Animal

[[File:Animal diversity composite.png|thumb|200px]]
{{biology}}
'''Animals''' (from the [[Latin]] ''animale'' for "having breath")<ref group=note>See [https://www.etymonline.com/search?q=animal Online Etymology Dictionary] discussion. The Latin root-word ''anima'' can mean "breath" or "soul", hence some scope for theological confusion over whether non-human animals can have souls and whether humans alone have divinely-imparted souls/breath. Compare concepts like {{wpl|inspiration}} — literally "breathing in" or "[[spirit]]".</ref> are a diverse group of [[life]] on [[Earth]], consisting currently of around two million known [[species]] belonging to the biological kingdom '''Animalia''', also known as '''Metazoa''' (literally "following animals", see below). Most of these species are [[insect]]s; many of those are beetles. Animals are all motile at some point during their lives, have many cells (except in the [[zygote|zygotic]] stage), [[heterotroph|get their nutrients from other sources]] and have [[cell theory|cells]] without walls. However, the definition of "animal" has changed over the centuries.

== History and definition ==
In all likelihood, [[human]]s have recognised the basic concept of "animal" as long as we have had the capacity to do so, by [[tautology|circular definition]], long before we knew anything about cells. Woolly mammoths move around, eat food, and when [[death|killed]] can be considered meat. This made "animals" (such as edible [[insect#Locusts|locusts]]) distinct from "bugs". This simple, [[intuition|intuitive]] method would have worked well enough for our hunter-gatherer ancestors, because it was important to recognize what you can eat and {{wpl|Smilodon|what can eat you|.}} When humans begun to take a look at the seas, they saw that things like "[[God hates shrimp|shellfish]]" didn't noticeably move, but were still a form of "meat". "Animals" could be considered as having a "flesh and blood", as reflected in a [[Bible|biblical]] statement, Genesis 9:2-4:

{{cquote|...the dread of you <nowiki>[</nowiki>[[Noah]] and his family] shall be upon every beast of the earth, and upon every fowl of the air, upon all that moveth upon the earth, and upon all the fishes of the sea; into your hand are they delivered. Every moving thing that liveth shall be meat for you.… But flesh with the life thereof, which is the blood thereof, shall ye not eat.|||Genesis 9:2-4, [[King James Only|KJV]]}}

An early attempt to [[taxonomy|classify life]] came in 350 [[BCE]] from [[Aristotle]], who put living things into two groups: "[[plant]]s" and "animals".<ref>[http://classics.mit.edu/Aristotle/history_anim.html Read the book in English online]</ref> Aristotle used methods based on superficial characteristics, like habitat, means of movement, and whether or not subjects have red blood.

Aristotle's natural history was mostly forgotten in the [[Dark Ages]], mainly retained by the [[Catholicism|Church]] to specify what good Christians can or can't eat during [[Lent]]. 

Some circles have tended to characterise animals using the word "creature" (implying a sense of things [[creation|created]]), which has the advantage of grouping humans with other animals; whereas the term "beast" emphasises the "sub-human" characteristics of large vertebrates.

In the [[Enlightenment]], due to mounting importance of observation-based and evidence-based knowledge, the need for a better system of classification reemerged. {{wpl|John Ray}} first coined the term "species" biologically and classified plants in ''Historia Plantarum'' (published in 1686), using a system based on similarities and differences on close observation rather than predefined "kinds" or "types". Ray's work would later influence {{wpl|Carl Linnaeus||,}} who published the first edition of his ''[[Linnaean taxonomy|Systema Naturae]]'' in 1735, which established "Animalia" and "Vegetablia" as the two "kingdoms" of life.{{efn|Linnaeus also included a "mineral kingdom" to classify the inorganic natural world, but science has since abandoned it.}} Linnaeus initially divided his animal kingdom into six classes:

* '''Quadrupedia''' (all mammals excluding the whales and dolphins, initially classified as fish)
* '''Aves'''
* '''Amphibia''' (including reptiles)
* '''Pisces''' (remaining vertebrates ''[sensu stricto]''){{efn|"Vertebrata" is considered distinct from "Craniata", as supported by some (not all) genetic and morphological analyses. (The other hypothesis is that lampreys and hagfish are closely related, forming one group, Cyclostomata. This is supported by other, mostly genetic, analyses. You can argue either way with fair levels of [[evidence|support]].) The hagfish are included in the latter but not the former. When Linnaeus added the hagfish, he included them in "Vermes".}}
* '''Insecta''' (= Arthropoda ''[sensu praesens]''){{efn|[[Latin]], "in the present sense".}}
* '''Vermes''' (the rest of the modern animal kingdom not in the above groups, plus amoebae)

The tenth edition of the Linnean ''Systema'', published in 1758, also saw the true establishment of binomial nomenclature still used today to name species. As the decades passed, biologists added the taxonomic levels of family and phylum, split up Vermes into various groups, and made many other such changes. As of ''c.'' 1980, [[zoology]] divided "animals" into the following subkingdoms:

