Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also heterotrophs, meaning they must ingest other organisms or their products for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago.
Read more about Animal: Etymology, Characteristics, Origin and Fossil Record, Model Organisms, History of Classification, Ethics
Famous quotes containing the word animal:
“You don’t want to be an animal, you want to observe your own animal functions, so as to get a mental thrill out of them. It is all purely secondary—and more decadent than the most hide-bound intellectualism.”
—D.H. (David Herbert)
“To revolt is a natural tendency of life. Even a worm turns against the foot that crushes it. In general, the vitality and relative dignity of an animal can be measured by the intensity of its instinct to revolt.”
—Mikhail Bakunin (1814–1876)
“To the men of this world, to the animal strength and spirits, to the men of practical power, whilst immersed in it, the man of ideas appears out of his reason. They alone gave reason.”
—Ralph Waldo Emerson (1803–1882)