“My favorite invention was paper. It didn’t occur to me at first. People said to me, ‘You must put the printing press in the book. It revolutionized the way we think; it led to the Reformation and rise of Europe.’ But without paper, the press isn’t very useful. Yes, you can print on animal skin. But 5,000 copies of a book will require a quarter of a million sheep. Paper is what makes the printing press economically feasible. It’s an extremely underrated invention. Also, it has other practical uses, like toilet paper.” Derek Thompson talks to economist Tim Harford about his book on the greatest breakthroughs in human history, including barbed wire, air conditioning, and money. (Somehow, Retweets didn’t make the list.)