Tracy Sonneborn

Tracy Morton Sonneborn ForMemRS (October 19, 1905 – January 26, 1981) was an American biologist. His life's study was of the protozoan group Paramecium.

Sonneborn attended the Baltimore City Public Schools and graduated from the Baltimore City College (high school) in 1922. As an adolescent, Sonneborn was interested in the humanities and considered becoming a rabbi. After taking a biology course taught by E. A. Andrews, his interest in literature was eclipsed by his interest in science. He earned a B.A. from Johns Hopkins University in 1925 and a Ph.D in 1928. His graduate work, supervised by Herbert S. Jennings, focused on the flatworm Stenostomum.

Sonneborn spent 1928 and 1929 researching the ciliate Colpidium with Jennings as a National Research Council fellow. He remained at Hopkins until 1939, with appointments as research assistant, research associate, and associate. He was offered a faculty position at Indiana University, where he served as associate professor, professor (1943), distinguished service professor (1953), and distinguished service professor emeritus (1976).

In the late 1950s he conducted an elegant series of experiments in his endeavours to discover what it is that mediates the synchronised movement of the paramecium's cilia. These minuscule hair-like projections enable the cell to 'swim'. They move together and paddle the cell through the water in which it lives.

The paramecium is a single-cell organism, so has nothing remotely resembling a brain. Yet its cilia move together like dancers in a ballet. How is it that their movements are co-ordinated?

Sonneborn surgically removed a small section of cell wall and replaced it rotated by 180 degrees. The cilia in the replaced section continued to 'wave' in the same direction as they had before surgery, i.e. now in antiphase to the others. What was remarkable is that both daughters of paramecia on which this operation had been performed also showed the same trait of a reverse phase wave in a similar area of their cell wall, as did, to a lesser extent, the granddaughter cells.

It is a mark of his excellence as a scientist that he should have taken the trouble to follow the fate of subsequent generations and so be able to make this observation. It may seem surprising that the clear evidence for non-Mendelian inheritance should have been largely overlooked by the scientific community. Further research was at that time limited because the available staining techniques to allow electron microscopy denatured the microtubules which 'power' the cilia so their presence in cells could not be seen. It may also be that, as at that time the mechanisms of genetic inheritance in DNA were becoming open to investigation, this example of non-Mendelian inheritance was not of great interest to the scientific community.

Sonneborn was an innovative teacher. He taught a course entitled Heredity, Evolution and Society that dealt with the science of genetics and the implications that technological advancements in that field held for society. One of his popular lectures involved students enacting the process of protein synthesis during which the genetic code is translated into the sequential addition of amino acids to form a polypeptide. His enthusiasm was infectious, and his lectures inspired students to study protozoa and algae.

Sonneborn married Ruth Meyers in 1929. Though educated as a social worker, she concentrated upon supporting her husband's career. They had two sons: Lee (1929–2004), a mathematician, and David (b. 1934), a biologist.