The passenger pigeon, which once numbered in the billions in Norther America, has become a symbol of extinction. It was wiped out in the 19th century due to overhunting.
Animals face many natural threats, including changing temperatures, predators, and unexpected disasters. But no external stresses have proved more destructive to the survival of other living things than people.
The following gallery includes other animals that have gone extinct almost directly by the hands of humans.