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The Scientific Classification of Animals
In order to classify animals by their relationships and to make international understanding easier, zoologists have evolved a far-reaching system of Greek and Latin based names for animals and groupings of animals. This scheme not only gives every different kind of animal its own internationally known name but also fixes its position in relation to the rest of the Animal Kingdom.
Principal Categories
The principal categories are as follows. The Animal Kingdom is itself, of course, the largest of them, comprising all animals. The Kingdom is divided first into phyla. Although the majority of the commonly known animals fall into one phylum, the Chordata which includes the vertebrates or back-boned animals, there are many phyla at the more primitive and widely divergent end of the scale.
The phylum is divided into classes; one such is the class Mammalia, containing all the mammals. Classes are again divided into orders, distinguishing, for example, the Carnivora from the Primates.
Genus
The subdivision of the family is the genus, containing very closely related animals; and finally comes the species, which defines an animal exactly. The normal scientific way of referring to an animal is by its generic and specific names together. Thus the lion is Panthera leo. Panthera is the genus (which also contains the closely related tiger, leopard and jaguar), and leo, the specific name (and Latin for lion), narrows the field to the lion alone. So, Panthera leo belongs to the family Felidae, with all the catlike animals; the Felidae are part of the order Carnivora, with the other flesh-eating mammals; these join all other mammals in the class Mammalia, which in turn belongs with the birds, fishes, and others to the phylum Chordata; and the Chordata belong with all other animals to the Animal Kingdom, as opposed to the plants.
Species Evolution
All living things are forever on the move through time, most of them evolving into forms markedly different from their remote ancestors. Every individual organism carries a unique combination of traits inherited from its ancestors, which make it different from all other individuals. The parts of living cells carrying these traits are called genes; all of an organism's genes together form the genetic makeup. Every organism with two parents has received half of its genes from each one, and its genetic make up is different from that of either parent. Genes are reshuffled again and again in successive generations, with each individual offspring inheriting genes in unique combination from its parents and exhibiting traits that make it more or less adapted to survive.
The kind of change called evolution begins when a random accident occurs to the molecules carrying the genetic makeup. Such accidental alterations, or mutations, of the genes are caused by a variety of environmental influences.
The vast majority of mutations are harmful and often fatal to the organism in which they occur. A very small percentage of mutations that are beneficial, however, improves the ability of the new organism to adapt to environmental conditions. With enhanced powers of survival, such organisms are likely to pass on the mutant genes to their offspring.
As additional mutations reinforce earlier ones, the process of diversification is fostered within the mutant group. Natural selection becomes increasingly influential: The individuals that are most successful in a given set of conditions, birds with beaks strong enough to crush seeds, predator or prey with a good camouflage coloration, multiply and flourish. But organisms that are not so fit in one respect may, instead of dying off, become specialists in another direction and survive as another branch of the family tree.
In time, both groups make take forms strikingly different from their pioneering cousins, and relationships may be nearly or quite impossible to trace.
There are probably 10 million species in the kingdom of animals. About 1.2 million of them have been named and described by the scientific community, but the total number can only be estimated because much of the world has not yet been properly surveyed. New techniques are constantly being developed for examining previously uncharted regions that were thought to be barren. For example, remote-control submarines are revealing some of the remarkable species to be found in the ocean depths, and the diverse communities of bacteria, protists and fish to be found in hydro-thermal vents on the sea floor.
In lakes and oceans diversity is higher near the surface, particularly in the "photic" zone (the top 100 feet or 30 meters), where the photosynthesis takes place. On land, diversity tends to be at its lowest in temperate and polar regions. IN the tropics, where there is reliable moisture and warm, stable temperatures, animal diversity is much higher. Species living in these regions do not need the broad characteristics necessary for coping with various conditions (such as drought, or winter temperatures) and adapt and diversify to suit local conditions (such as a particular type of tree or ground cover).
Extinction of Species
While the rate of extinction through natural process is estimated as less than one species a year for every million of species, habitat destruction has led to a current annual extinction rate of between 1,000 and 10,000 per million species. The disappearance of some species
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Animal Calendars
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