So how many species exist today anyway? Scientists have identified and classified somewhere between 1.4 and 1.7 million different species of plants, insects, animals, algae, fungi, and microorganisms. Some estimate the total at about 4 or 5 million. Many biologists think there are 10 million or more. Terry L. Erwin of the Smithsonian Museum of Natural History has the highest estimate, suggesting that the total number of living species on the planet is at least 30 million.

         But these numbers are dropping at alarming rates. Just how fast are species really disappearing? A biologist at Harvard University named E.O. Wilson believes at least 4,000 to 6,000 species become extinct each year as a result of the destruction of the tropical rainforest alone. He thinks the actual worldwide extinction rate could be much higher. Peter Raven, the director of the Missouri Botanical Garden, believes species are becoming extinct at the rate of 100 per day, which is about 1 species every 15 minutes. Jared Diamond, a physiologist at the University of California in Los Angeles, feels that if the present trends continue, at least 50% of all currently existing species will be either extinct or endangered by the year 2050. Some estimates indicate that perhaps as much as one-fifth of all the species on earth today will have vanished by the end of the century.

         Over 19,000 plant species and 5000 animal species around the globe are classified as endangered, and many thousands more become extinct each year before biologists can identify them. No more than one-tenth of the estimated 10-50 million species of invertebrates (animals with no backbones such as insects and mollusks) have even been described.

         Unfortunately, the crisis is most severe in the earth's tropical rainforests. It is here that the densest concentration of species exists, serving as home to at least 50% of all living species - perhaps, some believe, as many as 80%.

Definition

Basic Biology - Classification