Its definitely a wheel. There is the whole history of it and how it moved the civilization forward at the Smithsonian. Amazing exhibit.

Backscratcher

The use of fire. Or how about horticulture? Or maybe: shoes.

Many ancient civilisations flourished without ever inventing the wheel, or glass but none flourished without the invention of the lever or the sharp edged blade.

@darren316

Yes....wheels win the Pre-historic invention "device" or "tool"

But then there's clear glass windows.

Hinges and handles are up there, IMHO.

As are plows....which gave birth to agriculture...which gave birth to our first population boom.

But these "tools" and "inventions" are now thousands of years old.

About a thousand years ago we went from devices to processes that are the "winners"...

Kudos to
-mathematics (this goes back 2 or 3 thousand years...depending on the formulas and their uses)
Then art....statuary, painting...less than 2000 years ago

Then, less than 1000 y.a.

-astronomy (the lens - and the microscope and telescope) - Thanks to Copernicus, Galileo, Leeuwenhoek - and let's not forget eyeglasses..(thanks, Ben Franklin!).

And only a few hundred years ago
-evolution
-germ theory
-medicine, and public sanitation

Louis Pasteur and many others....

Imagine if we didn't solve the "Bubonic" plague? And yes...that's where the term Bubu comes from!

I think that greatest invention in the history of mankind has got to arithmetic/ mathematics. Without mathematics the world as we know it would not exist.

Thermos Bottle
It keeps hot things hot and cold things cold.
But how does it know?

Indoor plumbing is the greatest invention! The donut would be second.

My vote is for the recognition of evolution. Relativity is the runner up.