One of those things I've known for awhile which other, less nerdy, people may not be aware of: "One study suggested that [humanity's ancient] population, worldwide, might have dropped as low as 40 adults. (The world record for fitting people in a phone booth is 25.)" The article includes a quick summary regarding why and how this conclusion was reached. Amazing coincidence, or divine intervention? Hey, the reason why the world's surviving religions have similar cores may be because only seven people originally thought them up.