They were based on the kind of biology that is currently taught in schools, most of which is about thirty years out of date. Like almost everything in school science, because it takes at least that long for ideas to ‘trickle down’ from the research frontiers to the classroom. Most ‘modern mathematics’ is at least 150 years old, so thirty-year-old biology is pretty good. But it’s not what you should base your thinking on when discussing cutting-edge science.
Terry Pratchett, Ian Stewart, and Jack Cohen, The Science of Discworld III: Darwin’s Watch