Via Jerry Coyne, I learned that Lynn Margulis died yesterday. Those who’ve seen my public talks will know that most of the time, I refer to famous scientists with an affectionate nickname (never done this in an academic talk. Not yet anyway). Lynn Margulis’s is “the crazy cat lady”. This post will give my opinion of her. I’ll warn you that a lot might seem negative, but I’m not judging her as a person, only her contributions (see the last 2 paragraphs).
Her call to fame is, of course, endosymbiosis, the theory that explains the origins of mitochondria and chloroplasts in eukaryotic cells. I’ll give a short history of the idea before getting to Margulis’s contribution.
Two Russian botanists in the early 20th century, Konstantin Merezhkowsky and Andrei Famintsyn, independently proposed that symbiosis could play a major role in evolution; being in Russia, they were unknown in the West, where Ivan Emmanuel Wallin later also came to the same conclusion based on his discovery that when plant cells divide, the plastids and mitochondria self-replicate separately from the rest of the cell. When he removed the chloroplast from his model organism (Euglena), he found that no new chloroplasts were produced by the plant after cell division. When he added the chloroplast again, they were produced as normal. So he concluded that chloroplasts (and, by extension, the other parts of the cell) are symbiotic organisms, not produced by the cell itself. His 1927 book Symbionticism and the Origin of Species outlines his idea.
It was largely ignored and considered too radical an idea to bother exploring further. It wasn’t until 1967 that a scientist was determined enough to bring it back into biological discourse. That scientist was Lynn Margulis, in her 1967 Journal of Theoretical Biology paper On the origin of mitosing cells (she’s referenced as Sagan (1967), since she was married to the venerable Carl Sagan at the time), in which she outlined her idea that organelles beside the nucleus were bacteria incorporated by symbiosis into the ancestral cell.
This means that eukaryotes are actually supercolonies formed of symbiotic colonies of bacteria coexisting (a triumph of group selection, one might add). The poster children for the theory are mitochondria and chloroplasts, who were once free-living bacteria (purple non-sulphur bacteria and cyanobacteria, respectively) but then eaten and incorporated into their hosts.
We know this as fact now (at least only for mitochondria and chloroplasts), but at the time, she was laughed at and derided for proposing this (she was rejected by 15 journals before being accepted by the Journal of Theoretical Biology), because the evidence was admittedly scant, not to mention that is stank of saltationism, which went against the gradualism espoused by most evolutionary biologists at the time. It wasn’t until the age of common genomics that she was vindicated.
The implications of the theory aren’t just important for cell biologists and people studying the evolutionary history of cells. The most prominent example is the idea and possibility of GMOs, which follows on directly from endosymbiosis – if eukaryotes could incorporate entire foreign bacteria in the wild, why shouldn’t we be able to manufacture them to incorporate a couple of measly foreign genes?
Now here’s the problem with Margulis. I will place a disclaimer here that I don’t know her personally, nor have I ever been a student of hers. All I know is from her writings, both academic and non-academic. As Coyne mentions in his post, especially in her later years, she attacked modern evolutionary biology for ignoring the power of symbiosis. She was one of those who called for a revolution of evolutionary biology. (Note that there is currently a revolution in biology, with a new Modern Synthesis on the way to incorporate the various eco-evo-devo permutations. This is a separate topic.)
Those who do that generally fall into two groups: the overexaggerators of epigenetics, and the overexaggerators of symbiosis. Eva Jablonka is an example of the former; Lynn Margulis of the latter. Basically, she takes it way too far. Among the things she’s proposed since her triumph is that the tails of sperm cells are endosymbiosed spirochaetes, which simply is not true (she also extends it to cilia, the organelles from which sperm tails are derived). And if it were true, we certainly would have found out by now – it’s just a matter of sequencing some genes.
More galling, to me personally, is her sponsoring of this abysmal paper in PNAS, in which Donald Williamson makes up a story that insect larvae are the result of an adult insect fucking a velvet worm. When I first saw it, I thought it was one of those joke papers occasionally published to lighten the mood. But no, it was serious. And the only reason it got published was because Margulis used her power to get it published. The story blew up, because not only did Williamson rape evolutionary biology and arthropodology by not having a single fact in his paper, but also because the way it got published was that Margulis used her power as editor to get it in the publishing queue, because it fit in with her idea that everything evolves by symbiosis. The system is now thankfully abolished. No more freebies.
And that’s her problem: she’s overexaggerated the power of symbiosis. Does it occur in nature? Yes. Did it have an important role in evolution? Of course, depending on the case. But that doesn’t mean that everything is the result of a symbiosis.
This brings up another aspect that interests me in the history of science. Margulis here offers a perfect example of someone who takes an extreme position and never budges. This is very important in the birth of a new theory, and she was right to stick to her guns back in the 1960s and 1970s. It led to her theory being proven correct. But then she took it to more and more extremes.
In other debates in biology, be they big or small, this is the usual pattern. Start with the classical extremist who accepts no change, and the radical extremist who rejects the classical conception. This allows them to present their cases and review all sorts of evidence. And this will show the holes and successes in both positions, and they will gradually soften up and work towards merging the two ideologies to fit the evidence.
In Margulis’s case, she never went through to that second part and always sought to throw out modern evolutionary biology, despite not having enough evidence to justify such an action. She bordered on neo-Lamarckism (which incidentally bears very little resemblance to original Lamarckism), and hated gradualism, preferring to view everything as having evolved by symbiosis-enabled jumps.
Cooperation is a big part of modern evolutionary biology, as is symbiosis in all its forms (from endosymbiosis to parasitism). Punctuated equilibrium is a part of modern evolutionary biology (as part of a spectrum from extreme gradualism to extreme punctuation). And these, as far as anyone can tell, is enough to explain the phenomena we observe, but that she seeks to replace with her theory of symbiosis for everything. I have never understood it.
But anyway, I don’t mean to be so negative. Her theory of endosymbiosis was revolutionary for biology, nobody can deny her that. And it’s true that she did cause us to give a more detailed look at cooperation and symbiosis in general, and their role in evolution. From student friends who were taught by her, I’ve learned that she was a great teacher and that’s something admirable in anyone, especially a working scientist. Sure, she may have been eccentric and extreme in her views (bordering on the dangerous with her HIV denialism), but those are typical double-edged swords. In one aspect, she embodied the perfect scientist: steadfast in her view and willing to go for the evidence, and crazy enough to go against the establishment with new hypotheses. In another way, she was a bit ridiculous with her refusal to consider and properly refute other points of view contradicting her hypotheses.
Whatever your opinion of her, she is worthy of admiration.