Saving Models from Phenomena: A Cautionary Tale from Membrane and Cell Biology
Axel Gelfert and Jacob Mok
Abstract This paper investigates one of the great achievements of twentieth- century cell biology: determining the structure of the cell membrane. This case differs in important ways from the better-known case of the identification of the DNA double helix as the carrier of genetic information, especially regarding the evaluation of potential evidence in light of prior theoretical commitments. Whereas it has been argued that adherence to a structural hypothesis enabled Watson and Crick to ignore a surplus of (potentially confusing) empirical findings, similar adherence to an elegant and universal structural hypothesis, we argue, unduly shielded the so-called ‘unit-membrane’ model from legitimate challenges on the basis of known phenomena.
Molecular cell biology has been the subject of a number of recent studies in the history and philosophy of biology.1 But the focus of attention has been uneven: whereas the search for the physical basis of heredity—culminating in the discovery of the DNA double helix and its genetic code—has been explored in much detail, other major developments in twentieth-century cell biology have yet to be analyzed in detail. This paper discusses one such example: the identification of the structure of the cell membrane. As we shall argue, this example not only casts light on how empirical findings gain the status of evidence, and how recognition of this status can be obstructed by prior theoretical commitments, but it also makes for an interesting contrast case to the discovery of the DNA double helix. In the latter case, considerable uncertainty about the physical basis of heredity was followed by an almost immediate consensus about the DNA double helix as the carrier of
1 Recent monographs include (Keller 2002), (Weber 2005), (Bechtel 2006), and many more.
A. Gelfert (*) • J. Mok
Department of Philosophy, National University of Singapore,
© Springer International Publishing AG 2017 17
F. Stadler (ed.), Integrated History and Philosophy of Science, Vienna Circle Institute Yearbook 20, DOI 10.1007/978-3-319-53258-5_2
genetic information; by contrast, in the membrane case, the majority view that membranes consisted of a lipid bilayer, uniformly coated with globular proteins— which held sway for more than 30 years—was only gradually challenged once new experimental techniques (such as freeze-fracture electron microscopy) were adopted in the 1960s and the evidentiary significance of previous findings and mismatches was recognized.
The rest of this paper is organized as follows: Section 2.2 reviews the interplay between models, theory, and evidence in the life sciences and introduces a useful recent distinction between signs and conditions of evidentiary success. Section 2.3 gives a detailed reconstruction of the development of membrane models in cell biology, paying special attention to ‘hits and misses’ in the evaluation of potential evidence. Section 2.4, in the light of this case study, argues for the inclusion of experimental techniques and epistemological strategies of their practitioners among the conditions of evidentiary success. Section 2.4 concludes the paper by contrasting the—guiding, yet also constraining—role of theoretical commitments in evaluating potential evidence for the complementary cases of membrane models and Watson and Crick’s DNA double helix model. Whereas in the latter case shielding the double helix model from prima facie disconfirming evidence turned out to have been a fortuitous shortcut to what we now take to be the best scientific account of the structure of DNA, the example of early membrane biology shows that trying to save a structurally appealing model from empirical challenges may lead to the tacit (and often unwarranted) dismissal of legitimate evidence, especially when such evidence is the result of new experimental techniques.