This was one of FDR's favorite statements of the Allied Aims. They consisted of: freedom of speech, freedom of warship, freedom of want, and freedom from fear. The actual idea came from a picture made by Norman Rockwell, portraying different values of American life.
Follow @TIME. For our happiness issue, TIME conducted a poll to find out what Americans do to find joy. Overall, 59% of respondents said they were happy most of the time, about the same percentage of those surveyed by TIME in 2004 when 61% said they were happy. But fewer people said they considered themselves optimists in 2013, 50%, as compared to 2004 when 79% called themselves optimists.
The problem is, how do you calculate how many have ever lived, and where do you start? One group to have done the work is the Population Reference Bureau in Washington. Wendy Baldwin from the Bureau says that the normal starting point is when Homo sapiens first walked the earth, about 50,000 years ago. So you have a starting point and an end figure but it's the time in between that causes the problems. For 99% of that time there is no data, she says.