I think the analogy to species is misleading. While there are interesting edge cases, the basic idea that there are different kinds of animals is really obvious

I think the analogy to species is misleading. While there are interesting edge cases, the basic idea that there are different kinds of animals is really obvious & clear: Sparrows don't try to mate with owls, seagulls, pigeons, let alone mice, earthworms & cockroaches. Instead with other sparrows, and produce more sparrows, which we can really confidently distinguish from owls, knowing just one of size/food/color/call would be enough. Nature is extremely clumpy here. Lots of points in the size/food/color/call space simply aren't occupied. Maybe a better analogy would be to the informally defined neighbourhoods which exist in many cities. Everyone knows there's a Little Italy and a China Town, and could point out the main street of each. But whether or not an apartment three blocks away is or isn't in that neighbourhood gets pretty fuzzy, and depends a lot on what the realtor thinks you are looking for.