It could have been human beings who thought that they needed their homes more than the animals needed theirs. Or, it could have been people who didn't understand that their pollution could cause so much damage. Pollution of the air, water, and soil can cause many problems. For example, when crops are sprayed with pesticides, these poisons get into seeds that are eaten by birds and they die. The oceans and lakes are being polluted and this kills the fish.
Extinction is a natural event that has happened since the beginning of time.
When an animal, like the dinosaur, became extinct, it was from a natural cause like an earthquake or volcano or flood. It s different today. Some people hunt animals to make money by selling the skins or other parts of the animals. They don t do it because they re hungry or need the fur to keep them warm. They are called poachers.