Obituary for Professor Thomas Cavalier-Smith FRS, FRSC

The International Society for Evolutionary Protistology has lost one of its most influential members in the field of evolutionary protistology with the passing of Professor Tom Cavalier-Smith, a former Councilor on the ISEP Executive Committee. Tom sadly passed away on the 19th of March 2021, surrounded by his family.

If you asked somebody what they imagine a Professor to look/be like, Tom would probably fit the painted picture perfectly, a bit quirky with a brilliant mind. I have known Tom and interacted with him at conferences since I started out in the field, but as I was not that close to him, I approached Dr Juan Saldarriaga, one of his former PhD students, in the name of ISEP and asked him to write the main obituary for our society. He has kindly agreed and has written an obituary that will also be published in Protist. Juan has beautifully summarized Tom’s scientific being and I am sure Tom would have enjoyed reading it.

Sonja Rueckert (ISEP president)

Conference talks by Tom Cavalier-Smith were always memorable: arrows, colours and unrecognizable words on overhead transparencies already marked during previous talks. A lightning speed delivery, and logical jumps that were seldom followed by an audience that was left behind at the third word and could only stare, mystified, at what was going on at the podium. When time started to run out, delivery speed would increase even more, and used transparencies would start to pile up on the floor behind him. The arrival of Power Point signaled the end of an era: although Tom’s delivery speed remained the same, his talks were now accompanied by slides with phylogenetic trees in tiny, indecipherable fonts and as many arrows as before, and by TEM photographs from obscure organisms that remained unexplained and would lead to all-encompassing hypotheses on the origin of everything. As an audience member, Tom was equally memorable, often quite terrifying for the speaker, although never on purpose. This is because when he had questions, which was often, he would ask them, and his questions tended to be deep and incisive, not the kind that were answered easily. They also were the kind that would ignite furious, passionate debate among different audience members and that on occasion could cause nerf bricks to be thrown from the back of the room towards Tom’s head. He listened to talks all day long, every day, and then read all the posters presented. During these poster sessions Tom was a cherished visitor, because he would engage with any presenter, students new to the field or long-established scientists, in ways that especially young researchers found very reaffirming, commenting extensively on what was being presented and making suggestions that most people found useful. In the evenings Tom could discuss science for hours. In those occasions small groups of people tended to accumulate around him, engaged in lively discussion and enjoying Tom in his element. His arguments were well reasoned and logical, and it took a lot to make him change his views, but when he became convinced that he was wrong he admitted it freely and immediately went on to the next thing. Sometimes changes in his theories came in quick succession and in full view of the audience: during one memorable set of conferences in Australia he modified one of his theories in Melbourne, and then, one week later in Sydney, he modified it again, on stage, scribbling on the Melbourne overhead, based on a question from an audience member and on new data that he had heard about earlier that same day. With him things were very fluid and never personal, it was all about the science and about discovering the secrets of the cells that he cared so much about.

Among biologists in general, Tom Cavalier-Smith will probably be remembered as the modernizer of the large-scale taxonomy of eukaryotes, the inventor of taxon names like the chromists, the rhizarians, the cercozoans and the alveolates, among many, many others. Taxonomists will forever be using the names that he coined, but they would also do well to consider his thoughts on paraphyly, currently an unpopular topic, and should remember, like he always did, that the aim of that branch of biology is to classify organisms that all come from ancestral groups, not only branches in molecular phylogenetic trees. In his early days Tom was a cell biologist working on Chlamydomonas, and later on he became an expert on membranes, flagellar roots, the non-genetic properties of nucleic acids, and the intricacies of endosymbiosis, incidentally a theory that he embraced surprisingly late in his career, but that he later on elaborated at great depth. Cell biology was always close to his heart, and as the shift towards molecular biology happened in the 1990s he insisted on reminding his colleagues to interpret their data in the light of cells as living, physical entities and not just in the abstract.

More generally, Tom Cavalier-Smith will be remembered as the writer of long, dense, prodigious manuscripts impossible to review, dripping with information and with three or four important things per sentence, the sort that necessitate many cups of coffee and one or three weekends in order to be read. This is where Tom shone: his knowledge of protistology and cell biology was extensive, his logic was sound, and he proposed ideas and hypotheses that were intriguing enough to inspire the research programs of many a researcher. He was not always right, but was infuriatingly often so, especially in the apparent absence of any evidence. And here the operating word is “apparent”: his conclusions did not come out of thin air, or of any sort of particularly acute intuition, but of years of obsessively pouring through the old literature and connecting it to newer data, which he looked for and read obsessively. Tom’s main strength was to carefully look at published data and re-interpret them. He would look at old TEM pictures and would discover new membranes around organelles, new intraflagellar helices, or microtubules floating about that he would re-interpret as flagellar roots; then he would use those to produce his hypotheses on cell biology or the evolutionary history of organisms. He also routinely asked for the alignments behind published phylogenetic trees, and if warranted would spend many hours realigning them and coming to his own conclusions, not always the same ones as those from the original authors. As for his own research, he focused on myriads of small, understudied, poorly classified flagellates, heliozoans or amoebae, his favourite kinds of organisms, always helped by Ema, his wife, his companion and his caretaker, the soul of his lab and a cherished co-author of many papers.

As a mentor Tom Cavalier-Smith was engaging, warm and very generous with his time: some of the fondest memories of people who worked with him are long, marathon-like sessions in the cavernous reaches of his office, where papers could pile up literally to the ceiling and where he would expand both on the project at hand and on the world in general while also managing to communicate his unending excitement about the microbial world. One would emerge from these sessions blinking, stunned and exhausted, but most importantly so very excited about the wonders of biology! Tom was quirky and eccentric, and had a quick wit and an infectious, mischievous laughter. Microscopes and binoculars had to go wherever he went: microscopes because he was always sampling in some pond or another (“if you were a flagellate, where would YOU want to live?”), and binoculars because he was a keen bird watcher absolutely in love with nature: he and Ema transformed their small property in Cornwall into a sort of mini nature reserve by planting native trees and shrubs, hoping to restore it to the woodland that it used to be. Tom Cavalier-Smith was without a doubt one of the most important biologists of our time, his influence will be felt for many years to come, and his loss is a devastating one for the field. Rest in peace, Tom, thank you for everything. We promise not to treat your hypotheses as axioms, to do our best to try to poke holes into them, and to modify them extensively as soon as new data become available, just as you would have done yourself. We will miss you, and will remember you often, but especially when we have to establish and name new taxonomic groups ourselves.

Juan Saldarriaga