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.
Ancestors - The people related to us who lived a long time ago.
Astronomer - A scientist that studies the universe and space.
Science fiction - Stories based on major scientific or technological changes.