Free Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane
Authors: Nick Lane
hypothesis’. The mainstream view has superseded Lynn Margulis’ original ideas in many details, and in its present form is largely attributable to Oxford biologist Tom Cavalier-Smith. Few researchers have quite as detailed an understanding of the molecular structures of cells and their evolutionary relationships as Cavalier-Smith, and he has put forward numerous important and contentious theories on cellular evolution. The hydrogen hypothesis is an utterly different theory, argued forcefully by Bill Martin, an American biochemist at Heinrich-Heine University in Düsseldorf, Germany. Martin is a geneticist by background, and tends to prefer biochemical, rather than structural, insights into the origins of the eukaryotes. His ideas are counter-intuitive, and have generated a heated, even vitriolic, response in some quarters, but they are underpinned by a crisp ecological logic that cannot be ignored. The pair often clash at conferences, and their views seem to hang over such meetings with an almost Victorian sense of melodrama, reminiscent of Conan Doyle’s ProfessorChallenger. At a splendid discussion meeting on the origin of eukaryotic cells at the Royal Society of London in 2002, Cavalier-Smith and Martin contested each other’s views throughout the meeting, and I was impressed to find them still embroiled in debate hours afterwards in the local pub.
2
Quest for a Progenitor
How did the eukaryotic cell evolve from bacteria? The mainstream view assumes that it was by way of a sequence of tiny steps, through which a bacterium was gradually transformed into a primitive eukaryotic cell, possessing everything that characterises the modern eukaryotes, except for mitochondria. But what were these steps? And how did they get started down a path that in the end found a way across the deep chasm separating the eukaryotes from bacteria?
Tom Cavalier-Smith has argued that the key step forcing the evolution of the eukaryotes was the catastrophic loss of the cell wall. According to the Oxford English Dictionary, the word ‘catastrophe’ means ‘a calamitous fate’ or ‘an event producing a subversion of the order of things’. For any bacteria that lose their cell wall, either definition may easily come true. Most wall-less bacteria are extremely fragile, and unlikely to survive long outside the cosy laboratory environment. This does not mean that such calamities are rare events, though. In the wild, bacterial cell walls might be lost quite often, either by mutation or active sabotage. For example, some antibiotics (such as penicillin) work by blocking the formation of the cell wall. Bacteria engaged in chemical warfare may well have produced such antibiotics. This is not at all improbable—most new antibiotics are isolated from bacteria and fungi engaged in exactly this kind of struggle. So, the first step, the calamitous loss of the cell wall, might not have posed any problem. What of the second step: survival and subversion of the order of things?
As we noted in the previous chapter, there are potentially big advantages to getting rid of the unwieldy cell wall, not least being able to change shape and engulf food whole by phagocytosis. According to Cavalier-Smith, phagocytosis is the defining feature that set the eukaryotes apart from bacteria. Any bacterium that solved the problem of structural support and movement could certainly subvert the established order of things. Yet, for a long time, it looked as if surviving without a cell wall was a magic trick equivalent to pulling a rabbit out of a hat. Bacteria were believed to lack an internal cytoskeleton, and if that was the case, the eukaryotes must have evolved their complex skeleton in a single generation, or faced extinction. In fact this assumption turns out to be groundless. In two seminal papers, published in the journals
Cell
and
Nature
in 2001,Laura Jones and her colleagues at Oxford, and Fusinita van den Ent and her colleagues in Cambridge, showed that some
2
Quest for a Progenitor
How did the eukaryotic cell evolve from bacteria? The mainstream view assumes that it was by way of a sequence of tiny steps, through which a bacterium was gradually transformed into a primitive eukaryotic cell, possessing everything that characterises the modern eukaryotes, except for mitochondria. But what were these steps? And how did they get started down a path that in the end found a way across the deep chasm separating the eukaryotes from bacteria?
Tom Cavalier-Smith has argued that the key step forcing the evolution of the eukaryotes was the catastrophic loss of the cell wall. According to the Oxford English Dictionary, the word ‘catastrophe’ means ‘a calamitous fate’ or ‘an event producing a subversion of the order of things’. For any bacteria that lose their cell wall, either definition may easily come true. Most wall-less bacteria are extremely fragile, and unlikely to survive long outside the cosy laboratory environment. This does not mean that such calamities are rare events, though. In the wild, bacterial cell walls might be lost quite often, either by mutation or active sabotage. For example, some antibiotics (such as penicillin) work by blocking the formation of the cell wall. Bacteria engaged in chemical warfare may well have produced such antibiotics. This is not at all improbable—most new antibiotics are isolated from bacteria and fungi engaged in exactly this kind of struggle. So, the first step, the calamitous loss of the cell wall, might not have posed any problem. What of the second step: survival and subversion of the order of things?
As we noted in the previous chapter, there are potentially big advantages to getting rid of the unwieldy cell wall, not least being able to change shape and engulf food whole by phagocytosis. According to Cavalier-Smith, phagocytosis is the defining feature that set the eukaryotes apart from bacteria. Any bacterium that solved the problem of structural support and movement could certainly subvert the established order of things. Yet, for a long time, it looked as if surviving without a cell wall was a magic trick equivalent to pulling a rabbit out of a hat. Bacteria were believed to lack an internal cytoskeleton, and if that was the case, the eukaryotes must have evolved their complex skeleton in a single generation, or faced extinction. In fact this assumption turns out to be groundless. In two seminal papers, published in the journals
Cell
and
Nature
in 2001,Laura Jones and her colleagues at Oxford, and Fusinita van den Ent and her colleagues in Cambridge, showed that some