I'm tempted to point out that reptiles are so distinct from either mammals or insects that they wouldn't be a natural stepping stone. But some of my esteemed co

I'm tempted to point out that reptiles are so distinct from either mammals or insects that they wouldn't be a natural stepping stone. But some of my esteemed colleagues advocate jumping from zebrafish to mouse, and I just realized they're probably thinking along similar lines: why try to figure out insects along the way from fish to mammals? Personally, though, I'm limiting my scope to the worm (at least for now!). The particular path which is best to take beyond that is much less clear.