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Thomas Cavalier-Smith

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Thomas Cavalier-Smith
Born(1942-10-21)21 October 1942
London, United Kingdom
Died19 March 2021(2021-03-19)(aged 78)
NationalityBritish
Alma materGonville and Caius CollegeCambridge, King's College London
Known forCavalier-Smith's system of classification of all organisms
AwardsFellow of the Royal Society(1998)
International Prize for Biology(2004)
TheLinnean Medal(2007)
Frink Medal(2007)
Scientific career
FieldsZoology
InstitutionsKing's College London,University of British Columbia,University of Oxford
ThesisOrganelle Development inChlamydomonas reinhardii(1967)
Websitewww.zoo.ox.ac.uk/people/view/cavaliersmith_t.htm

Thomas(Tom)Cavalier-Smith,FRS,FRSC,NERCProfessorial Fellow (21 October 1942 – 19 March 2021[1]), was a professor ofevolutionary biologyin the Department of Zoology, at theUniversity of Oxford.[2]

His research has led to discovery of a number of unicellular organisms (protists) and advocated for a variety of major taxonomic groups, such as theChromista,Chromalveolata,Opisthokonta,Rhizaria,andExcavata.He was known forhis systems of classification of all organisms.

Life and career

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Cavalier-Smith was born on 21 October 1942 in London. His parents were Mary Maude (née Bratt) and Alan Hailes Spencer Cavalier Smith.[3]

He was educated atNorwich School,Gonville and Caius College, Cambridge(MA) in Biology andKing's College London(PhD) in Zoology. He was under the supervision ofSir John Randallfor his PhD thesis between 1964 and 1967; his thesis was entitled "Organelle Development inChlamydomonas reinhardii ".[4]

From 1967 to 1969, Cavalier-Smith was a guest investigator atRockefeller University.He became Lecturer of biophysics atKing's College Londonin 1969. He was promoted to Reader in 1982. From the early 1980s, Smith promoted views about the taxonomic relationships among living organisms. He was prolific, drawing on a near-unparalleled wealth of information to suggest novel relationships. In 1989 he was appointed Professor of Botany at theUniversity of British Columbia. In 1999, he joined theUniversity of Oxford,becoming Professor of evolutionary biology in 2000.[5]

Thomas Cavalier-Smith died in March 2021 following the development of cancer.

Taxonomy

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Cavalier-Smith was a prolific taxonomist, drawing on a near-unparalleled wealth of information to suggest novel relationships. His suggestions were translated into taxonomic concepts and classifications with which he associated new names, or in some cases, reused old names. Cavalier-Smith did not follow or espouse an explicit taxonomic philosophy but his approach was closest to evolutionary taxonomy. He and several other colleagues were opposed tocladisticapproaches to taxonomy arguing that the goals of cladification and classification were different;[6]his approach was similar to that of many others' broad-based treatments of protists.[7][8]

The scope of Cavalier-Smith's taxonomic propositions was grand, but the numbers and composition of the components (taxa), and, often, their relations were not stable. Propositions were often ambiguous and short-lived; he frequently amended taxa without any change in the name. His approach was not universally accepted: Others attempted to underpin taxonomy of protists with a nested series of atomised, falsifiable propositions, following the philosophy of transformed cladistics.[9]However, this approach is no longer considered defensible.[10]

Cavalier-Smith's ideas that led to the taxonomic structures were usually first presented in the form of tables andcomplex, annotated diagrams.When presented at scientific meetings, they were sometimes too rich, and often written too small, for the ideas to be easily grasped. Some such diagrams made their way into publications, where careful scrutiny was possible, and where the conjectural nature of some assertions was evident. The richness of his ideas, their continuing evolution, and the transition into taxonomies that gave Cavalier-Smith's investigations into evolutionary paths (phylogeny) and the resulting classifications, its distinctive character.

Cavalier-Smith's narrative style

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Cavalier-Smith was courageous in his adherence to the earlier traditionalist style characterized byCharles Darwin,that of relying on narratives. One example was his advocacy for theChromistathat united lineages that had plastids with chlorophylls a and c (primarily chrysophytes and otherstramenopiles,cryptophytes, and haptophytes) despite clear evidence that the group corresponded to a clade.

It was Cavalier-Smith's claim that there was a single endosymbiotic event by which chlorophyll a c containing plastids were acquired by a common ancestor of all three groups, and that the differences (such as cytological components and their arrangements) among the groups were the result of subsequent evolutionary changes. This interpretation that chromists were monophyletic also required that the heterotrophic (protozoan) members of all three groups had arisen from ancestors with plastids.

