The idea of a world with life as we know it that doesn’t evolve is not plausible. The fact that all life on Earth appears to be descended from a common ancestor is a fact that we know about how life evolved, not a part of the definition of the process itself. Even if some god created a world full of already-complex life, it would still then, given that mutations exist, take a specific effort on the creator’s part to prevent evolution by natural selection from occurring after that.
Of course evolution denialists think they have a trump card there. They say that ‘micro-evolution’ is real enough but that ‘macro-evolution’ has not been proven (quotes because cdesign proponentists have been known to use those terms in contexts where no one else ever would)…but that’s a mere assertion with nothing to back it up and not even a suggestion as to what sort of mechanism there even might be to prevent ‘micro-evolution’ from acting cumulatively in such a way that it would become ‘macro-evolution’. (And no, pretending that the Earth isn’t old enough for ‘macro-evolution’ to have happened is not a real explanation; it also has all sorts of other problems that I’ll describe in a future post.)
If the difference between ‘micro’ and ‘macro’ is whether or not a new species evolves, then let’s start our examples of how one could become the other with the most diverse animal species on Earth; no, not humans. Dogs. Thanks to intentional selective breeding by humans, they have evolved faster than any other mammal over the last 10,000 years, and in more different directions. Some of them still look almost the same as wolves, while others are very different. Some have very long snouts, others very short. Some are shaggy, some are short-haired. And most relevantly, some are huge and some are tiny. The size difference makes it impossible for a great dane and a chihuahua to breed. (Unlike Pokemon, where a whale can breed with a cat…or even with an acorn.) They’re considered the same species now because there’s a continuum of dog sizes, but if medium-sized dogs became extinct, small dogs and large dogs would immediately become different species by the common definition.
But it could also happen just by keeping them separated. They’re already pretty distinct; if all dog breeds were only pure-bred for a thousand years (which might be considered artifically induced sympatric speciation), the odds are that the ones that changed the most during that time would be incapable of breeding with any other breed. (And yes, it’s annoying that the same word means two different things.)
And breeding of domesticated foxes has shown that in canines, behavioral traits like tameness are directly linked to specific physical traits, which explains why dogs breeds look so different. (The practice of breeding them specifically to look unique didn’t start until modern times.)
This is the most common way that speciation occurs; two groups of what was the same species are separated and evolve differently, and eventually they would be incapable of reproducing even if they did try to. This is why there are over a million species of beetle. (Seriously, I want to know how creationists explain the creator’s beetle fetish.)
Of course, one area in which evolution is both obvious and directly impacts everyday life would be the evolution of infectious bacteria. Anyone who really has faith in the non-existence of evolution is welcome to limit themselves to first-generation antibiotics.