Due primarily to the impact of man on the natural environment, whether directly or indirectly, a large number of species of animals are in danger of extinction.
Since 1600 (when reliable zoological records began) about one percent of the higher animal species alive at that time have become extinct and another 2.5% are now in danger. These figures are for full species, but geographical races have fared even worse. About 25% of the 130 lost species disappeared through natural causes (since extinction is a natural part of evolution). The remainder have died out directly or indirectly as a result of man's avoidable actions: hunting, habitat disruption, introduction of species predators and competitors. Of the 304 species under threat today, 66% of the birds and 83% of the mammals are in their present state because of man's activities. About 75 species were wiped out by humans during the nineteenth century. So far in the twentieth century, the pace has accelerated, with approximately one species vanishing each year, a rate experts predict will increase drastically by the year 2000. According to a recent environmental study, 20% of all species on earth could become extinct during the next two decades, a loss unparalleled in human history. Many ecologists have predicted half a million extinctions in tropical rain forests alone by the end of the century—an average loss of about one hundred species per day. The rate of impact of these activities on the natural environment is accelerating.