Experimental Discovery, Data Models, and Mechanisms in Biology: An Example from Mendel’s Work - Mechanism and Causality in Biology and Economics - page 101

S-strain R-strain heat-killed S live R+heat-killed S

injected
mouse dies

mouse lives mouse lives mouse dies

Fig. 6.1 Griffith's experimental procedure and results

embryo at two-cell stage embryo at four-cell stage

separated by shaking

c2

c1(cell) c1 c2 c3 c4

development

ce1(complete embryo) ce2 ce1 ce2 ce3 ce4

Fig. 6.2 Driesch's experimental procedure and results

stage and observed that all separated cells could develop normally. This result was
quite different from Driesch's expectation before the experiment, a surprising
phenomenon. Later, he explained it by adopting vitalism and the concept of vital
force. Driesch's experimental process is depicted in Fig. 6.2 .
This famous experiment conducted by Driesch at the end of the nineteenth
century provides an interesting contrast to Griffith's case. Some historians of
biology describe Driesch's experiment against the background of Wilhelm
Roux's hypothesis of mosaic development and frog-egg experiment, 2 treating
Driesch's work as a disproof or anomaly of Roux's “developmental mechanics.”
Instead of describing Driesch's experiment as a discovery, however, they label his
views as “extreme” or involving “confusion.” 3
Here we have a puzzle. Neither Driesch nor Griffith correctly interpreted his
experimental results. Why are historians pleased to declare that Griffith discovered
a new phenomenon but hesitant to attribute the same achievement to Driesch

2 Roux and Driesch are regarded as the cofounders of experimental embryology. But they held
opposite positions. Roux believed that the development of an embryo is determined by intrinsic
factors of eggs in a mechanistic way. He called this “self-differentiation” or “mosaic” develop-
ment, which means the capacity of the egg or of any part of the embryo to undergo further
differentiation independently of extraneous factors or of neighboring parts in the embryo. In other
words, parts of an embryo correspond to parts of a developed individual. Thus, Roux called the
new discipline employing his view and experimental approach “developmental mechanics.” To
confirm his beliefs, Roux conducted the famous “pricking experiment,” in which he destroyed one
of the cells of a frog embryo at the two-cell stage by pricking it with a hot needle. As a result, the
undamaged cell developed into a half embryo. See Magner ( 2002 , pp. 195-197).
3 Mayr ( 1982 , p. 118) wrote: “This unexpected amount of self-regulation induced Driesch, who
had performed this experiment, to embrace a rather extreme form of vitalism ”. Magner ( 2002 ,

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p. 198) commented: “ Driesch had apparently reached a more profound level of confusion,

which seemed to end all hope of finding a mechanistic explanation for development.” Neither did
other historians who mentioned Driesch describe his experiment in terms of “discovery” (Carlson
2004 ; Bowler 1989 ). Whatever their positions, all have expressed an ambiguous attitude toward
Driesch.

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