Aristotle

==== Classification of living things ====

{{further|Scala naturae}}

[[File:Scyliorhinus retifer embryo.JPG|thumb |Aristotle recorded that the [[embryo]] of [[Mustelus canis|<!--a different species shown-->a dogfish]] was attached by a cord to a kind of placenta (the [[yolk sac]]), like a higher animal; this formed an exception to the linear scale from highest to lowest.{{sfn|Leroi|2015|pages=72–74}}]]

Aristotle distinguished about 500 species of [[animal]]s,{{sfn|Bergstrom|Dugatkin|2012|page=35}}{{sfn|Rhodes|1974|page=7}} arranging these in the ''History of Animals'' in a graded scale of perfection, a nonreligious version of the ''[[scala naturae]]'', with man at the top. His system had eleven grades of animal, from highest potential to lowest, expressed in their form at birth: the highest gave [[viviparity|live birth]] to hot and wet creatures, the lowest laid cold, dry mineral-like eggs. Animals came above [[plant]]s, and these in turn were above minerals.{{sfn|Mayr|1982|pages=201–202}}{{sfn|Lovejoy|1976}} He grouped what the modern zoologist would call [[vertebrate]]s as the hotter "animals with blood", and below them the colder [[invertebrate]]s as "animals without blood". Those with blood were divided into the live-bearing ([[mammal]]s), and the egg-laying ([[bird]]s, [[reptile]]s, [[fish]]). Those without blood were insects, crustacea (non-shelled – cephalopods, and [[crustacea|shelled]]) and the hard-shelled [[mollusc]]s ([[bivalve]]s and [[gastropod]]s). He recognised that animals did not exactly fit into a linear scale, and noted various exceptions, such as that sharks had a [[placenta]] like the tetrapods. To a modern biologist, the explanation, not available to Aristotle,<!--Leroi |p= 113--> is [[convergent evolution]].{{sfn|Leroi|2015|pages=111–119}} Philosophers of science have generally concluded that Aristotle was not interested in taxonomy,<ref>{{cite book |last=Lennox |first=James G. |title=Aristotle's Philosophy of Biology: Studies in the Origins of Life Science |date=2001 |publisher=[[Cambridge University Press]] |location=Cambridge |isbn=0-521-65976-0 |pages=346}}</ref><ref>{{cite journal |last1=Sandford |first1=Stella |title=From Aristotle to Contemporary Biological Classification: What Kind of Category is "Sex"? |journal=Redescriptions: Political Thought, Conceptual History and Feminist Theory |date=3 December 2019 |volume=22 |issue=1 |pages=4–17 |doi=10.33134/rds.314 |s2cid=210140121 |language=en |issn=2308-0914|doi-access=free }}</ref> but zoologists who studied this question in the early 21st century think otherwise.<ref>{{cite journal |last1=Voultsiadou |first1=Eleni |last2=Vafidis |first2=Dimitris |title=Marine invertebrate diversity in Aristotle's zoology |journal=Contributions to Zoology |date=1 January 2007 |volume=76 |issue=2 |pages=103–120 |doi=10.1163/18759866-07602004 |s2cid=55152069 |url=https://doi.org/10.1163/18759866-07602004 |language=en |issn=1875-9866}}</ref><ref>{{cite journal |last1=von Lieven |first1=Alexander Fürst |last2=Humar |first2=Marcel |title=A Cladistic Analysis of Aristotle's Animal Groups in the "Historia animalium" |journal=History and Philosophy of the Life Sciences |date=2008 |volume=30 |issue=2 |pages=227–262 |jstor=23334371 |pmid=19203017 |url=https://www.jstor.org/stable/23334371 |issn=0391-9714}}</ref><ref>{{cite journal |last1=Laurin |first1=Michel |last2=Humar |first2=Marcel |title=Phylogenetic signal in characters from Aristotle's History of Animals |journal=Comptes Rendus Palevol |date=2022 |volume=21 |issue=1 |pages=1–16 |doi=10.5852/cr-palevol2022v21a1 |s2cid=245863171 |language=fr|doi-access=free }}</ref> He believed that purposive final causes guided all natural processes; this [[teleological]] view justified his observed data as an expression of formal design.{{sfn|Mason|1979|pp=43–44}}

{|class="wikitable" style="font-size: 80%;"
|+ Aristotle's ''[[Scala naturae]]'' (highest to lowest)
! Group !! Examples<br/>(given by Aristotle) !! Blood !! Legs !! Souls<br/>(Rational,<br/>Sensitive,<br/>Vegetative) !! Qualities<br/>({{font color|red|Hot}}–{{font color|blue|Cold}},<br/>{{font color|green|Wet}}–{{font color|brown|Dry}})
|-
|Man||Man||with&nbsp;blood||2 legs||R, S, V||{{font color|red|Hot}}, {{font color|green|Wet}}
|-
|[[Mammal|Live-bearing tetrapods]]||Cat, [[hare]]||with&nbsp;blood||4 legs||S, V||{{font color|red|Hot}}, {{font color|green|Wet}}
|-
|[[Cetaceans]]||[[Dolphin]], [[whale]]||with&nbsp;blood||none||S, V||{{font color|red|Hot}}, {{font color|green|Wet}}
|-
|[[Birds]]||[[Bee-eater]], [[nightjar]]||with&nbsp;blood||2 legs||S, V||{{font color|red|Hot}}, {{font color|green|Wet}}, except {{font color|brown|Dry}} eggs
|-
|[[Reptile|Egg-laying tetrapods]]||[[Chameleon]], [[crocodile]]||with&nbsp;blood||4 legs||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}} except scales, eggs
|-
|[[Snakes]]||Water snake, [[Ottoman viper]]||with&nbsp;blood||none||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}} except scales, eggs
|-
|Egg-laying [[fish]]es||[[Sea bass]], [[Sparisoma cretense|parrotfish]]||with&nbsp;blood||none||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}}, including eggs
|-
|(Among the egg-laying fishes):<br />placental [[selachian]]s||[[Shark]], [[Skate (fish)|skate]]||with&nbsp;blood||none||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}}, but [[placenta]] like tetrapods
|-
|[[Crustaceans]]||[[Shrimp]], [[crab]]||without||many legs||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}} except shell
|-
|[[Cephalopods]]||[[Squid]], [[octopus]]||without||tentacles||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}}
|-
|[[Mollusc|Hard-shelled animals]]||[[Cockle (bivalve)|Cockle]], [[Charonia variegata|trumpet snail]]||without||none||S, V||{{font color|blue|Cold}}, {{font color|brown|Dry}} (mineral shell)
|-
|Larva-bearing insects||[[Ant]], [[cicada]]||without||6 legs||S, V||{{font color|blue|Cold}}, {{font color|brown|Dry}}
|-
|[[Spontaneous generation|Spontaneously generating]]||[[Sponges]], [[worm]]s||without||none||S, V||{{font color|blue|Cold}}, {{font color|green|Wet}} or {{font color|brown|Dry}}, from earth
|-
|[[Plants]]||[[Common fig|Fig]]||without||none||V||{{font color|blue|Cold}}, {{font color|brown|Dry}}
|-
|[[Mineral]]s||Iron||without||none||none||{{font color|blue|Cold}}, {{font color|brown|Dry}}
|}