The primary condition for speciation is reproductive isolation. That is the main 'definition' of a species, that they do not reproduce with other different species. The horse has a genetic link to other horse descendants. These all indicate a narrowing of the genetic material.. a 'devolution' if you will. A donkey came from the same parent species as the horse & zebra, but they are not able to reproduce viable offspring.. they CAN reproduce, but the progeny is sterile.. like the mule. But instead of this indicating an EXPANSION of trait availability, the facts are the exact opposite. It was a narrowing of the gene pool that isolated the horse, donkey, & zebra. All of those animals descended from the same parent species.. we can trace that. But instead of opening up new traits of variability, they lost them. The zebra traits don't come up in donkeys anymore. And new 'species' are not being produced. What we see with the horse genetic line is a branching into a dead end. The variability is lost, as the progeny do not have the variety to pick from in their parent's dna.
You can explain the tree branches somewhat with evolution. But you still don't have the mechanism that enables the leaps between the family/genus/species. As science, the 'amoeba to man' theory is full of holes, yet it is taught as though it is proven fact. The observable, repeatable FACTS are that breeding & natural selection NARROW the genetic availability, until the species reaches equilibrium & loses variability. That is why a brown rabbit is seldom (never?) born in the snowshoe rabbit species anymore. It is why chihuahuas do not produce an occasional wolf. That variability is lost, & the breed is limited to the narrow band of variability. The very science of breeding is contrary to the premise of evolution: that new genetic material is constantly being produced & increasing the complexity & variability within a species. We observe the exact opposite. We repeat the exact opposite.
Even if some 'new' trait is discovered while breeding, now we know it was there.. hiding in the massive dna strands. It might take thousands or millions of generations for it to pop up, but when it does, this did not mean a new trait made itself, just that the hidden gene took a while to hit the jackpot. It is like pulling on a slot machine in vegas.. if you pull it enough times, eventually the sequence will come up that hits the combination you want. That is all breeding & natural selection is, except they get to narrow the variability & reduce the 'losing' combinations. Slot machines don't let you do that.
Why do species go extinct? Because they lose the variability needed to adapt to the changing environment. They don't create genes to survive if conditions change. If there is some variability already in them that increases their survival rate, then that trait will become more prominent. But if they don't have that trait, they die off. That is observable reality, not that species create new genetic information to adapt.
Modern genetics is one of the biggest enemies of the old 'theory' of evolution. Eventually, the facts will overwhelm the beliefs, & the scientific establishment will come up with a new pop theory of origins. But they still are working this one for now. It is everywhere.. tv, national parks, museums, schools.. anywhere science is mentioned, evolution is tacked on, to prop it up as a belief. But real science does not support the theory. All of reality screams, 'NO!'. But since when have humans cared about reality? :)