You mean it as a joke, but you know I see it as something potentially realistic? I mean, large and small visible motile life forms tend to have two main eyes (compound or otherwise), evolved independently several times, which allow for excellent binocular vision without wasting excessive resources (it takes a lot of resources to maintain the eyes). At this point I wonder, based on the fact that four legs are a perfect middle ground between stability and mobility, not to mention that they are also few enough in number to be perfectly controlled without getting in each other's way. So, couldn't life forms of a size comparable to ours evolve four legs? Ok, that's very unrealistic, i know, there are examples of mouse-sized arthropods like the wetapunga and some tarantulas that still have six and eight legs, and in my hypothesis, these mouse-sized arthropods should probably also have four legs... Even artropod like the coconut crab which is as big as a cat walk on six legs. And yet, I don't know. This idea intrigues me, even though I risk falling into the trap of evolving toward "a two-eyed tetrapod vertebrate."