For me, the two most important events are the movement of modern human beings out of Africa and the "Great Leap Forward."
The movement of humans out of Africa was important because of the animals that it killed off. It was perhaps more important because of the fact that it determined which areas of the world got populated first. The late arrivals of human beings in Australia and the Americas, for example, had important impacts on the prospects for success of people in those areas.
The Great Leap Forward was one of the most important events in human prehistory. It somehow (we are not sure how) allowed for humans to develop much greater intellectual capabilities. This led the way to the eventual creation of true human societies and civilizations.