The search for the hematopoietic stem cell: social interaction and epistemic success in immunology

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Abstract

Epistemology of science is currently polarized. Descriptive accounts of the social aspects of science coexist uneasily with normative accounts of scientific knowledge. This tension leads students of science to privilege one of these important aspects over the other. I use an episode of recent immunology research to develop an integrative account of scientific inquiry that resolves the tension between sociality and epistemic success. The search for the hematopoietic stem cell (HSC) by members of Irving Weissman’s laboratory at Stanford University Medical Center exhibits both the goal-oriented character of contemporary immunology and the importance of social interactions in successful achievement of those goals. This episode includes three kinds of epistemic success: characterization of HSC, formation of new interdisciplinary interfaces, and reconciliation of apparently incompatible models. All three depend on coordinating the work of diverse participants via social interactions. Together, they reveal the crucial role of social interactions within and between research groups in producing epistemic success. These features of the search for the HSC generalize to immunology as a whole, and plausibly to other disciplines. This account thus resolves the polarizing tension in epistemology of science, and complements individualistic accounts of scientific knowledge and rationality.

Introduction

It is a truism that science is social. Another truism is that science produces knowledge. However, these two apparently obvious claims co-exist uneasily. Their tension is one facet of a more general problem: the vexed relation between descriptive and normative aspects of science. Descriptive aspects of science are the focus of empirical case studies, historical or contemporary scientific episodes. Normative aspects comprise classic issues in philosophy of science: rationality, objectivity, progress and the growth of knowledge. Epistemologists have traditionally approached scientific knowledge in normative terms. On this approach, scientific knowledge is not equated with what is accepted as scientific knowledge at any particular time, but requires satisfaction of some standard of justification or truth-tracking, which defines epistemic success. The sociality of science, in contrast, is typically interpreted descriptively, in reference to various socio-cultural features of actual scientific inquiry. Taken together and so interpreted, the two truisms above capture a deep tension that polarizes current epistemology of science. Insofar as empirical studies of the social aspects of science are relevant to normative accounts, they seem to vitiate classic conceptions of epistemic success in science: progress, objectivity and rationality.1 Conversely, prominent normative accounts of scientific epistemology (e.g. Bayesianism, abduction) treat social aspects of science as irrelevant epiphenomena.2 It seems that students of science must privilege one aspect of science over the other. So there is a gap in recent epistemology of science, separating normative accounts of epistemic success from empirical studies of its social aspects.

Several prominent philosophers of science have recently offered accounts attempting to bridge this gap (Longino, 1990, Longino, 2002, Goldman, 1999, Kitcher, 2001, Solomon, 2001). However, none of these integrative attempts entirely succeeds. Longino’s (2002) account (critical constructive empiricism) goes furthest. She aims to reconcile traditional epistemology with recent sociology of science by rejecting the thesis that cognitive rationality and the influence of social factors on cognition are mutually exclusive alternatives. On Longino’s alternative, they are interdependent: empirical knowledge depends on constructive conceptual criticism from multiple perspectives incorporating different background assumptions, accomplished by interactions within and among communities of inquirers. Longino’s normative account has much to recommend it. However, she interprets sociality of science in terms of normative epistemology, vitiating engagement with descriptive sociological accounts.3 As a result, Longino’s normative account does not include a principled way of individuating knowledge producing communities in actual cases.4 But without such a method, Longino’s account cannot be applied to scientific episodes without engendering a regress of arguments over those very boundaries. Her ground-breaking social epistemic norms thus float free of actual science, leaving the original tension unresolved. Other recent accounts face similar difficulties. The normative force of Solomon’s social empiricism (2001) depends on controversial metaphysical claims. Although their respective accounts have many merits, Goldman (1999) and Kitcher (2001) sidestep the tension rather than resolving it, declaring many sociological aspects of science irrelevant. So, despite important recent efforts, the gap between normative accounts of scientific knowledge and empirical studies of the social aspects of science remains open.

This discontinuity weakens both approaches. Empirical sociological accounts that reject normative conceptions of scientific knowledge and epistemic success fit poorly with scientists’ own accounts of their work, and often seem to debunk or disparage it. Accounts of scientific rationality or objectivity that dismiss its social aspects look like fragmentary idealizations remote from actual practice, perhaps unattainable illusions we are better off without.

