The bicameral mind

Birth control.

Zero. The concept of nothing is needed to make sense of anything.

Alternating Current- Electricity it lights the world and allows a much greater life!

I'd vote for the ability to make fire, when and where it was needed; then there's flint knapping, the beginnings of Science, investigating the 'grain in the stone.'

Symbolic representation of sound, ie... letters

writing

Memes

Gas powered ice auger, you would think so also if you ever used the manual labor ice auger.

The printing press

The neocortex, invented by Mother Nature, seems to have started our rise as dominant species on the Earth, and gave us the capacity for doing both art and science.

Language. It led to other developments.

Silicon chip

I would go for language. Though whether that counts as an invention or part of the natural course of evolution, I am not certain. Certainly a thought-provoking question!

Think the pencil is a brilliant design that is pretty much unchanged since it was created. Simple, functional... the other greatest invention is paper. Then there are books...

I love technologies but most will not function with out electricity. And that can be limiting. When you have a pencil, paper, and imagination the possibilities are endless.

Transistor

You mean apart from The Wheel, Electricity an the Internet? My "silly answer" is my MP3 player. If you had told me when I was young that you wound be able to fit all my 300 records (both sides) on something as small as a matchbox AND listen to them. I would have thought you were insane in the membrane. BIg Brighton Love Andy x

Yes, after reading some posts, I'm going with language and writing.

Wow, that's a good question, I need to think about it.

The boat! But then I'm biased.

It's a draw. Indoor plumbing and air conditioning. I was going to say donuts but that is so obvious.

Toilet paper was an excellent replacement for cactus.
P.S. I really did want to give an intellectual response but I'm tired and it's late, so the smart ass just came right out, Please forgive this episode.

That is an interesting question that I had not thought of until now. I would have to say that the greatest invention ever is the camera and how that morphed into video recordings. Not only do these things further our understanding of history but as a person that has researched the ancestry of over 50+ families - pictures bring it home. It's one thing to visit a cemetery for names and dates - it's quite another to have pictures of these people and how they lived and labored for us over 160+ years ago.

Good question. I wish I had an answer, but I don't. I will say that the one that has had the most profound and all encompassing effect on the development of civilization is written language. I'd say it was foundational.

Language/writing/communication, without it, nothing we have would be possible.