(8 pm. – promoted by ek hornbeck)
Lynn Margulis is best known for postulating in 1966 the theory of endosymbiosis, the theory that eukaryotic cells (having nuclear DNA and nucleically differentiated organelles) resulted from the symbiotic fusion of smaller and more primitive prokaryotic cells. Both mitochondria and chloroplasts, critical metabolic organelles in animal and plant eukaryotic cells, for example, are thought to be descended from independent prokaryotic lineages. While her hypothesis was roundly rejected the over the first 15 or so submissions, the theory of endosymbiosis is now one of the most important ideas advanced in evolutionary biology in the last century. As Richard Dawkins put it:
I greatly admire Lynn Margulis’s sheer courage and stamina in sticking by the endosymbiosis theory, and carrying it through from being an unorthodoxy to an orthodoxy. I’m referring to the theory that the eukaryotic cell is a symbiotic union of primitive prokaryotic cells. This is one of the great achievements of twentieth-century evolutionary biology, and I greatly admire her for it.
While I cannot do justice to the topic, several things do stand out to even a blockhead like me.
The rise of eukaryotic organization was a massive evolutionary event, perhaps second or third only to replication (from my anthropomorphic perspective). Prior to eukaryotes, the release of oxygen from photosynthetic prokaryotic critters (such as cyanobacteria blue-green algae) into the biosphere was a planet-changing event, creating an entirely new, massive selection pressure (an oxygen-rich atmosphere) on evolutionary diversity, resulting in aerobic metabolism by mitochondrion-like cell primitives.
The mitochondrion-like oxidizing metabolizers were engulfed by other organisms, allowing the engulfing organism to reap the benefits of oxidative metabolism from their engulfed guests acting as power stations. Similarly, photosynthetic chloroplasts in plants are thought to have originated as a distinct lineage from blue-green algae. Possibly, various independent prokaryotes living in colonies for sundry efficiencies of group co-habitation, e.g., similar to the benefits of having one’s own intestinal flora to aid digestion, led to functional fusion and specialization between cell lineages, and ultimately a larger more complex eukaryotic cell.
However the symbiotic merging of separate lineages occurred precisely, increased complexity and functional specializations in eurkaryotic cells gave rise to multi-cellular organisms, cell differentiation and complex developmental timetables, making possible all fish, flesh, and fowl, not to mention invertebrates, fungi, plants, and a fascinating array of singled-celled protozoans.
We humans have over 200 cell types in the human body (skin cells, liver cells, pancreatic cells, muscle cells, etc). Among countless innovations, the internalization of oxidative metabolism in mitochondria freed cell membranes to carry out complex signaling functions, such as neuronal signaling, as is sometimes reported to occur in grey matter of the human squash. Thinking and consciousness, as we know it, were made possible by endosymbiosis, the engulfing of and subsequent fusion with another organism for mutual benefit.
One can think of the endosymbiosis of independent life forms (especially the power-plants, such as mitochondria and chloroplasts) by their symbionts as something like the fabled midichlorians of Star Wars teeming in the cells of other living things, and most strongly in those best harnessing the esoteric ways of “the force.” Apparently, George Lucas literally, loosely based his midichlorians on mitochondria. It tells you something important when good scientists are better story-tellers than Hollywood big shots.
It’s worth noting that the theory of endosymbiosis (plus selection) also stands in stark contrast to Darwinian random genetic mutation (plus selection). Professor Margulis generated friction for decades after her proposal, as evolution through symbiotic fusion between separate lineages is entirely distinct from genetic mutation within a lineage. The prevailing dogma buckled when mitochondria and chloroplasts were shown to carry their own DNA independent of nuclear DNA. As Dawkins said, symbiotic theory is now orthodoxy, occupying the critical opening discussion concerning cell evolution in the widely used and authoritative textbook The Cell. Symbiosis turns out to have been an incalculable force in the radiation of life and biodiversity, and the theory remains an awesome contribution to our understanding.
Margulis was elected to the National Academy of Sciences and received the National Medal of Science, the Da Vinci Medallion, and the prestigious Darwin-Wallace Medal (awarded every 50 years), among other distinctions. She also co-authored popular books with her son, Dorion Sagan (son of first husband, cosmologist Carl Sagan), and is survived by other accomplished offspring, as well. Men-folk can never claim the distinction of bearing children in mid-career.
I cannot resist adding that as prominent female scientist who led with her chin against prevailing orthodoxies, Margulis maintained the courage of her convictions and scientific integrity when few others dared. Her blunt assessment of 9/11 should mortify more reticent scientists for their failure to be candid, for failing to lead that discussion on scientific merits. Where others shrank, Lynn Margulis stood tall. She explains the importance of scientific accountability that is available to everyone in the video below: