> There is a reason biology tugs on ropes and lets reaction surfaces slide around instead.

And that reason is that it's very difficult to have a rolling joint or muscle because you can't get blood into it. It's largely fundamentally inaccessible to an organism that must grow itself. There are massive advantages that are unexplored by evolution.

Even further, gears are inherently asymmetric, meaning they are even harder to evolve. Nevertheless nature DOES use gears[1] when it can.

> You can shape the surfaces the way you want for the movement you need.

You can actually do the same with gears and screws: https://www.youtube.com/watch?v=100is1XpXcE

[1]: https://www.smithsonianmag.com/science-nature/this-insect-ha...