* '''Protozoa''' ("first animals"), undifferentiated [[eukaryote]]s that do not have rigid cell walls or produce filamentous threads. Members have no embryology, so the {{wpl|Myxozoa}} were included in their ranks.
* '''Mesozoa''' ("middle animals", believed to be midway between protozoa and "true animals"), simple many-celled vermiform parasites of [[mollusc|cephalopods]] and others. Members have a very simple [[embryo]]logy. 
* '''Parazoa''' ("near/beside animals", believed to be the closest relatives of "true" animals), including the [[sponge]]s (phylum Porifera) and the ''{{wpl|Trichoplax|Trichoplax adhaerans|'';}} these simple animals had many cells and an embryology including a {{wpl|gastrula||,}} but no true differentiated tissues.
* '''Metazoa''' ("following animals", because they followed the parazoa in chronological order) included all modern animals except sponges and trichoplaxes (see Parazoa, above). Now considered equal to the modern Eumetazoa.

Since about 1990, [[evolution]]ary relationships have become an integral part of taxonomy. The field of [[cladistics|phylogenetics]] has taken over, which led to the Protozoa and Metazoa being dissolved and split into various groups. The modern kingdom Metazoa includes 1980s Metazoa, Mesozoa, Myxozoa, and Parazoa. The word "protozoan" is still sometimes used as an informal group, or evolutionary "grade".

=== Modern definition ===
As stated in the introduction, the modern Kingdom Metazoa includes permanently (excluding the [[zygote]]) many-celled organisms that undergo development (including at least one motile stage) in their life history. All the Metazoa and only the Metazoa produce a structural protein, collagen (this criterion prevents creatures like the ''Volvox'' from being animals as Linnaeus classified them). Typically, the "animals" are listed as being heterotrophic (i.e, needing to organic material to survive), although lineages like the {{wpl|Pogonophora|beard worms|,}} {{wpl|Elysia (genus)|emerald sea slugs|,}} and possibly the Ediacaran biota (see below) house bacteria that produce their nutrients from within so these lineages do not need to eat other organisms.

Today, animals are classed into roughly 36 phyla,{{efn|As there are many debates as to whether certain extinct creatures belong to their own phyla, the exact number depends on who you ask.}} although only nine of them contain the majority of living animals.<ref>[http://www.fossilmuseum.net/Tree_of_Life/Kingdom_animalia/animalphyla.htm Animal Phyla], ''Fossil Museum''</ref> These are:

* '''{{wpl|Porifera||''':}} This phylum contains [[sponge]]s. Sponges remain stationary throughout their life and rely on flowing water rather than a complex nervous, digestive, or circulatory system, making them often considered the "simplest" animals alive today.<ref>[https://oceanservice.noaa.gov/facts/sponge.html What is a sponge?], ''National Ocean and Atmospheric Administration''</ref>
* '''{{wpl|Cnidaria||''':}} Derived from the Greek word for "stinging nettle", this phylum contains coral, jellyfish, sea anemones, and other similar animals that are distinguished by their stinging cells. Cnidarians have either the {{wpl|polyp}} or {{wpl|medusa}} form, with stinging cells on their tentacles.<ref>[https://ucmp.berkeley.edu/cnidaria/cnidaria.html Introduction to Cnidaria], ''Hydrozoan Society''</ref>
* '''{{wpl|Arthropoda||''':}} By far the most diverse animal phylum, comprising over 80% of known extant animal species, it contains [[insect]]s, arachnids, [[crustacean]]s, millipedes, trilobites, and more. Arthropods have exoskeletons made of {{wpl|chitin}} and grow by molting.<ref>[https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/phylum-arthropoda Phylum Arthropoda], ''Exploring our Fluid Earth''</ref>
* '''{{wpl|Nematoda||''':}} This phylum contains roundworms, which are very adaptable animals that can be found almost anywhere on Earth. They are distinguished from other worms by their tubelike digestive system.<ref>[https://ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html Introduction to the Nematoda], ''University of California Berkeley''</ref>
* '''{{wpl|Annelida||''':}} These are the segmented worms, which include earthworms and leeches, among others. Unlike the nematodes, their bodies are made of segments which each contain the same organs.<ref>[https://nhpbs.org/wild/annelida.asp Annelida - Segmented Worms], ''PBS''</ref>
* '''[[Mollusc]]a''': This phylum contains bivalves such as clams, gastropods such as snails, and cephalopods such as squids, alongside a few other groups like chitons. They are distinguished by their mantles, which in most mollusc species produces a hard shell.<ref>[https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/phylum-mollusca Phylum Mollusca], ''Exploring our Fluid Earth''</ref>
* '''{{wpl|Platyhelminthes||''':}} This phylum contains flatworms, which include our friends the [[Helminthic therapy#Organisms unsuitable for therapeutic use|tapeworms]] and flukes alongside a few non-parasitic ones as well. Unlike the other worms, they don't have an internal body cavity containing their organs.<ref>[https://ucmp.berkeley.edu/platyhelminthes/platyhelminthes.html Introduction to the Platyhelminthes], ''University of California Berkeley''</ref>
* '''{{wpl|Echinodermata||''':}} These include sea stars, sea urchins, sea cucumbers, sea lilies, and more, and are more closely related to vertebrates than any of the previously mentioned phyla. They are distinguished by their {{wpl|radial symmetry}} and skeletons composed of {{wpl|ossicles||.}}<ref>[https://ocean.si.edu/ocean-life/invertebrates/echinoderms Echinoderms], Danielle Hall ''Smithsonian Ocean''</ref>
* '''[[Chordata]]''': The phylum that includes [[human|us]], as well as all other vertebrates and a couple of invertebrates like lancelets and sea squirts. All chordates have a {{wpl|notochord||,}} a hollow {{wpl|dorsal nerve cord||,}} {{wpl|pharyngeal slits||,}} a post-anal tail, and an {{wpl|endostyle}} or {{wpl|thyroid||.}} The main group is vertebrates, which contains mammals, birds, reptiles, amphibians, and fish.<ref>[https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/phylum-chordata Phylum Chordata], ''Exploring our Fluid Earth''</ref>