The alternative hypothesis was that the three chromophytic lineages were not closely related (to the exclusion of other lineages) (i.e. were polyphyletic), likely that all were ancestrally without plastids, and that separate symbiotic events established the chlorophyll a/c plastids stramenopiles, cryptomonads and haptophytes. The polyphyly of the chromists has been re-asserted in subsequent studies.[11]

Cavalier-Smith's lack of an objective and reproducible methodology that would translate evolutionary insights into taxa and hierarchical schemes, were often confusing to those who did not follow his publications closely. Many of his taxa requiring his frequent adjustment, as illustrated below. In turn this led to confusion as to the scope of taxa a taxonomic name was applied to.

Cavalier-Smith also reused familiar names (such as Protozoa) for innovative taxonomic concepts. This created confusion because Protozoa was and still is used in its old sense,[12]alongside its use in the newer senses. Because of Cavalier-Smith's tendency to publish rapidly and to change his narratives and taxonomic summaries frequently, his approach and claims were frequently debated.

Palaeos.com described his writing style as follows:

Prof. Cavalier-Smith of Oxford University has produced a large body of work which is well regarded. Still, he is controversial in a way that is a bit difficult to describe. The issue may be one of writing style. Cavalier-Smith has a tendency to make pronouncements where others would use declarative sentences, to use declarative sentences where others would express an opinion, and to express opinions where angels would fear to tread. In addition, he can sound arrogant, reactionary, and even perverse. On the other [hand], he has a long history of being right when everyone else was wrong. To our way of thinking, all of this is overshadowed by one incomparable virtue: the fact that hewillgrapple with the details. This makes for very long, very complex papers and causes all manner of dark murmuring, tearing of hair, and gnashing of teeth among those tasked with trying to explain his views of early life. See, [for example], Zrzavý (2001)[13][and] Patterson (1999).[14][15][16]Nevertheless, he deals with all of the relevant facts.[17]

Cavalier-Smith's contributions

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Main articles:Cavalier-Smith's system of classificationandKingdom (biology)

Tree of life and major steps in cell evolution after Cavalier-Smith,c. 2010,before his 2015 revision.

Cavalier-Smith wrote extensively on the taxonomy and classification of all life forms, but especiallyprotists.One of his major contributions to biology was his proposal of a newkingdomof life: theChromista,even though it is not widely accepted to be monophyletic (see above).

He also introduced new taxonomic groupings group for eukaryotes such as theChromalveolata(1981),Opisthokonta(1987),Rhizaria(2002), andExcavata(2002). Though well known, many of his claims have been controversial and have not gained widespread acceptance in thescientific community.His taxonomic revisions often influenced the overall classification of all life forms.

Eight kingdoms model

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Cavalier-Smith's first major classification system was the division of all organisms into eight kingdoms. In 1981, he proposed that by completely revising Robert Whittaker's Five Kingdom system, there could be eight kingdoms: Bacteria, Eufungi, Ciliofungi, Animalia, Biliphyta, Viridiplantae, Cryptophyta, and Euglenozoa.[18]

In 1983, he revised his system particularly in the light of growing evidence that Archaebacteria were a separate group from Bacteria,[19]to include an array of lineages that had been excluded from his 1981 treatment, to deal with issues of polyphyly, and to promote new ideas of relationships. In addition, some protists lacking mitochondria were discovered.[20]As mitochondria were known to be the result of theendosymbiosisof aproteobacterium,it was thought that these amitochondriate eukaryotes were primitively so, marking an important step ineukaryogenesis.As a result, these amitochondriate protists were given special status as a protozan subkingdomArchezoa,that he later elevated to kingdom status.[20]This was later referred to as theArchezoa hypothesis.[21]In 1993, the eight kingdoms became: Eubacteria, Archaebacteria, Archezoa, Protozoa, Chromista, Plantae, Fungi, and Animalia.[22]

The kingdom Archezoa went through many compositional changes due to evidence of polyphyly and paraphyly before being abandoned.[23][24]He assigned some former members of the kingdomArchezoato the phylumAmoebozoa.[25]

Six kingdoms models

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By 1998, Cavalier-Smith had reduced the total number ofkingdomsfrom eight to six:Animalia,Protozoa,Fungi,Plantae(including Glaucophyte,redandgreen algae),Chromista,and Bacteria.[26]Nevertheless, he had already presented this simplified scheme for the first time on his 1981 paper[18]and endorsed it in 1983.[27]

Table 11 From Eukaryote kingdoms: seven or nine?

Five of Cavalier-Smith's kingdoms are classified aseukaryotesas shown in the following scheme:

The kingdom Animalia was divided into four subkingdoms:Radiata(phylaPorifera,Cnidaria,Placozoa,andCtenophora),Myxozoa,Mesozoa,andBilateria(all other animal phyla).

