A zoological garden, shortened to zoo, is an institution in which living animals are exhibited in captivity. In addition to their status as tourist attractions and recreational facilities, modern zoos may engage in captive breeding programs, conservation study, and educational outreach. Zoos are a subject of controversy stemming from many sources, including the quality of life of the animals they exhibit, and the perceived necessity or purpose of exhibiting captive animals at all. Zoos are frequently criticized by animal rights groups. [1]
Collections of wild animals existed already in the ancient civilizations of Mesopotamia, Egypt, and China. In medieval Europe some monarchs, monasteries, and municipalities continued to maintain collections of wild animals. The transition from menagerie, a predominantly private collection, to public institution marks the beginning of the modern zoo concept. Collections established during the nineteenth century began calling themselves zoological gardens. Throughout the nineteenth and twentieth centuries, many new zoos and related facilities were founded for very different motives and purposes.
Zoo professionals proclaim demanding aims for their institutions, from educating the public to conservation of biodiversity. Many zoos define their aims as recreation, education, research, and conservation. Animal-rights groups claim that there is a wide gap between these claimed aims and actual practice, and that zoos have commercial and entertainment purposes in mind as well as financial profit.
Types of zoo include urban, open-range, safari, animal theme, roadside, rescue, sanctuary, petting, and specialized. The most traditional form of maintaining wild animals in captivity is keeping them in cages constructed of concrete or metal, in aviaries, or fenced paddocks. Most zoological gardens incorporated within international umbrella organizations are led by professionals such as zoologists or veterinarians.
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. Animals are also heterotrophs, meaning they must ingest other organisms for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years.
Origin and fossil record
Animals are generally considered to have evolved from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates, collared flagellates that have a morphology similar to the choanocytes of certain sponges. Molecular studies place animals in a supergroup called the opisthokonts, which also include the choanoflagellates, fungi and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal spermatozoa, whereas other eukaryotes tend to have anterior flagella.
The first fossils that might represent animals appear towards the end of the Precambrian, around 610 million years ago, and are known as the Ediacaran or Vendian biota. These are difficult to relate to later fossils, however. Some may represent precursors of modern phyla, but they may be separate groups, and it is possible they are not really animals at all. Aside from them, most known animal phyla make a more or less simultaneous appearance during the Cambrian period, about 542 million years ago. It is still disputed whether this event, called the Cambrian explosion, represents a rapid divergence between different groups or a change in conditions that made fossilization possible. However some paleontologists and geologists would suggest that animals appeared much earlier than previously thought, possibly even as early as 1 billion years ago. Trace fossils such as tracks and burrows found in Tonian era strata in India indicate the presence of triploblastic worm like metazoans roughly as large (about 5 mm wide) and complex as earthworms.[7] In addition during the beginning of the Tonian period around 1 billion years ago (roughly the same time that the trace fossils previously discussed in this article date back to) there was a decrease in Stromatolite diversity which may indicate the appearance of grazing animals during this time as Stromatolites also increased in diversity shortly after the end-Ordovician and end-Permian rendered large amounts of grazing marine animals extinct and decreased shortly after their populations recovered. However some other scientists doubt that these fossils are authentic and have suggested these trace fossils are just the result of natural processes such as erosion.