A few smaller, but nonetheless important phyla include:

* '''{{wpl|Bryozoa||''':}} These are tiny filter feeders called zooids which build large colonies of thousands, leaving behind a skeleton known as a zooecia. They are common [[fossil]]s and are still decently widespread today, even if they are frequently overlooked.<ref>[https://mdc.mo.gov/discover-nature/field-guide/bryozoans-moss-animals Bryozoans (Moss Animals)], ''Missouri Department of Conservation''</ref>
* '''{{wpl|Brachiopoda||''':}} This contains brachiopods, which look superficially similar to clams but differ greatly in terms of their internal structure. They were widespread throughout the Paleozoic, but are uncommon today.<ref>[https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/brachiopods/ Brachiopods], ''British Geological Survey''</ref>
* '''{{wpl|Hemichordata||''':}} Containing acorn worms, pterobranchs, and a few others, this phylum was thought to be the most closely related to chordates but genetic analysis revealed that these are more closely related to echinoderms. Their bodies have three parts, a preoral lobe, a collar, and a trunk, and they have a few structures reminiscent of chordates, such as a {{wpl|stomochord||,}} which resembles a notochord.<ref>[https://ucmp.berkeley.edu/chordata/hemichordata.html Introduction to the Hemichordata], ''University of California Museum of Paleontology''</ref>

=== At law ===
Animals are chattel property.  Wild animals freely roaming are considered the common property of all, and those who manage to capture or kill one acquire it as their property.<ref>''Bostock-Ferari Amusement Co. v. Brocksmith'', 34 Ind. App. 566, 73 N.E. 281 (1905)</ref>  Given animals' status as items of chattel property, the human owners of animals are entitled to kill them, for food, sport, or any reasons; these rights, however, are subject to the police power of the state, which may restrict them in order to guard public health, welfare, or morality.<ref>
''Youngstown v. Traylor'', 123 Ohio St. 3d 132, 914 N.E.2d 1026 (2009)
</ref>

== Origins ==
There are two leading [[manufactroversy|opinions]] regarding the origins of animals: the [[evolution|explanation supported by hundreds of thousands of peer-reviewed papers by thousands of scientists over 150+ years from all walks of life, gathered and refined through the most rigourous methods possible]] and the [[bullshit]] explanation.

=== Reality ===
The kingdom Metazoa's oldest fossil record appears in the Ediacaran period, 630 million to 542 million years ago. As indicated by [[genetics|genetic]] and [[fossil record|fossil]] records, the first animals were invertebrates not unlike sponges, jellyfish, and sea pens. The very first animals with a distinct head and tail appeared {{wpl|Vernanimalcula|600 million years ago|.}} Over a period of time lasting up to 80 million years, these bilaterians diversified into various body plans and gained hard parts like armour, shells, and bone. This important evolutionary process has been named the [[Cambrian explosion]] because initially, before soft-bodied fossils were discovered, it appeared several major groups of animals appeared to appear from nothing. Appearances are deceiving, however. Animals have since diversified from then on, eventually branching out into the groups we know today.

=== Bullshit ===
[[Young Earth creationism|Some people]] believe with no [[empiricism|empirical]] [[evidence]] to support their views that [[YHWH|some old psychopath]] poofed every living thing into existence over a period of [[Creation Week|six days]]. Animals are said to have been created over the fifth and sixth days of this week. [[Human]]s are also believed to be distinct from animals because humans have the ability to be "[[born again]]" and accept [[God]] into their hearts. These claims are with absolutely no supporting evidence, and have massive [[common descent|refuting evidence]], although they somehow gain [[Answers in Genesis|quite a following]].

== See also ==
* [[Cryptozoology]]: The [[pseudoscience]] of studying animals that probably do not exist.

==Notes==
{{reflist|group=note}}

==References==
{{reflist|2|80%}}

[[Category:Animals|*]]
[[Category:Evolution]]
[[Category:Organisms]]

Categories: Animals, Evolution, Organisms