Thursday, January 26, 2012

In Memory of Lynn Margulis

This essay will also be posted on my website at

One of the greatest evolutionary scientists, Lynn Margulis, died last November 22. In this essay I would like to reflect on her contributions to our understanding of the world. Not just of a narrow aspect of science, but the whole world.

Lynn was a child prodigy who began her university studies at age 14. In graduate school, she studied genetics, and married her fellow graduate student, Carl Sagan (who was as creative and large a thinker as she). She was not content to just learn what others said about genetics. She wanted to understand why some traits were inherited only through the mother’s side. These traits appeared to be passed on not through the chromosomes in the nucleus but through the mitochondria, which are tiny energy factories inside of most cells. Some plant traits appeared to be passed on through chloroplasts, the tiny green photosynthesis factories in many plant cells. This meant that mitochondria and chloroplasts had, and used, their own DNA. She wondered why they had that DNA. When she read about the work of some Russian scientists in the early twentieth century, she had her answer. Mitochondria and chloroplasts started off as bacteria, which moved into and took up residence inside of larger cells that already had nuclei. They did not consume the larger cell, nor did it consume them. Instead they formed a permanent partnership, which has been going on for billions of years. Mitochondria and chloroplasts began, she said, by symbiosis—cells living together. The result was the genesis of a new, complex kind of cell. She called this process symbiogenesis.

When Lynn Sagan (later Margulis) wrote her paper, it was rejected fifteen times. She was persistent. Finally it was published. At first her ideas were scorned. But in less than a decade, most biologists were convinced that she was right. When I went to hear her speak, while I was a sophomore at the University of California, Santa Barbara (it was the first scientific seminar I ever attended), she was well received, even though the professor who introduced her made some off-color jokes. At the time, I was a creationist, and I thought that there were only two alternatives to the origin of a complex cell: either gradual evolution, or sudden creation. Lynn Margulis presented a third alternative. Her view was entirely evolutionary, of course; but the host cell and the bacteria had evolved, separately and gradually, then suddenly merged together.

Today Margulis’s view of the origin of mitochondria and chloroplasts is a textbook standard. Scientists are working on an even more amazing example of symbiogenesis: many believe that the nucleus itself is the evolutionary descendant of a bacterium that moved into a larger cell that did not yet have a nucleus. I suspect that this idea would have been too wild even for Lynn in the early days.

In her final years, Lynn was looking for evidence that cilia and “flagella” of complex cells (such as paramecia) were the evolutionary descendants of spirochete bacteria. She had some good circumstantial evidence, but never did find proof.

She was also the principal biological champion of the “Gaia” view of the Earth, a view first proposed by atmospheric scientists James Lovelock. All of the organisms of the Earth form a single network of life. The Earth is therefore not just the home of life, but is alive. Not every component of the Earth is alive, of course; but neither is every component of a cell. A cell has living components, such as mitochondria, and nonliving components, such as water. But nobody would say that a cell is not alive. By the same reasoning, the Earth is alive.

Lynn was pugnacious. She was not afraid of a good scientific debate. And she was not afraid to be wrong. Clearly she was wrong in her assertion that HIV is not an infectious virus. But if she had never taken the risk of being wrong, would she ever have had the insights that changed modern biology?

I had a chance to talk with Lynn Margulis in 2004, as I was preparing my Encyclopedia of Evolution. She was 66 years old at the time, and could have retired comfortably and with renown. But she was still fighting for recognition of yet more of her insights. I mispronounced her name, and she corrected me: the emphasis is on the first syllable, Margulis. She said I would only be allowed to make that mistake once. I didn’t make it again. She enjoyed what I had written in my encyclopedia but was not afraid to point out what she considered errors. When I dedicated Life of Earth to her last year, she left me a phone message saying that the dedication brought tears of happiness to her eyes. She bought copies and left them for students to read at the University of Massachusetts, where she worked. I am glad to have brought a little joy and appreciation into the life of this great scientist.

We can carry on Lynn’s legacy if we continue to think big about the world. When Lynn started, most scientists were trying to decompose the big picture down into component parts. But now, many scientists consider that the interactions of those components are the most important thing. An entire research institute, the Santa Fe Institute, is devoted to understanding complex interactions and emergent properties. Geneticists now know that humans and mice have about the same number of genes, and most of them are the same genes; the big difference between a mouse and a human is not the genes but the interactions among the genes. I like to think that Lynn contributed greatly to this important change in the scientific view of the world.

Announcement: I just posted a new YouTube video on It will be up soon. Darwin comments on…Newt Gingrich?

Also, please send comments about what you would like to discuss, and thanks for the comments received.


  1. I just found out about Lynn Margulis' death from reading this blog. I can't decide what I find more distressing, news of her passing, or that I did not see it ANYWHERE! She was an unsung giant.

  2. I saw the announcement in a tiny space at the bottom of the page in Science.