Thomas Cavalier-Smith

Thomas Cavalier-Smith
Gonville and Caius College Cambridge , King's College London
Known for	Cavalier-Smith's system of classification of all organisms
Awards	Fellow of the Royal Society (1998) International Prize for Biology (2004) The Linnean Medal (2007) Frink Medal (2007)
Scientific career
Fields	Zoology
Institutions	King's College London, University of British Columbia, University of Oxford
Thesis	Organelle Development in Chlamydomonas reinhardii (1967)
Website	www.zoo.ox.ac.uk/people/view/cavaliersmith_t.htm

Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021^[1]), was a professor of evolutionary biology in the Department of Zoology, at the University 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 the Chromista, Chromalveolata, Opisthokonta, Rhizaria, and Excavata. He was known for his systems of classification of all organisms.

Life and career

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 at

From 1967 to 1969, Cavalier-Smith was a guest investigator at Rockefeller University. He became Lecturer of biophysics at King's College London in 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 the University of British Columbia. In 1999, he joined the University of Oxford, becoming Professor of evolutionary biology in 2000.^[5]

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

Taxonomy

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 to

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 and

) and the resulting classifications, its distinctive character.

Cavalier-Smith's narrative style

Cavalier-Smith was courageous in his adherence to the earlier traditionalist style characterized by

, 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 he will grapple 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

Cavalier-Smith wrote extensively on the taxonomy and classification of all life forms, but especially

, even though it is not widely accepted to be monophyletic (see above).

He also introduced new taxonomic groupings group for eukaryotes such as the

. His taxonomic revisions often influenced the overall classification of all life forms.

Eight kingdoms model

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,

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 kingdom Archezoa to the phylum Amoebozoa.^[25]

Six kingdoms models

By 1998, Cavalier-Smith had reduced the total number of

Five of Cavalier-Smith's kingdoms are classified as

as shown in the following scheme:

• Eubacteria
• Neomura
  • Archaebacteria
  • Eukaryotes
    • Kingdom Protozoa
    • heterotrophs
      )
      • Kingdom Animalia
      • Kingdom Fungi
    • photosynthetic
      )
      • Kingdom Plantae (including red and green algae)
      • Kingdom Chromista

The kingdom Animalia was divided into four subkingdoms:

(all other animal phyla).

He created three new animal phyla:

tardigrades

) and recognised a total of 23 animal phyla.[26]

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

• Unikonts
  • protozoan phylum Amoebozoa (ancestrally uniciliate)
  • opisthokonts
    • uniciliate protozoan phylum Choanozoa
    • kingdom Fungi
    • kingdom
      Animalia
• Bikonts
  • protozoan infrakingdom Rhizaria
    • phylum Cercozoa
    • phylum
      Radiozoa and Foraminifera
      )
  • protozoan infrakingdom Excavata
    • phylum Loukozoa
    • phylum
      Metamonada
    • phylum Euglenozoa
    • phylum Percolozoa
  • protozoan phylum
    Diphylleida
    )
  • the
    chromalveolate
    clade
    • kingdom
      Haptophyta
      )
    • protozoan infrakingdom
      Alveolata
      • phylum
        Ciliophora
      • phylum
        Dinozoa, and Apicomplexa
        )
  • kingdom
    Glaucophyta
    )

Seven kingdoms model

Cavalier-Smith and his collaborators revised the classification in 2015, and published it in

Proposed root of the tree of life

In 2006, Cavalier-Smith proposed that the last universal common ancestor to all life was a non-flagellate Gram-negative bacterium ("negibacterium") with two membranes (also known as diderm bacterium).^[30]

Awards and honours

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

He received the International Prize for Biology from the Emperor of Japan in 2004, and the Linnean Medal for 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 2007 Frink Medal of the Zoological Society of London.^[5]

References

External links

Wikispecies has information related to Thomas Cavalier-Smith.

• "T. Cavalier-Smith". Zoology (Faculty web page). University of Oxford. Archived from the original on 1 May 2008.

• "academic references to "T. Cavalier-Smith"" – via Google Scholar.

• "Thomas Cavalier-Smith" (biography). London, UK:
  The Royal Society
  .