He created three new animal phyla:Acanthognatha(rotifers,acanthocephalans,gastrotrichs,andgnathostomulids),Brachiozoa(brachiopodsandphoronids), andLobopoda(onychophoransandtardigrades) and recognised a total of 23 animal phyla.[26]

Cavalier-Smith's 2003 classification scheme:[28]

Seven kingdoms model

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Cavalier-Smith and his collaborators revised the classification in 2015, and published it inPLOS ONE.In this scheme they reintroduced the division of prokaryotes into two kingdoms, Bacteria (previously 'Eubacteria') and Archaea (previously 'Archebacteria'). This is based on the consensus in theTaxonomic Outline of Bacteria and Archaea(TOBA) and theCatalogue of Life.[29]

Proposed root of the tree of life

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In 2006, Cavalier-Smith proposed that thelast universal common ancestorto all life was anon-flagellateGram-negative bacterium( "negibacterium" ) with twomembranes(also known asdiderm bacterium).[30]

Awards and honours

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Cavalier-Smith was elected Fellow of theLinnean Society of London(FLS) in 1980, theInstitute of Biology(FIBiol) in 1983, theRoyal Society of Arts(FRSA) in 1987, theCanadian Institute for Advanced Research(CIFAR) in 1988, theRoyal Society of Canada(FRSC) in 1997, and theRoyal Society of London(FRS) in 1998.[31]

He received theInternational Prize for Biologyfrom the Emperor of Japan in 2004, and theLinnean Medalfor Zoology in 2007. He was appointed Fellow of the Canadian Institute for Advanced Research (CIFAR) between 1998 and 2007, and Advisor of the Integrated Microbial Biodiversity of CIFAR.[32]He won the 2007Frink Medalof theZoological Society of London.[5]

