The outright elimination of habitat is the leading cause of extinction. But the introduction of aggressive exotic species and the diseases they carry follow close behind in destructiveness, along with overhunting or overharvesting of plants and animals. All these factors work together in a complex manner. A common sequence in tropical countries starts with the building of roads into wilderness, such as those cut across Brazil's Amazonian state of Rondonia during the 1970s and '80s. Land-seeking settlers pour in, clear the rain forest on both sides of the road, pollute the streams, introduce alien plants and animals and hunt wildlife for extra food.
Many native species become rare, and some disappear entirely.
The world's fauna and flora are paying the price of humanity's population growth. The levy may be acceptable to those who put immediate human concerns above all else. But it should be borne in mind that we are destroying part of the Creation, thereby depriving all future generations of what we ourselves were bequeathed. The ongoing loss in biodiversity is the greatest since the end of the Mesozoic era 65 million years ago. At that time, by current scientific consensus, the impact of one or more giant meteorites darkened the atmosphere, altered much of earth's climate and extinguished the dinosaurs.