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Physics of Life Reviews 9 (2012) 35–37 www.elsevier.com/locate/plrev
Comment
How uniquely irreducible is consciousness? Defining the limits of biological reductionism A commentary on Neuroontology, neurobiological naturalism, and consciousness: A challenge to scientific reduction and a solution, by Todd E. Feinberg, MD David B. Edelman a,b,∗ a The Neurosciences Institute, 10640 John Jay Hopkins Drive, San Diego, CA 92121, United States b The Scripps Research Institute, 10550 N Torrey Pines Rd, La Jolla, CA 92037, United States
Received 4 January 2012; accepted 5 January 2012 Available online 10 January 2012 Communicated by L. Perlovsky
Keywords: Consciousness; Biological irreducibility; Individual development; Organismal evolution; Animal form; Individual history
In this important and thought-provoking review, the author takes up what is certainly the central challenge to the scientific study of consciousness: namely, the apparent irreducibility of core aspects of subjective experience. The author rightly identifies four core features of consciousness that defy attempts at reduction: the referral of mental states, mental unity (taken here to be the same as ‘perceptual unity’), qualia, and mental causation [1, this issue]. For the sake of this commentary, I will consider an overarching claim made in the target review about the nature of reduction in biological systems generally. In framing the problem of irreducibility in the study of consciousness, the author begins with the observation that all biological systems are hierarchically organized. In such hierarchical systems, certain novel properties are emergent at the highest levels of organization (i.e., properties that differ markedly from the features that collectively generate them); at the same time, high-level components constrain the structural and functional properties of components hierarchically below them (e.g., ‘downward causation’) [1]. This is relatively uncontroversial, as, in principle, is the distinction the author draws between ‘strong’ emergent properties, which cannot be reduced to constituent components, and ‘weak’ emergent properties, which can at least be understood in terms of the principles and behavior of individual components [1]. But within the purview of modern biology, such a distinction is, I contend, not nearly as clear-cut as the author suggests. At the risk of mischaracterizing the author’s position, reinforced as it is by a few DOI of original article: 10.1016/j.plrev.2011.10.019. * Correspondence to: The Neurosciences Institute, 10640 John Jay Hopkins Drive, San Diego, CA 92121 United States. Tel.: +1 (858) 626 2000;
fax: +1 (858) 626 2099. E-mail address:
[email protected]. 1571-0645/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.plrev.2012.01.001
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examples of biological systems that seem to evince weak emergent features that can ultimately be reduced to more fundamental structural and functional properties, I believe that there remain profound reductionist challenges in at least two areas at the extremes of biology writ large: the processes of animal development (e.g., morphogenesis and embryogenesis) and organismal evolution. In regard to animal form and individual development, while we can say with reasonable certainty how particular genes encode specific proteins, how the function of those proteins is determined (at least in part) by the manner in which they are folded, how some proteins in turn regulate gene expression, enhancing or repressing the production of other protein products, and how protein expression and activity modulate cell structure and function, we cannot say with any degree of certainty how these myriad layers of interaction yield a functioning, three-dimensional organism (see [2–4]). Nor do we have the means to study developmental morphology in sufficient detail or at enough levels of interaction simultaneously to yield an answer to this question (though one might perhaps reasonably argue that this reflects merely the limits of present-day technology). More importantly, though, we can never hope to achieve a satisfactory mechanistic explanation for the origin of a given individual, even if we understand—down to the last detail—every constituent aspect of that individual’s biological makeup, including gene transcription, translation, and hierarchical regulation, protein chemistry and stoichiometry, intra- and extracellular signaling, cell adhesion, migration, differentiation, and death, organogenesis, epigenesis (which spatiotemporally subsumes much of the foregoing; see [2–6]), and any other level of structure or function that I have undoubtedly omitted. This is because we can neither observe nor reconstruct with perfect fidelity the staggeringly complex history of the individual, i.e., the cascade of events that profoundly and uniquely shaped—and continues to shape—that individual from conception to death. From the perspective of evolution, Darwinian or otherwise, while we might one day be able to achieve an understanding of the constituent properties that underlie the development of a ‘generic’ mammal (see [3–6]), we will never be able to say how a specific mammalian phenotype emerged in the first place. That particular evolutionary experiment—involving perhaps hundreds of thousands of interactions at many different levels—ran its course millions of years ago, and can never be repeated with 100% accuracy. Theodosius Dobzhansky was certainly right when he stated, “Nothing in biology makes sense except in the light of evolution. . .” [7]. But, here’s the point: it is only in hindsight that we can make sense of the emergence of complex animal forms. Unlike, say, a simple chemical reaction or the use of the polymerase chain reaction (PCR) to amplify a particular strand of DNA with near-100% fidelity, we cannot precisely reproduce the particular events that led to a specific taxon. Conscious experience is, I contend, similarly non-reducible in the sense that we can never reckon with the degree of complexity at the interface of organism and experience, i.e., the individual history that underlies much of the privileged nature of consciousness [8–10]. The foregoing is not so much intended to undermine the author’s premise that sensory consciousness can be conceived of as a weakly emergent system property, but rather to challenge the distinction drawn between weak and strong convergence in biological systems in the first place. The concept of ‘neurobiological naturalism,’ as formulated in the target review, is certainly compelling and in many ways is consistent with a view that I share: that, while consciousness is objectively and subjectively irreducible, its existence and scientific characterization do not require the rejection of existing physical properties in favor of new ones. Nevertheless, I believe that what is critically missing from this formulation is the role of individual history in the irreducibility of conscious experience. In this sense, the irreducibility of consciousness is not so fundamentally distinct from that of emergent properties arising from other biological systems, including individual development and organismal evolution. Acknowledgements The work of the author was supported by the Neurosciences Research Foundation. References [1] Feinberg TE. Neuroontology, neurobiological naturalism, and consciousness: a challenge to scientific reduction and a solution. Phys Life Rev 2012;9(1):13–34 [in this issue]. [2] Edelman GM. Topobiology: an introduction to molecular biology. New York: Basic Books; 1988. [3] Gould SJ. Ontogeny and phylogeny. Cambridge: The Belknap Press of Harvard University Press; 1985. [4] Raff RA, Kaufman TC. Embryos, genes, and evolution. New York: Macmillan Publishing Co., Inc.; 1983. [5] Løvtrup S. Epigenetics: a treatise on theoretical biology. London: John Wiley & Sons; 1974. [6] Nieuwkoop PD, Johnen AG, Albers B. The epigenetic nature of early chordate development: inductive interaction and competence. Cambridge, UK: Cambridge University Press; 1985.
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[7] [8] [9] [10]
Dobzhansky T. Biology, molecular and organismic. Amer Zool 1964;4:443–52. Edelman GM. The remembered present: a biological theory of consciousness. New York: Basic Books; 1990. Edelman GM. Wider than the sky: the phenomenal gift of consciousness. New Haven: Yale University Press; 2004. Edelman GM. Second nature: brain science and human nature. New Haven: Yale University Press; 2006.
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