[doomrobo]

One example I particularly like is why there aren't animals that roll as their primary method of transportation. The steps in between walking and perfect roundness are so disadvantageous that mutations in that direction would probably be the death of that individual (imagine a square armadillo). If an animal was genetically engineered to be able to roll without all the steps I'm between, it might make them even more fit than their non-mutated cousins.

[Someone]

https://en.m.wikipedia.org/wiki/Category:Rolling_animals

Video at https://www.youtube.com/watch?v=HmLS2WXZQxU.

I think you won't find animals that use rolling as their primary method. Problems is that for feet, you need a patch of relatively flat surface every footstep. For wheels, you need a continuous stretch, or you need a design that can withstand impacts. Small animals have an advantage there, as gravity isn't as harsh on them as on larger animals.

And of course, there's Pedalternorotandomovens Centroculatus Articulosus (https://en.m.wikipedia.org/wiki/Curl-up)

[doomrobo]

Very interesting. I kinda figured my explanation wasn't that accurate, but I think it conveyed the point pretty well that sometimes we can't get to new optimal states because every path to that state is worse than the current optimal state.