| | | Animals are a major group of organisms, classified as the kingdom animalia. They are generally multicellular, which means they contain more than one cell, and their cells perform differentiated functions. Most multicellular organisms, which include all animals and plants, contain several groups of cells, with each group performing a different task. These groups of cells working together are called tissues. Animals are also capable of locomotion, and are responsive to their environment. They feed by consuming other organisms.
Aristotle was the first to attempt to classify living things, separating animals from plants. He further divided animals by whether they lived in water, on the ground, or flew in the air. It was until nearly two thousand years later, that Carolus Linnaeus would create the first system of classification of animals. Over more recent years, Linnaeus' classifications have been revised several times based on newer evolutionary relationships, such as the Darwinian theory of common origin.
Animal comes from the Latin word animalis and its plural animalia, which first comes from anima, meaning vital breath. |
| Except for a few groups such as sponges, most animals share the same body structure. As they are multicellular, they contain many tissues, and so their bodies can be divided into several systems. There are muscles, which can contract, and control movement of the animal, or locomotion. Most animals also possess a nervous system that sends a processes signals, allowing control over various tissues and other systems. They also usually contain an internal digestive chamber. |
| Almost all animals undergo some form of sexual reproduction. The males and females of each species contain special reproductive cells that, as a result of meiosis produce either sperm, or ova. These two fuse together to form zygotes, essentially a new individual. In most forms of animals this process also involves social and emotional aspects and is called "mating." Zygotes of many species are often referred to, by the lay community as "babies." |
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