Unless you can see Gods in the sky creating, smoting, having discussions with people through burning bushes and can replicate that process in the lab... See how this works?
You see evolution in progress all the time, all around you. Common lizards are the Eurasian ones I mentioned earlier that give live births in colder climes while still laying eggs where it's warmer. There's two species of skinks that do both as well, one in Australia apparently showing the beginnings of supplying nutrients, a possible precursor of placentas.
20% of reptiles give live births, not just your one anaconda.
There are three species of steamer ducks that can't fly at all. A fourth one, the flying steamer duck, can fly but doesn't do much of it. It can be found in the Falkland Islands (as well as the South American mainland) along with the Falkland steamer duck, which is flightless. They are genetically indistinguishable, so may very well be the same species (their populations are geographically separated). Regardless, flying steamers are evolving towards flightlessness like the other species already have.
In the 1980s, anole lizards were set loose on various tiny unpopulated islands in the Bahamas to study population pressures on limited areas. A decade later, differences in morphology were notable. On more windswept isles, they had developed shorter limbs, the easier to cling with lest they get blown out to sea. On less windier Islands, they had longer legs. This is in just a decade.
We see similar patterns with flying dragon lizards in the Philippines, only extending back far longer. Those on windier islands had shorter legs, and shorter gliding ribs, while those less windier places had longer legs and longer ribs.