This is a very strange statement with which i strongly disagree.
You are correct that our ancestors 100,000 years ago were equally capable of all the complex tasks that we do today, but they did not do it. I assume this is why you made this statement.
However, over the many thousands of years that man lived in small groups as nomadic hunter-gatherers, gradually new ideas, words ways of manipulating nature were picked up and adopted. Sometime between 5-10,000 years ago a critical mass was reached. There was enough knowledge present that the mastery of agriculture sparked a situation in which greater food production and specialization got the ball rolling toward the civilization where we now find ourselves.
Within our own period of civilization we have had stagnant ages followed by eras of rapid change. For the most part, however, expierience and a building up of knowledge and history have only accelerated the process. The changes since the industrial revolution (about 300 years) have been greater than the entire preceeding period of human history.
One could look at that period and say something dramatic must have happened to cause it. But, the reality is that enough knowledge graudal knowledge, combined with one or two innovative inventions sparked it. So we needn't look to climate change or aliens to answer why certain things happened in human histroy. It is just a process by which a creative, intelligent species is growing and maturing - guided by the hand of God.