Experimental Discovery, Data Models, and Mechanisms in Biology: An Example from Mendel’s Work - Mechanism and Causality in Biology and Economics - page 100

mechanistic explanations. I also argue that experimental discovery usually precedes
and is a prerequisite for the discovery of mechanism. It plays a role in three ways:
organizing data into significant phenomena, producing the need and motivation to
discover mechanisms, and constraining the direction for construction of theoretical
hypotheses.

2 Problems with the Identification and Recognition
of Experimental Discoveries

In 1928, Frederick Griffith conducted a novel experiment on two strains of Pneu-
mococcus bacteria, known as the smooth (S) strain and the rough (R) strain for the
formation of colonies with smooth or rough surfaces, respectively. It was known
that the S-strain was virulent enough to kill mice and the R-strain avirulent. When
Griffith heated S-strain cells, killing them, and injected them into mice, the mice
lived. When he injected both heat-killed S-strain and live R-strain cells together
into mice, the mice frequently died. The process is summarized in Fig. 6.1 .
In examining the dead mice, Griffith found living S-strain cells in their bodies!
To Griffith, the experiment suggested that there must be something in the S-strain
heat-killed cells that could convert the R-strain avirulent cells to the lethal form.
What was this “something”? Why did it have such a capability? Griffith did not
find this something before he died in 1941. In a biology textbook, the authors
wrote, “This ability of some chemical substance in the dead bacteria to convert a
related strain to a genetically stable, new form was termed transformation. Later,
Avery, Macleod, and McCarty of the Rockefeller Institute determined that the
'transforming principle' was in fact DNA” (Villee et al. 1989 , p. 298).
Many historians recognize that Griffith did make a discovery, 1 but is it adequate
to call his findings from that experiment an experimental discovery? If so, what did
he discover? The novel phenomenon of transformation? Does he deserve recogni-
tion for that discovery? Does the recognition of his discovery rely on determination
of the transforming substance?
In 1892, Hans Driesch shook a sea urchin embryo at the two-cell stage so
vigorously that it became two separate cells. He observed that they developed
into complete embryos that were normal in configuration but smaller than natural
counterparts. He tried to separate cells from the embryo at the four- or eight-cell

1

A historian of molecular biology described this event: “[I]n 1928, Griffith in London had
published a startling discovery” (Judson 1996 , p. 18). Another historian of molecular biology
wrote: “In 1928, the British physician Fred Griffith discovered the strange phenomenon of
transformation” (Morange 1998 , p. 31). The evolutionist Ernst Mayr ( 1982 , p. 818) described
this event with similar locution: “In 1928 the British bacteriologist F. Griffith discovered that ”

The historian of general biology Lois Magner ( 2002 , p. 428) commented on Griffith's results: “In
retrospect, it can be said that Griffith has observed genetic transformation, but he probably did not
realize that the phenomenon he had discovered involved the transfer of hereditary material.”

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