According to the passage, the dominant belief among scientists is that……….. .

Fossil analysis reveals that at least five periods in the last 600 million years have seen a drastic reduction in the number of species of flora and fauna on the Earth. However, on previous occasions such changes were brought about by asteroids or dramatic climatic changes. Experts in general believe that this decline is the work of man. The dominance of a single species type, homo sapiens, threatens to turn the rest of the living world upside down. With a population of barely six billion, humans are rapidly destroying irreplaceable ecosystems. This sixth round of global dying of species could be far larger than the first five.