I’m probably abusing the term, but thread titles are only so long after all. What I mean is a world in which one of the prime engines of natural section–mutation–is stymied. Genes always replicate perfectly. Also, there is a sharp line between species; horses & donkeys, tigers & lions, chimps and bonobos absolutey cannot interbreed. (All races of humanity are part of the same species.) In short, all the crap Michael Behe spouts is true.
Here are a few more stipulations.
This world–call it Counter-Earth–was created ex nihilo by an omnipotent but not prescient–or even especially benevolent–deity, to see what would happen. This deity doesn’t care one way or another how much or little suffering occurs; he just wants to sit back with a really, really big tub of popcorn and watch. Pray all you want, but he ain’t picking up the phone. (But at least he’s not smiting anybody either.) This God also doesn’t care whether you worship him or any other deity or not. Counter-Earth orbits Sol in an orbit exactly opposite ours, kept stable and hidden from us with a miraculous cloaking device.
Counter-Earth began as an exact duplicate of our world as it was on at midnight on 23 October 4004 BC. Thsi includes copies of every person, animal, plant, geographic locale, and human artificat that existed at that time. There is one exception: Couch Potato God made sure every fossil, from apatasaur bones to microfossil, is entirely unrecognizable as such. The inhabitants of Counter-Earth are supplied with phony histories and memories matching those of the people they are based on.
How would you expect medicine to have developed on this world?