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Not quite symbiosis

Way back in 1964, when I was working in Boston with a very high-powered team of developers working on elementary science curriculum, I was absolutely surrounded by brilliant people.

Way back in 1964, when I was working in Boston with a very high-powered team of developers working on elementary science curriculum, I was absolutely surrounded by brilliant people. There was one very penetrating and definite voice in particular, that drifted over the temporary partitions into our zone.
It belonged to a professor from Boston University. Though Lynn Margulis was only 26 years old, she had already been married to scientist and science popularizer, Carl Sagan and had two kids with him. Divorced, she was living with her new husband, the easy going and likeable Tom Margulis. He was also working with us in still another team developing elementary science curriculum.
When it came to morning tea, we often had visitors and if we had a good crowd, Lynn would be unstoppable. She would introduce herself and then begin talking about her theory: she passionately believed that chloroplasts, the plant cell units which manufacture food for the plant and give plants their green color, were actually very primitive cyanobacterial cells (you might recognize them as blue-green algae) which had been gobbled up and then put to work making sugars as food for the gobbling cell.
There were a couple of papers early in the last century that vaguely suggested the idea. For Lynn it was an idea, a very big idea, that she had and considered very carefully and was trying it out at our coffee table. Every so often she also suggested that the powerhouse of almost all cells, certainly all of yours and mine, the mitochondria, were actually gobbled up intact and very much reduced bacterial cells.
We often had the very top scientific minds visit us who had the opportunity to hear Lynn expounding this theory. Other than vague suggestions, nothing like these ideas had ever been expressed so forcefully before and  Lynn was still a very young science professor. I heard more that one top scientific mind ask the question: ‘Who is this woman with this strange idea?’ We were listening in 1964 as she bounced her scientifically youthful ideas off these top scientific minds. Mostly, they were not amused, it seemed ridiculous to most of them.
At that time I was also a Harvard College (now Harvard University) Fellow. I spent quite a bit of time at Harvard and occasionally asked my colleagues what they thought about Lynn’s theory. The most common comment I heard was, ‘It will blow over.’ It was thought to be an interesting idea with no future.
Lynn submitted her first paper on her theories in 1966. As she told the story, it went to 15 scientific journals before it was accepted. It caused an enormous stir among biologists who read it- but today the theory is almost universally accepted and that paper, so disturbingly agitating to so many biologists, has become one of the cornerstone articles in 20th century biological history.
When two organisms live together in extremely close quarters, each benefiting from the other in some important way, we call the relationship symbiosis. In this case described by Lynn Margulis, when one kind of cell lives inside the other, the relationship could still be beneficial to both, In these cases, the result is called endosymbiosis, the ‘endo’ meaning ‘inside’. The host cell provides protection and perhaps some important chemicals. The gobbled cell uses carbon dioxide and water to make the nutrient, sugar, necessary for the life of the gobbling cell.  
It sounds like a great partnership, and it seems to have worked for millions of years. However, though the algal cells still contain at least some of their DNA in a single ring, typical of the simple cells of their group, they have become more and more reduced over time. Their job now is to manufacture and pump out sugars for the benefit of the gobbling plant cell.
However, each time the gobbling cell divides, the chloroplasts  divide and they divide just as cyanobacteria divide. Some chloroplasts go into one of the divided cells and the rest go into the other offspring cell. The division is almost never equal. There are almost always many chloroplasts in every gobbling cell or as we call them, in each plant cell. It does happen rarely that one of the divided cells gets no chloroplasts and then that cell will simply eventually starve to death. I can recall a corn plant germinating to grow into a pure white seedling. Pure white means that the egg cell from which the seedling grew, received no chloroplasts during the division of the mother cell. By chance, all the chloroplasts went into the other cell during division. When the storage food was exhausted the seedling died for lack of food. Food in plant cells is provided by chloroplasts.
As mentioned above the other subject of Lynn’s big idea was the mitochondrium. Mitochondria are often referred to as the ‘power houses’ of the cell.  Cell processes are powered when the chemical ‘ATP’ releases a lot of energy to become the chemical ‘ADP’. When I type this column, my mitochondria are producing ATP and when my fingers work to do the keyboarding, that work is powered when the ATP changes to ADP producing the energy needed. I just don’t know what I would do without my mitochondria making ATP. I couldn’t operate this keyboard and most certainly would be dead!
To Lynn, the answer to the question of mitochondria was solved. They were engulfed primitive bacteria which have become much reduced over the multi-millions of years they have lived inside the cells of all advanced organisms and almost all living cells which contain nuclei, That excludes the bacteria and the cyanobacteria which still form an important part of the living world.
When did the world of science finally accept Lynn’s idea that chloroplasts were reduced and enslaved cyanobacterial cells and mitochondria are reduced and enslaved bacterial cells? Electron microscopes provided the crucial evidence: every chloroplast and every mitochondrium contains a ring of DNA typical of all bacteria, whether cyano or just plain bacteria. That did it.
Though she continued to be feisty all her life, Lynn Margulis was eventually recognized with a number of medals and prizes. Perhaps the most prestigious of all was the Darwin Wallace Medal, given by the Linnaean Society of London every 50 years! In 2008 they gave out 13 of the coveted medals for contributions to the understanding of evolution, and to the dismay of her detractors, one went to went to Lynn. In this writer’s opinion, it was well deserved.