Back in the 1950s, when Lynn Margulis was a student studying cell biology, there were two scientific theories which were held up for ridicule, to show how far fetched ideas could get if not reigned in by observation, evidence and reason. One was the theory of continental drift – that the earth’s continents somehow floated across the surface of the planet and rearranged themselves over time. The other was the theory of endosymbiosis. The idea that the cells that make up complex things like animals and plants, you and me, somehow originated from a fusion, a symbiosis, of simpler, bacterial cells.
The first theory, continental drift, moved quite swiftly, after that time, from the realm of ridicule to complete mainstream acceptance. Nowadays, it is something that is well known to the general public and I even teach it to primary school kids in grade 3. And they are really interested in it, they love it and they get it. It’s not ridiculous, it’s just the way things are – the land moves, we’re living on this gigantic, slow moving raft. Of course, why not.
The second theory - endosymbiosis - has had a much more difficult and rocky road to traverse from ridicule to what I would call, muted acceptance. It was only by the late 1980s or even after that that it achieved some degree of scientific acceptance, and it has still not reached very far into the public conciousness. Unless you are a biologist you most likely haven’t heard of it and you haven’t heard of Lynn Margulis, it’s tireless advocate over 5 decades. It gets no more than a one paragraph mention in the Victorian Year 12 Biology textbook. Needless to say, I don’t teach it to primary school kids, although I am sure if I did they would love the idea of it.
The reason for this disparity is, I think, that while continental drift was revolutionary it could, quite readily, be incorporated into the prevailing view of the natural history of the earth, and it explained a lot of issues in geology that were a bit of a mystery up till then. Endosymbiosis, on the other hand, was really radical, and it just did not fit in with the existing view of biology and evolution. It still doesn’t really. And there weren’t thought to be any great mysteries in these fields that needed explaining by a new theory. It is still, generally, either ignored or, to my perception anyway, seen by most biologists as an interesting but fairly peripheral idea.
I think this is a pity and something that should change. To some extent, this is because of my own personal view of science and how it interacts with society. I am a science teacher and also a musician and songwriter. And I write songs about scientific ideas that I find interesting and inspiring and this one, to me, has interest and inspiration in spades. It is one of those theories that I would describe as poetic. The songs I write are a kind of science poetry. With ideas like this one though, I don’t have to do much to create the poetry, it’s already there! Two cells fuse to become one. Two bacteia, two individuals, two free living individual selves, fuse to become one, more complex thing.
If you think about it, this can have huge implications on how we see ourselves. Philosophical implications. Implications for our sense of self. Because we are made of the kind of complex cells that I am talking about. And I have to tell you something that you may find strange, you may find disturbing, you may find wonderful, you may even find silly. But it is, in essence true……I have to tell you that you are not quite who you think you are…….You might think of yourself as one whole, singular, individual entity but I have to tell that you are not….In truth you are intrinsically divided…. Divided along very ancient lines. You are actually a colony - a colony of different creatures.
I’m not just talking about the fact that if you include the various things covering your body and inside your intestinal tract and all the other parts of you that are open to the environment, your own cells are outnumbered by about 9 to 1. No, these things crawling in and on you – countless bacteria, viruses, amoebas, worms and mites – you would definitely recognise as foriegners. Intimate foriegners, but foreigners none the less. And although you might not be aware of just how intimate their coexistence is with you – like the tiny mites that live at the base of your eyelashes, eating dead cells and oils that you secrete and coming out at night and crawling all over your body looking for more food - you would probably be right. Although where you finish and they start may be dificult to discern at times. Some of these things just don’t do boundaries very well. They most certainly do not respect personal space. Personal space is simply an opportunity for them to set up camp!
No, I am talking about the cells that make up your body, that you would definitely regard as your own. Well, I’m sorry to say, but they are not completely yours and yours alone. They are actually a mish mash of stuff you have borrowed. Stuff you have borrowed from the bacterial world. Stuff you borrowed and never gave back! If you want, you can think of them as your own. But it’s a bit like that cd you borrowed off a friend years ago and forgot to give it back and now it’s like, well they’ve probably forgotten about it and it’s too late to worry about it, so it feels like it’s really mine, kind of a thing. I’m sorry, it might feel like that cd is yours, but we know it’s really on permanent loan!
This is what the situation is when we consider mitochondria - the little energy powerhouses that are contained within almost every one of the billions of cells that make up your body. These little energy factories were once separate, individual, free living things. They were free living, oxygen respiring bacteria that were ingested by another anaeorobic bacterium that was sort of having trouble coping with all this stuff, oxygen, that was building up in the atmosphere around that time, a billion or so years ago. And instead of digesting it’s meal, the meal became integrated, fused with the devourer. Food became self! Two individual entities became one, to form a new, more complex individual.
We don’t know the exact process by which the fusion occurred. It may be that you are a product of bacterial indigestion. Or the mitochondrial bacteria may have been invaders or parasites of the other cell. However it happened, associations that were once ferocious became benign, invasions turned into a truce.
