Human evolution is believed to have begun some six million years ago. Despite the passage of so much time, the amount of diversity among the DNA of all humans is minuscule.
Some 75,000 years ago, something apocalyptic occurred that left relative few humans alive to carry on the species.
The cause of this bottleneck is now believed to have been a massive volcanic eruption on the Indonesian island of Sumatra.
A super-eruption from the site of Lake Toba in Sumatra blasted out more than two hundred cubic miles of ash over an area of over a million square miles.
This program investigates the devastating aftermath of the most powerful volcano of the last twenty-five million years - including the theory that it triggered a human genetic bottleneck leaving a tiny band, as low as a few thousand survivors to preserve the human race - and looks at the threat of super-volcanoes in the 21st century.