One of the most important arguments for evolution–arguably more important than the fossil record–is the patters of similarities we see among modern organisms. Since before Darwin, biologists have realized that all modern organisms fall naturally into a series of small groups nested into larger groups, and there’s clearly one way of grouping together that is clearly superior to all the countless others. This makes sense if common descent is true: the smaller groups (genera) are the ones that share a relatively recent most recent common ancestor, the larger groups (family, order, class) are ones whose most recent common ancestor is a bit farther back, and the largest groups (from phylum to all of life) are the ones that only have a common ancestor when you go really far back.

We only see this kind of pattern a few other places in the world. Even if you didn’t know that Spanish, French, and Italian all come from Latin, it would be obvious that in some sense they go together. And just as genera fit into larger taxons, the romance languages are part of the Indo-European family, whose existence linguists have inferred from careful comparing of the romance languages to other world languages. But the pattern definitely doesn’t appear in most human artifacts, because unlike languages and species, artifacts aren’t produced by a common-descent process: if a car manufacturer comes up with an improved car engine, the improvement can be applied to all lines of cars everywhere, which doesn’t happen in a common descent system.

In response to this argument, many creationists insist that the explanation for the pattern of similarities we see today is not common descent, but common design. This explanation could work–if they thought that when God was designing life on Earth, he delegated all the work to angels, and the angels were divided into a department of animals, department of plants, etc. then smaller departments for every single grouping of organisms biologists have discovered–and only then if the angles had very peculiar rules for sharing innovations between each other. This isn’t actually what creationists believe, is it?