However, excessive hunting and poachers have also contributed heavily to the endangerment, extirpation and extinction of many animals, such as the quagga, the great auk, Steller's sea cow, the thylacine, the bluebuck, the Arabian oryx, the Caspian and Javan tigers, the markhor, the Sumatran rhinoceros, the bison, the North American cougar, the Altai argali sheep, the Asian elephant and many more, primarily for commercial sale or sport. How is excessive hunting related to the extinction of species?