Robert Rylands, Jr., age 10, of Allison Park, Pennsylvania, for his question:
How many animal species are living?
Not so long ago, everybody assumed that at least all the sizable animals had been found and identified. Then somebody discovered the mule sized okapi and somebody else introduced the whopping komodo dragon to the world. Maybe other large species are still in hiding. But certainly we have not found all the small creatures. Hundreds of newcomers are added to the list of known insects every year.
Naturally we can list only the known animal species and we can only estimate the number because next year the list will probably be longer. As of now, the estimated number of known animal species is somewhat larger than one million. The familiar cats and dogs, farm animals, lions and tigers and other mammals account for only about one 200th of the total count. The furry ones are outnumbered by the feathery birds and far outnumbered by the scaly fishes.
A million is a large number that does not make much sense by itself. So let's break it apart to get a more lively picture of the various types of species. The smallest members of the animal kingdom are the single celled protozoa, most of them too small for human eyes to see. Scientists have described about 80,000 species and the investigation into this world of midgets has barely begun.
The vertebrate animals, with internal bones and spines, are all big enough to be seen though most scientists suspect that we have not seen all of them. This assortment of species includes a group of 1,500 amphibians, such as the frogs and toads and other gentle creatures that are at home both in water and on land. Another group of 6,000 or so reptiles includes the scaly snakes and lizards. So far, about 8,600 feathery birds have been identified, but nobody expects this list is completed. About 5,000 mammal species have been identified and we know that there are at least 20,000 fish species in the salt and fresh waters of the world.
The complete assortment of vertebrates is far outnumbered by the spineless, or invertebrate, animals. This list includes the clams and a multitude of mollusks, the stately snails plus a vast variety of shellfish, starfish and polyps that hide in the sea. More than 90 per cent of the known animal species are invertebrates. And most of these are insects. At present, scientists have identified about 700,000 different insects and at least one newcomer is added to the list every day. The insects belong in a class of their own and they far outnumber all the other species that share our planet.
It is helpful to identify the species and add up the total. But studying the role of each species in nature is more important and also more rewarding. Each animal shares a give and take existence with other species and assorted plants in his natural environment. Naturally we want all existing species to survive. We can help in this struggle when we understand their roles in the ecology. Then we can work with nature to maintain balanced populations of different species where they belong.