught a sort of bastardized version of the biological species concept. This was the dominant species concept through most of the 20th century but is now no longer as prevalent. I'll talk about some of the other species concepts in a bit, but first I'll explain why I say "bastardized".
Biological species are separated in nature. If you have two related but distinct populations of organisms which live in the same area and maintain their separate identities, they are two distinct species. This does not mean that the two are incapable of interbreeding and producing fertile offspring- often the species are quite interfertile but are separated by behavioral or temporal barriers. These two species may interbreed freely in captivity, where many of the barriers are broken down. They may even interbreed occasionally in nature, just not so frequently that the two species merge into one.
I'll use toads as an example. Here in my area there are two closely related toad species- Fowler's toad and the American toad. American toads breed early and have a long, musical trill. Fowler's toads breed later and have a short, nasal trill. However, their breeing seasons do overlap by a couple of weeks (incomplete temporal separation). Female American toads will seek out calling male American toads, not Fowler's toads, and vice versa. However, male toads will attempt to amplex anything vaguely toad-shaped that wanders into their field of view, so interspecific couplings are common (incomplete behavioral separation). Sometimes the female toad convinces the male that he has the wrong gal, but other times the two spawn and produce perfectly fertile hybrid offspring. These hybrids, while fit and healthy, are at a reproductive disadvantage because neither American nor Fowler's toads recognize them as suitable mates due to their mixed-up call and possibly smell (again, incomplete behavioral separation). So, the barriers separating these two populations are leaky, but still strong enough that they maintain their distinct identities throughout their large mutual range, and so qualify as distinct species.
The increasing use of multivariate statistics, biochemical information, phylogenetic classifications, and the difficulty of applying the biological species concept in many cases has led to the development of several new species concepts. The evolutionary species concepts identifies lineages with unique evolutionary trajectories. The genetic species concept identifies lineages by degree of genetic distinctiveness. The phylogenetic species concept is similar to the evolutionary species concept, but recognizes only 'splitting' of old species into two new species. None of these concepts is perfect, but they are used as models to constrain hypotheses of relationships among lineages.
Now adays leos originate from a large variety of both wild subspecies and species wich are so closely lookalikes former hobbists didnt realized that they were cross breding. When I wach wild forms of leos there are some that closely look like a snow, others that look like a high yellow,etc. Bearded dragons same thing, aparently the german giant was originated from a cross beetween viticeps and barbata, and now thouse genes are being injected into many bloodlines to make larger forms of many morphs, and so they are to a lesser degree hybrids too
