Science journalist Angela Saini and disability rights activist Adam Pearson, reveal that eugenics - the controversial idea that was a driving force behind the Nazi death camps - originated in the upper echelons of the British scientific community.
Previously it was thought that only 2% of our DNA is meaningful and the remaining 98% is non-coding “junk”. But today we are beginning to know how the junk part of our DNA works to decide our personal characteristics and tendencies.
In part two, Professor Al-Khalili looks at the 19th century chemists who struggled to impose an order on the apparently random world of the elements. From working out how many there were to discovering their unique relationships with each other, the early scientists' bid to decode the hidden order of the elements was driven by false starts and bitter disputes. But ultimately the quest would lead to one of chemistry's most beautiful intellectual creations - the periodic table.