Lynn Margulis was a strong supporter of endosymbiotic theory, the [correct !] notion that mitochondria and chloroplasts originated as independent prokaryotes, first put forth by Konstanin Mereschkowski in the early 1900s. Andreas Schimper had a similar notion as early as 1883.
Margulis went on to theorize that symbiotic relationships between organisms are the dominant driving force of evolution. There certainly are important examples of this: as far as I know, every complex organism that digests cellulose manages it thru a symbiosis with various prokaryotes. Many organisms with a restricted diet have symbiotic bacteria that provide essential nutrients – aphids, for example. Tall fescue, a popular turf grass on golf courses, carries an endosymbiotic fungus. And so on, and on on.
She went on to oppose neodarwinism, particularly rejecting inter-organismal competition (and population genetics itself). From Wiki: [ She also believed that proponents of the standard theory “wallow in their zoological, capitalistic, competitive, cost-benefit interpretation of Darwin – having mistaken him… Neo-Darwinism, which insists on [the slow accrual of mutations by gene-level natural selection], is in a complete funk.” ‘
Symbiotic relationships are important, but they don’t explain nervous systems, or complex methods of reproduction, or livers, or wings. In other words, they certainly are not the dominant driving force of evolution. Mitochondria are important, no doubt about it – but they were incorporated into eukaryotes over a billion years ago. What has endosymbiosis done for us lately?
Margulis was interested in many biological questions , but as far I can see, except for her work on endosymbiosis, she was always wrong. She was wrong in her dabblings with the Gaia hypothesis, wrong in rejecting Carl Woese’s three-domain system, wrong in what she had to say about AIDS research. And, just in case someone somewhere hadn’t noticed that she was a complete nut, she was a 9-11 truther: there was “overwhelming evidence that the three buildings [of the World Trade Center] collapsed by controlled demolition.”
You might think that Lynn Margulis is an example of someone that could think outside the box because she’d never even been able to find it in the first place – but that’s more true of autistic types [like Dirac or Turing], which I doubt she was in any way. I’d say that some traditional prejudices [dislike of capitalism and individual competition], combined with the sort of general looniness that leaves one open to unconventional ideas, drove her in a direction that bore fruit, more or less by coincidence. A successful creative scientist does not have to be right about everything, or indeed about much of anything: they need to contribute at least one new, true, and interesting thing.