Grrl Power IV: Constantly Expanded Universe

[halfeye]

In order to get genetically compatible and physically indistinguishable humans out of ~4 billion of years of evolution on two different planets, you'd need to interfere for about 3.999 billion of those years on one or both planets.

That's always been true, and science fiction authors have always ignored it.

People are just stupid that way.

With any sort of theatre, TV or movies there's always the extra problem/excuse that actors are always human, but book authors very often make their aliens human even when there's no obvious chance of a film adaptation.