So in a very real sense you are not a discrete individual entity with a single evolutionary history. Your body is made up of multiple bodies with separate histories. If you were a plant, you would have another, once separate, creature in your cells. The chloroplast. These energy factories that convert sunlight into food were once also separate, squirming little bacteria!
These events are part of the theory of endosymbiosis (meaning symbiosis ‘inside’ the cell). Events that biologists now accept have occurred in the evolution of eukaryotic organisms. That is animals, plants, fungi and protists. All life forms bigger and more complex than bacteria, that contain a nucleus and organelles in their cytoplasm. That they are accepted, is due to the work of one woman – Lynn Margulis. Whether there were other fusions, in addition to these two, is still an issue of argument and debate, but it is also to some extent, still, an issue that is just sort of ignored.
Certainly, knowledge has been growing in recent times about all sorts of interesting symbioses between various organisms. There was one in the news recently. Animals, of course, never obtained chloroplasts. A photosynthesising animal has never evolved. Well, no, actually…at least one has. There is this sea slug that eats algae and incorporates the chloroplasts into its body. This thing looks like a big, green floating leaf. And it doesn’t just get the chloroplasts from the algae, it has incorporated some of the algae’s genes into its own DNA. So this is not just a temporary kind of merger. It is a permanent fusion of two distinct species. Lynn Margulis believes this kind of symbiosis, one that becomes a permanent merger, is actually the major driver of evolutionary change. She calls this symbiogenesis – symbiosis resulting in the formation of new species.
Lynn Margulis is a science hero of mine. She was an amazing, original, insightful, controversial, revolutionary, even heretical scientist. She was also described as stubborn and combatative and someone who would not listen to the arguments of others. She was probably the kind of person Paul Kelly had in mind when he wrote the song ‘Difficult woman’. She died in 2011 at the age of 73 and although she was widely recognised, often rather grudgingly and belatedly recognised, in the field of biology, she is not well known to the general public. She died believing that her belated recognition for endosymbiosis and the origin of mitochondria and chloroplasts was not enough…was no where near enough.
She began as a student in cell biology in the late 1950s. DNA had recently been discovered as the genetic material and everyone knew that genes resided in the nucleus. Margulis, an iconoclast from the start, started looking for DNA in the cytoplasm of cells. No-one had been too interested in this before, they didn’t know if there was any DNA there, and hadn’t thought to ask why there should be any. As far as DNA and genes were concerned the action was in the nucleus. After a few years of looking though, she found evidence of DNA in the chloroplasts of Euglena, a single celled protist similar to the Paramecium you might have studied at school. She was also reading up on the strange ideas of two Russian scientists and one obscure American from decades earlier who had in fact proposed that the organelles of complex cells were the evolutionary result of a symbiosis between bacteria. These ideas had been developed at a time when little was known about the inner workings of the cell and they were unrefined and largely speculative. In the West they were either ignored or, as I said before, ridiculed. Margulis took them seriously, and she started to link them to her research on cytoplasmic DNA. She started to think about origins, the origins of these organelles she was studying. She suggested that the presence of DNA in chloroplasts was due to their evolution from previously free living, photosynthesising cyanobacteria. But she didn’t stop there, she extended the idea of endosymbiosis to mitochondria and other organelles including cilia and flagella.
Her first paper outlining this idea was rejected by 15 scientific journals before being published in the Journal of Theoretical Biology in 1967. It gained her some noteriety, mainly of the ‘isn’t this a cute, funny little idea’ kind. It was not taken seriously by many. Over the next few years she conducted more research, gathered more morphological and DNA evidence, and refined her ideas. She was pregnant at the time, linked in her own symbiosis with her unborn daughter. One individual about to become two. Her perspective broadened, her ideas became bigger. She developed her theory of symbiogenesis – symbiosis resulting in the evolution of new forms of life. Her ideas were radical. In effect, she was rewriting both the history and classification of life on earth. In her view, there are really just two kinds of life – bacteria and everything else. Every visible life form on the planet is just a combination, or community, of bacteria. Life is like a pointilist painting. From far away you see animals and plants and fungi and things. Up close you just see points, which are the bodies of bacteria, only arranged in different ways to create different super-organisms.
She wrote a book outlining her theory. Although she had been contracted by a publisher to write it, the manuscript was rejected when she submitted it due to strident critiques from other scientists. Finally, she got her book - ‘Symbiosis in cell evolution’ - publlished by another company, in 1970. She continued to revise and refine her ideas. Slowly, people began to listen. She argued that in addition to mitochondria and chloroplasts other cellular organelles are also the result of symbiogenesis. According to Margulis, lots of other bits in your cells have also been borrowed from bacteria through a symbiotic merger. For example, the cilia and flagella of eukaryotic cells, and even the wriggling tails of sperm, are the incorporated bodies of various cork screw shaped bacteria known as spirochetes. Other kinds of spirochetes evolved into the internal cellular cytoskeletal structures - microtubules and the centrioles which coordinate cell division. These symbioses, she claimed, were the major events in the evolution of life. The rest was just window dressing.
