The growth of the human population has not always been a smooth ride, but has been punctuated by some strange fluctuations. At multiple points in our history, populations have dramatically imploded . One such period occurred during the Neolithic, around 5,000 years ago, when communities collapsed across parts of Europe. The reason – or reasons – for this widespread phenomenon have long remained something of a mystery, although several hypotheses for what scientists call the ' Neolithic decline '