Correction needed in the School Education Group (McGraw Hill Glencoe) and Holt McDougal
Supplemental Biology Materials about the History of the Endosymbiotic Theory
by Steven Schafersman
The supplemental biology instructional materials submitted by the School Education Group, McGraw Hill Glencoe, have an error in the CINCH Lesson "The Origin of Life" used in the discussion of TEKS 7G and 9D about what they call the "endosymbiont theory." The discussion says:
In 1966, biologist Lynn Margulis proposed the endosymbiont theory. According to the endosymbiont theory, the ancestors of eukaryotic cells lived in association with prokaryotic cells.
When Margulis first proposed the endosymbiont theory, many scientists were hesitant to accept it.
The first and third sentences above are incorrect. The truth is that the endosymbiotic theory was first proposed by Russian Konstantin Mereschkowski in 1905 for plastids (chloroplasts). Next, Ivan Wallin extended the idea to include the endosymbiotic origin of mitochondria in the 1920s. These hypotheses were initially dismissed or ignored. The discovery that plastids and mitochondria contained their own DNA led to renewed interest in the hypothesis in the 1960s by several scientists. Then, in a 1967 paper, Lynn Margulis formally resuscitated the hypothesis and substantiated it with microbiological genetic evidence. She championed the hypothesis for several decades and it slowly gained acceptance; she deserves primary credit for this part. Today the endosymbiotic theory is taught in textbooks as accepted mainstream science, a notable result. Lynn Margulis deserves some credit for originating the theory but certainly not the sole credit. Konstantin Mereschkowski and Ivan Wallin deserve credit equal to Margulis. The McGraw Hill Glencoe supplement needs to be corrected.
Note added: 2011 July 22
It has come to my attention that Holt McDougal makes the same error in their chapter "7B Evolution of Life" on p. 456 of Chapter 19, History of Life on Earth, available on the website as file <7B Evolution of life.pdf>. The first sentence at the top of the page says this:
Mitochondria and chloroplasts likely originated as described by the endosymbiotic theory proposed by Lynn Margulis, which is illustrated in Figure 10.
Holt McDougal needs to correct this error.
Update: 2011 August 17
I have been informed by Holt McDougal that their editorial team has corrected this error.
Please see these references:
Ivan Emanuel Wallin (1883-1969)
At the time, most people believed mitochondria had evolved from the cell, but Wallin thought mitochondria might be bacteria, because they were indistinguishable by sight. He wrote a series of nine papers explaining his theories and experiments . . .
What Is Endosymbiosis?
Three biologists stand out in the history of the theory of endosymbiosis—the relationship in which a member of one species lives not just near or even permanently ON a member of another species, but INSIDE IT. The three biologists are Konstantin Merezhkovsky, Ivan Wallin, and Lynn Margulis.
"The crucial piece of evidence unavailable to Wallin until just before he died," writes Margulis, "was the discovery that mitochondria and plastids possess their very own DNA. Wallin knew though that mitochondria and plastids tend to reproduce at different times than do the cells in which they reside—as if demonstrating a residual impulse of their earlier, wilder days." Wallin, it turns out, correctly proposed that bacteria, the organisms which are popularly associated with disease, may represent the fundamental causative factor in the origin of species.
The Endosymbiotic Theory
The endosymbiotic (from the Greek: endo- meaning inside and -symbiosis meaning cohabiting) theory was first articulated by the Russian botanist Konstantin Mereschkowski in 1905. Mereschkowski was familiar with work by botanist Andreas Schimper, who had observed in 1883 that the division of chloroplasts in green plants closely resembled that of free-living cyanobacteria, and who had himself tentatively proposed (in a footnote) that green plants had arisen from a symbiotic union of two organisms. Ivan Wallin extended the idea of an endosymbiotic origin to mitochondria in the 1920s. These theories were initially dismissed or ignored. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example studies by Hans Ris), combined with the discovery that plastids and mitochondria contain their own DNA (which by that stage was recognized to be the hereditary material of organisms) led to a resurrection of the idea in the 1960s.
The endosymbiotic theory was advanced and substantiated with microbiological evidence by Lynn Margulis in a 1967 paper, The Origin of Mitosing Eukaryotic Cells. In her 1981 work Symbiosis in Cell Evolution she argued that eukaryotic cells originated as communities of interacting entities, including endosymbiotic spirochaetes that developed into eukaryotic flagella and cilia. This last idea has not received much acceptance, because flagella lack DNA and do not show ultrastructural similarities to bacteria or archaea.
Last updated: 2011 August 17