Eventually, she was proven to be correct about mitochondria and chloroplasts. A ‘smoking gun’ was found for these ancient symbioses. With the advent of DNA sequencing techniques a tell-tale sign emerged showing what happened, and ‘whodunnit’. This sign was uncovered by another scientific iconoclast who thought outside the box. Carl Woese was studying the ancient evolutionary relationships of bacteria. Something no-one thought could really be done. It had all happened too long ago, and had left too little record. But the record is there, in the DNA of mitochondria, chloroplasts and bacteria today. Woese found that if you look at a mitochondria, its DNA is totally different to the DNA of the nucleus of the cell it resides in, but it is very similar to that of a certain kind of oxygen respiring bacteria with a very ancient lineage. Similarly, chloroplast DNA is unlike the nuclear DNA of its present eukaryotic host cell but very like that of certain photosynthesising bacteria. Just as Margulis had postulated. With this result, even her staunchest critics had to agree that she was right. Ok…she was right….about this.
But as for the other stuff…..As far as the cilia and cytoskeletal systems go, there has been no smoking gun found….yet! No DNA has been detected in these structures. Maybe it has been lost over the course of evolution. Maybe it was never there and Margulis is wrong on these points. Her critics, and there are quite a few, argued that she should have been happy to be vindicated about mitochondria and chloroplasts. And so please, now, could she just stop banging on about this other symbiosis stuff. But she would not be quiet, to the end she argued stridently that evolutionary theory, with its focus on random mutation and natural selection as the drivers of adaptation, is missing a huge part of the story of life on earth. In her view it is symbiosis that is central to evolutionary change. Mutation and selection are relatively minor players. It is symbiogenesis that is the primary source of novelty and innovation in evolution. The rest, as she said, is just window dressing.
So why, has symbiosis not been wholeheartedly embraced as an evolutionary mechanism? According to Margulis it is because biologists are simply unwilling to look for it, because they are stuck in a mindset that sees evolution as solely driven by competition and natural selection. In addition, the focus for traditional evolutionary theory has been primarily on animals, and, the last half billion years of earth’s history, while what happened for the 3 billion years before that, and what happened in all the other kinds of living things - plants, fungi, protists and particularly, bacteria - has been relatively ignored. In her view, all the major events in the evolution of life on earth occurred before complex, multicellular animals even appeared, through bacterial mergers. It is bacteria that are responsible for most of the interesting features of life like reproduction, movement and photosynthesis. All the rest was just the icing on the cake! This changes the big picture of evolution. Her picture of of the story of life is not a tree of species forever diverging to form finer and finer distinct twigs, but a web, where the branches merge and fuse together to form new, composite entities. Symbiogenesis is the big, central story of evolution.
This big idea is still resisted by the scientific establishment. This may be because it is wrong. Or it may be because it is too radical and demands too much change of the biological status quo. It would require more than just a few paragraphs in the textbooks about the interesting but supposedly rather marginal origin of mitochondria. It would require this to become part of the main story and lots of other stuff to be added too. It would require the books to be completely rewritten. Whether they ever will, remains to be seen. Time will no doubt eventually reveal the truth. It is my belief, however, that Lynn Margulis’s ideas are not finished with, and will continue to filter provocatively into the world of biological science and into the minds of the general public for decades to come. It may be that my favourite quote of hers turns out to be both correct and prescient. In an interview towards the end of her life, after decades of fighting her critics, clinging stubbornly to her radical ideas, and never backing down, she was asked: ‘Do you ever get tired of being controversial’. Her reply was typical of this great, forthright, combatitive, iconoclastic scientist – “I don’t consider my ideas controversial”….she said ….”I consider them right”.
Favorite Popular Science Books
Bill Bryson A short history of nearly everything
Natalie Angier The Canon
Christopher Potter You are here
David Bodanis The Secret house
Jacob Bronowski The Ascent of Man
Kay Redfield Jamison Exuberance:The passion for life
David Bodanis E=mc2, Electric Universe
Richard Feynman Surely you’re joking, Mr. Feynman?
Bob Berman Strange Universe
Brian Cox and Jeff Forshaw Why does E=mc2? (And why should we care?)
Lewis Thomas Lives of a cell
Rob Dunn Every Living Thing
Richard Dawkins The Blind Watchmaker
Stephen Jay Gould Wonderful Life:The Burgess Shale and the nature of history
Michael Pollan The Botany of Desire
Jane Goodall 50 years at Gombe
Sean B. Carrol Remarkable Creatures
Richard Fortey Earth
Simon Winchester The map that changed the world
Jack Repcheck The man who found time
William Bryant Logan Dirt: The ecstatic skin of the Earth
Peter Ward Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future
Gabrielle Walker Snowball Earth
Oliver Sacks Uncle Tungsten
Theodore Grey Elements
Lauren Redniss Radioactive:Marie and Pierre Curie:A tale of love and fallout