probably out of context but if you ask me its gotta be verbal communication and then written language.
But in a perfect world, everyone would know the greatest scientific development to be Ayahuasca.

organized religion.

edit to say, I think it kept people in check enough for our current civilization to develop. as to its current usefulness, well I think it still keeps ignorant people in line.

[edit on 16-10-2009 by Totalstranger]

To enforce my opinion I recommend watching Ancient Inventions with Terry Jones E03. Not all of those inventions come from gunpowder but in war in general. If we weren't so violent we'd be still living in caves trying to figure out if our planet is square or not

I'll have to abstain from voting. Neither sliced bread, nor indoor plumbing is on the list. The voting list has been rigged by TPTB, and I'm sure that Obama is somehow involved!