Animals in Danger of Extinction①—The Causes The famous biologist②,E.O.Wilson says the causes of animals in danger of extinction can be explained using the acronym H-I-P-P-O,Hippo.Here is what Hippo stands for: H=Habitat③:There are many reasons animals become extinct.One of the most common reason is loss of habitat. I=Invasive Species:An invasive④ species is a type of plant,animal,insect or disease that moves into a new area,where it has not lived before,and over takes other living things. P=Pollution:Exposure to toxic(有毒的) pollution is another cause of extinction.Human activity is releasing harmful chemicals into the air,water and soil all over the planet.Many animals cannot adapt to the changes these chemicals are making in the environment and they die.