We've all heard how the wheel is one of man's greatest inventions, and there are many theories or ideas regarding how it was achieved.  Certainly it seems rather plausible that rolling logs probably played a role in this development.

However, the more I think about it, the more this invention seems to fall short.  It occurred to me that we were focusing on exactly the most obvious, yet wrong part of the wheel and missing the important bit.  A wheel is fundamentally useless, but the true stroke of human genius was the invention of the axle.

It was only through the axle that two important advancements occurred.  In one case, a long axle would serve to avoid rotating a load, so it could be held stable while the wheels rolled forward.  In the other case, such as a waterwheel, the axle served as a means to translate rotational energy into work by avoiding the natural forward movement of the wheel.

I can think of no instance where the wheel is capable of doing anything useful without the axle.  Therefore I think we need to give credit where credit is due and recognize that often the most important part of an invention may be the lesser "unsexy" part that is actually contributing the most to its utility.