Is our existence a miracle? Humans rule the world. But new research shows that many years ago we could have died out. Some think that we should be amazed by just how lucky we are to exist.
Early humans nearly wiped out, say scientists
Survivors: Today, there are 8.1 billion people worldwide, from a low of just over 1,000. Glossary
Extinct - A species that no longer has any living members.
Population - All of the people that live in a place.
Science fiction - Stories based on major scientific or technological changes.