There have been several discussions about mechs, and the general consensus is - whilst cool, they're not actually a very good design.

[Plausible Reasons for usage of Combat Mecha](https://worldbuilding.stackexchange.com/questions/10320/plausible-reasons-for-usage-of-combat-mecha)

What I was wondering though - how much of this discussion applies to organics?

First off: What ways - if any - could wheels have been evolved? As far as I'm aware there are no examples of rotary motion in a living creature - whilst we can 'windmill' our arms, that's multiple joints moving to create that effect.

Is there any evolutionary branch that *might* have done this?

I mean, it's only relatively recently that we've even got circular impulse - trains and the like are 'driven' via a linear piston, as are combustion engines. (Unpowered of course - wheels are pulled or pushed by things on legs anyway)

Rotary engines and electric motors are close, but they're still a linear impulse around a circular axis. So it sounds like the evolutionary key here is a 360-degree pivot because then you can translate linear to circular motion. It's also something that doesn't appear to have ever evolved. 

For the sake of argument - if some fluke caused 'wheels' to evolve somehow - which branch would likely have won, evolutionary speaking? Do the same square/cube laws that make the mech worse than the tank also apply to evolved species, or is the efficiency of rotary motion a major positive factor?