I think many of you have already read that but if not, I let this article to explain:
http://www.vox.com/2014/7/30/5951263/a- ... th-in-2012
and there are even more when using Google
http://www.forbes.com/sites/bridainepar ... dark-ages/
sorry if links aren't reliable, I used to read science articles about this in my native language and I just tried to find some links for you english speakers