Concept

Animal

Overview

Animals are multicellular, eukaryotic organisms belonging to the biological kingdom Animalia (). Animals consume organic material, breathe oxygen, have myocytes, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. With few exceptions, animals are able to move. Animals form a clade, meaning that they arose from a single common ancestor. Over 1.5 million living animal species have been described, of which around 1.05 million are insects, over 85,000 are molluscs, and around 65,000 are vertebrates. It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex ecologies and interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology, and the study of animal behaviour is known as ethology.

The animal kingdom is divided into five major clades, namely Porifera, Ctenophora, Placozoa, Cnidaria and Bilateria. Most living animal species belong to the clade Bilateria, a highly proliferative clade whose members have a bilaterally symmetric and significantly cephalised body plan, and the vast majority of bilaterians belong to two large clades: the protostomes, which include organisms such as arthropods, molluscs, flatworms, annelids and nematodes; and the deuterostomes, which include echinoderms, hemichordates and chordates, the last of which contains the vertebrates. The much smaller basal phylum Xenacoelomorpha have an uncertain position within Bilateria.

Animals first appeared in the fossil record in the late Cryogenian period and diversified in the subsequent Ediacaran period in what is known as the Avalon explosion. Nearly all modern animal phyla first appeared in the fossil record as marine species during the Cambrian explosion, which began around 539 million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. Common to all living animals, 6,331 groups of genes have been identified that may have arisen from a single common ancestor that lived about 650 Mya during the Cryogenian period.

Historically, Aristotle divided animals into those with blood and those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between taxa.

Humans make use of many other animal species for food (including meat, eggs, and dairy products), for materials (such as leather, fur, and wool), as pets and as working animals for transportation, and services. Dogs, the first domesticated animal, have been used in hunting, in security and in warfare, as have horses, pigeons and birds of prey; while other terrestrial and aquatic animals are hunted for sports, trophies or profits. Non-human animals are also an important element of human culture, having appeared in cave arts and totems since the earliest times, and are frequently featured in mythology, religion, arts, literature, heraldry, politics, and sports.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

In the original texts

Passages from public-domain books where Animal is discussed.

1. These fluids are nearly always co-existent with animal life; but milk and the spermatic fluid are produced afterwards. Of these the milk is always secreted in those animals in which it is present. The spermatic fluid is not secreted in all, but in some as in fishes are what are called melts. All animals having milk have it in the mammæ.
Aristotle, Aristotle's History of Animals In Ten Books
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2. An animal that dies accidentally is mourned and buried with the same honours as a member of the tribe. 3. The prohibition as to eating sometimes refers only to a certain part of the animal. 4. If pressure of necessity compels the killing of an animal usually spared, it is done with excuses to the animal and the attempt is made to mitigate the violation of the taboo, namely the killing, through various tricks and…
Sigmund Freud, Totem and taboo
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In its most rudimentary form, the animal is a tiny mass of protoplasm enveloped at most in a thin albuminous pellicle which allows full freedom for change of shape and movement. The vegetable cell, on the contrary, is surrounded by a membrane of cellulose, which condemns it to immobility.
Henri Bergson, Creative Evolution
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In the above-mentioned development of totemism (which is at the same time a retrogression) the totem animal becomes individualized. The protective animal--or the animal of destiny, as we might refer to it, in view of its many changes in meaning--is but an individual animal. A person may possibly never have seen the animal that keeps guard over him; nevertheless, he believes that it is always near at hand. The unseen…
Wilhelm Max Wundt, Elements of Folk Psychology Outline of a Psychological History of the Development of Mankind
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There are first of all the movements which are "mechanical," such as slipping and falling, where ordinary physical forces operate upon the animal's body almost as if it were dead matter. An animal which falls over a cliff may make a number of desperate struggles while it is in the air, but its centre of gravity will move exactly as it would if the animal were dead. In this case, if the animal is killed at the end of…
Bertrand Russell, The Analysis of Mind
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Animal

Overview

In the original texts

Philosophers who discussed Animal

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Place in the tradition