This debilitating tension can be resolved by filling in another gap in recent science studies: lack of attention to immunology. Immunology is a particularly appropriate field for examining both epistemic success and social interaction. First, it is a highly successful science. In little over a century, research in immunology has produced myriad facts, theories, models, methods and clinical applications, at an increasingly rapid rate.5 Practising immunologists refer to its growth as ‘startling’ or ‘explosive’ (Clark, 1991, Kuby, 1994, Paul, 2003). Historians and philosophers who attend to modern immunology also remark its rapid growth and advance (Söderqvist and Stillwell, 1999, Hacking, 2000, Darden, 2002). If epistemic success is at all correlated with these features, immunology should exhibit it. Social interactions are also prevalent in immunology research. The first sociological treatment of scientific knowledge, Ludwik Fleck’s Entstehung und Entwicklung einer wissenschaftlichen Tatsache (1935), focused on a widely applied immunological claim: ‘the Wassermann reaction is related to syphilis’ (Fleck, 1979, p. xxviii). More recent practitioners also emphasize the importance of social interactions in immunology research, noting that interdisciplinary collaboration, ‘debate, and the free exchange of ideas and technologies’ are crucial to its success (Stähelin, 1989, Doherty, 2002). Historians and philosophers of immunology emphasize its collaborative and critical aspects as well (Mazumdar, 1995, Keating and Cambrosio, 2003).6 Several scholars have suggested that success in immunology results from social interactions between scientists. Moulin (1989, p. 293) claims that increased theoretical coordination of the immunological community in the 1970s ‘contributed to the glorious expansion of immunology in that decade’. Löwy (2004, p. 391) argues that ‘the remarkable growth of immunology in the last thirty years is . . . a testimony to . . . the force of heterogeneous interactions’ between basic research and clinical medicine. However, these historical accounts do not engage with normative aspects of scientific epistemology. Here, I explicitly integrate social interaction and epistemic success in immunology.

This paper is organized as follows. Section 2 provides background: the basics of my approach (§2.1), an overview of current immunology (§2.2), and the development of the concept of the hematopoietic stem cell (HSC). Section 3 focuses on the Weissman group’s search for the HSC, beginning in the 1970s and continuing today. A fine-grained account of the search up to 1988 (§3.1) shows how different social interactions contribute to the complex, changing group structure of this line of inquiry. In Section 3.2, I distinguish three kinds of success in the Weissman group’s search, and show that each results from epistemically progressive social interactions. I then examine these social requirements for epistemic success in more detail (§4), and conclude with some remarks on their significance (§5).

Section snippets

Shared goals and social groups

We commonly understand and evaluate human actions in terms of the ‘fit’ between an agent’s goal and the means she takes to achieve it. By ‘action’ I mean intentional behavior performed by an agent, aimed at a goal. By ‘goal’ I mean ‘an object to which effort or ambition is directed’ (Oxford English dictionary, 2006). So, to have a goal is to be motivated to reach an objective that is specified in some way, however vaguely or imprecisely. We are accustomed to assessing the goals and actions of

The search (1967–1988)

In the late 1960s, Irving Weissman and his students at Stanford University Medical Center were investigating the immune function of the thymus.11 Their strategy was to remove blood cells from mouse thymus, characterize them by surface phenotype and then reintroduce ‘purified’ cells of a specific phenotype back into the thymus to determine their immune function (

Analysis

In summary: cast in terms of goal-oriented social action, the search for the HSC exhibits three kinds of success: (1) isolation and characterization of HSC; (2) formation of new interfaces with other sub-disciplines; (3) reconciliation of incompatible models of hematopoiesis. Each kind of success is recognized as such by participants and explicable in terms of goal achievement. In addition, all three have an epistemic aspect: more complete and consistent models of hematopoiesis obtained by

Conclusion

This account resolves the tension between sociality and epistemic success in scientific inquiry. Conceived as goal oriented social action, the search for the HSC integrates both aspects, with epistemic success emerging from progressive social interactions within and among research groups. All three kinds of epistemic success depend on coordinating the work of diverse participants via social interactions. Together, they reveal the epistemic significance of the complex social structure of

Acknowledgements

I thank Colin Allen, Arlene Bitmansour, Steve Crowley, Anthony DeTomaso, Karin Ekholm, Elihu Gerson, Tom Gieryn, Susan Oyama, Thomas Pradeu, Jutta Schickore and members of the Biology Studies Reading Group at Indiana University for valuable comments and criticism. An earlier version of this paper was presented at the 2005 meeting of the International Society for the History, Philosophy and Social Studies of Biology (Guelph, Ontario, 16 July 2005). Part of the argument was discussed at the 2006

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