References

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  1. ^Saldarriaga, Juan F. (2021). "Thomas Cavalier-Smith (October 21, 1942 – March 19, 2021)".Protist(Obituary).172(3): 125807.doi:10.1016/j.protis.2021.125807.S2CID235321431.
  2. ^"Professor Dr. Tom Cavalier-Smith, FRS, FRSC, Professor of Evolutionary Biology and NERC Professorial Fellow in the Department of Zoology, Oxford University".Cavali.Archived fromthe originalon 4 March 2016.Retrieved11 February2016.
  3. ^Marriage of Alan C. Smith and Mary Maud Bratt, 1st Qtr 1942, Wayland Reg Dist. (GRO Ref 4b/743). Birth of Thomas C Smith (mother's maiden name Bratt) last Qtr 1942, Greenwich Reg Dist. (GRO Ref 1d/650). Source www.freebmd.org.uk.
  4. ^Cavalier-Smith, Thomas (1967).Organelle development inChlamydomonas reinhardii(PhD thesis thesis).University of London.OCLC731219097.
  5. ^ab"Thomas (Tom) CAVALIER-SMITH".Debrett's. Archived fromthe originalon 15 March 2016.Retrieved11 February2016.
  6. ^Ruggiero, Michael A.; Gordon, Dennis P.; Orrell, Thomas M.; Bailly, Nicolas; Bourgoin, Thierry; Brusca, Richard C.; Cavalier-Smith, Thomas; Guiry, Michael D.; Kirk, Paul M. (29 April 2015). Thuesen, Erik V. (ed.)."A Higher Level Classification of All Living Organisms".PLOS ONE.10(4): e0119248.Bibcode:2015PLoSO..1019248R.doi:10.1371/journal.pone.0119248.ISSN1932-6203.PMC4418965.PMID25923521.
  7. ^Margulis, L.;McKhann, H.I.; Olendzenski, L., eds. (1993).Illustrated Glossary of Protoctista: Vocabulary of the Algae, Apicomplexa, Ciliates, Foraminifera, Microspora, Water Molds, Slime Molds, and the other Protoctists.Jones and Bartlett.
  8. ^Margulis, Lynn; Schwartz, Karlene V., eds. (1997).Five Kingdoms: An illustrated guide to the phyla of life on Earth.W.H. Freeman & Company.ISBN0-613-92338-3.
  9. ^Patterson, D.J. (1985). "The fine structure of Opalina ranarum (family Opalinidae): Opalinid phylogeny and classification".Protistologica.21:413–428.
  10. ^Rieppel, Olivier (2008)."Hypothetico-deductivism in systematics: fact or fiction?".Papéis Avulsos de Zoologia.48(23): 263–273.doi:10.1590/S0031-10492008002300001.ISSN1807-0205.
  11. ^Burki, F.; Roger, A.J.; Brown, M.W.; Simpson, A.G.B. (2020)."The new tree of eukaryotes".Trends in Ecology and Evolution.35(1): 43–55.doi:10.1016/j.tree.2019.08.008.PMID31606140.S2CID204545629.
  12. ^el-Bawab, F. (2020). "Chapter 3 – Phylum Protozoa".Invertebrate Embryology and Reproduction.Academic Press. pp. 68–102.doi:10.1016/B978-0-12-814114-4.00003-5.S2CID240900596.
  13. ^Zrzavý, J (2001)."The interrelationships of metazoan parasites: A review of phylum-and higher-level hypotheses from recent morphological and molecular phylogenetic analyses".Folia Parasitologica.48(2): 81–103.doi:10.14411/fp.2001.013.PMID11437135.
  14. ^Patterson, David J. (1999). "The Diversity of Eukaryotes".The American Naturalist.154(S4): S96–S124.doi:10.1086/303287.PMID10527921.S2CID4367158.
  15. ^"Apusomonadida".Archived fromthe originalon 7 September 2008.Retrieved11 February2016.
  16. ^EukaryaArchived2010-12-20 at theWayback Machine.
  17. ^ "Origins of the Eukarya".Archived fromthe originalon 20 December 2010.Retrieved9 February2009.
  18. ^abCavalier-Smith, T. (1981). "Eukaryote kingdoms: Seven or nine?".Biosystems.14(3–4): 461–481.doi:10.1016/0303-2647(81)90050-2.PMID7337818.
  19. ^Cavalier-Smith, Thomas (1983). "A 6-kingdom classification and a unified phylogeny".Endocytobiology II:1027–1034.
  20. ^abCavalier-Smith, Thomas (1987). "Eukaryotes with no mitochondria".Nature.326(6111): 332–333.Bibcode:1987Natur.326..332C.doi:10.1038/326332a0.PMID3561476.S2CID4351363.
  21. ^Roger, Andrew J. (1999)."Reconstructing Early Events in Eukaryotic Evolution".The American Naturalist.154(S4): S146–S163.doi:10.1086/303290.ISSN0003-0147.PMID10527924.S2CID32138852.
  22. ^Cavalier-Smith, T. (1993)."Kingdom protozoa and its 18 phyla".Microbiological Reviews.57(4): 953–994.doi:10.1128/mmbr.57.4.953-994.1993.PMC372943.PMID8302218.
  23. ^Cavalier-Smith, T.; Chao, E.E. (1996). "Molecular phylogeny of the free-living archezoanTrepomonas agilisand the nature of the first eukaryote ".Journal of Molecular Evolution.43(6): 551–562.Bibcode:1996JMolE..43..551C.doi:10.1007/BF02202103.PMID8995052.S2CID28992966.
  24. ^Simpson, A.G.B.; Bernard, C.; Fenchel, T.; Patterson D.J. (1997). "The organisation ofMastigamoeba schizophrenian. sp.: More evidence of ultrastructural idiosyncrasy and simplicity in pelobiont protists ".European Journal of Protistology.33:87–98.doi:10.1016/S0932-4739(97)80024-7.
  25. ^Cavalier-Smith, T. (2004)."Only six kingdoms of life".Proceedings of the Royal Society B: Biological Sciences.271(1545): 1251–62.doi:10.1098/rspb.2004.2705.PMC1691724.PMID15306349.
  26. ^abCavalier-Smith, T. (2007). "A revised six-kingdom system of life".Biological Reviews.73(3): 203–266.doi:10.1111/j.1469-185X.1998.tb00030.x.PMID9809012.S2CID6557779.
  27. ^Cavalier-Smith, T. (1983). "A 6-Klngdom Classification and a Unified Phylogeny". In Schenk, H.E.A.; Schwemmler, W.S. (eds.).A 6-kingdom classification and a unified phylogeny.Endocytobiology II: Intracellular Space as Oligogenetic. Berlin, DE: Walter de Gruyter & Co. pp. 1027–1034.doi:10.1515/9783110841237-104.ISBN9783110841237.
  28. ^Cavalier-Smith, Thomas (2003). "Protist phylogeny and the high-level classification of Protozoa".European Journal of Protistology.39(4): 338–348.doi:10.1078/0932-4739-00002.
  29. ^Ruggiero, Michael A.; Gordon, Dennis P.; Orrell, Thomas M.; Bailly, Nicolas; Bourgoin, Thierry; Brusca, Richard C.; Cavalier-Smith, Thomas; Guiry, Michael D.; Kirk, Paul M.; Thuesen, Erik V. (2015)."A higher level classification of all living organisms".PLOS ONE.10(4): e0119248.Bibcode:2015PLoSO..1019248R.doi:10.1371/journal.pone.0119248.PMC4418965.PMID25923521.
  30. ^Cavalier-Smith, Thomas (2006)."Rooting the tree of life by transition analyses".Biology Direct.1:19.doi:10.1186/1745-6150-1-19.PMC1586193.PMID16834776.
  31. ^"Awards and distinctions".Cavali. Archived fromthe originalon 23 July 2016.Retrieved11 February2016.
  32. ^"Thomas Cavalier-Smith".Canadian Institute for Advanced Research.Retrieved11 February2016.
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