Language is certainly an achievement, but we're talking about scientific and technological discoveries. After all, speech appeared in primitive people for, roughly speaking, herding prey, and it's impossible to name the one who developed such a concept as language... This is not a discovery, but rather an evolution...
But writing is a different matter!
But I chose the following:
1) The discovery of penicillin (antibiotics are a very important discovery, saving the lives of many people)
2) The invention of electricity (no comment)
3)