Before I became a full-time writer, I worked as a scientist and university lecturer. Most of my research investigated the symbiotic relationships between animals and single-celled algae: how the sizes of populations of algae within animal cells were regulated, movement of photosynthetically-fixed carbon from algae to host animal, movement of ammonium and amino acids from host animal to algae, and so on. My chief research organism was green hydra, a common freshwater polyp that conveniently reproduces asexually by budding off new animals, so that uniform cloned populations can be grown in the laboratory (the image at the head of this piece is of a single green hydra digestive cell, with its population of symbiotic Chlorella algae clustered at the base of the cell), but I also worked on sea anemones and reef-forming corals.
I'm reminded of this by news of the death of Professor Lynn Margulis, who was one of the prominent workers in the symbiosis field. She was a friend and research associate of my Ph.D supervisor, Professor Sir David Smith, and I met her not only when she visited his labs, but at conferences in the UK and abroad. She was always a whirlwind of energy, promoting her ideas and probing everyone else's with intense acuity. She had forged a career at a time when women were in a minority in the sciences, and for years championed the highly unfashionable idea that mitochondria (the energy-generating organelles found in almost every cell of eukaryotic organisms) and plant chloroplasts (the organelles where photosynthesis takes place) had once been independent organisms that had established a symbiotic relationship with the ancestors of animals and of plants. This theory of symbiogenesis had been first advanced by K. S. Mereschkovsky and Ivan Wallin in the 1920s, but had passed into obscurity. Lynn Margulis dusted it down and supported it with evidence that pointed to the residual bacterial characteristics of the two types of organelles, and their possession of small amounts of DNA. That the symbiotic origin of both mitochondria and chloroplasts is now widely accepted is due almost entirely to Lynn Margulis's dogged and tireless work.
She advanced the idea that flagellae in animal cells were the remnants of bacterial symbionts with rather less success (one problem is that the whip-like flagellae don't possess any DNA), and her efforts to expand the idea that the central driver of evolution was symbiotic acquisition of new DNA rather than mutation of nuclear DNA likewise has not meet with much success. But she was also an early promotor of James Lovelock's Gaia hypothesis, published papers in the then unfashionable field of exobiology, and her symbiogenesis theory is a cornerstone of the idea that symbiosis and other forms of cooperation have made important contributions to the evolution of life on Earth. I admired her hugely. Ava atque vale.