To the editors:
In his essay, J. Scott Turner creatively brings together two of biology’s new frontiers: homeostasis and niche construction. Homeostasis involves the maintenance of an interior milieu that is partitioned off from the rest of the environment via adaptive boundaries and the maintenance of far-from-equilibrium stable states in relation to this interior environment. Niche construction, on the other hand, is the process by which organisms modify their own environments, doing so in ways that can be passed down to subsequent generations. Turner brings together these two conceptions in order to argue against the machine conception of life and to provide a basis for a more purpose-oriented picture of biological evolution. In my assessment, Turner’s arguments are sound, albeit with one caveat. Namely, the related inclusion of another new frontier in biology: autopoiesis.1
Autopoiesis is a concept that depicts life’s intrinsic logic—a biologic, if you will.2 It points to the intrinsically purposive processes by which mutually-embedded members belonging to the organism—organs, tissues, cells, and so on—operate together for the production and maintenance of the whole in the face of the counterforce that is entropy. What is living “organizes the production of its own components” purposively in order to maintain its integrity as a whole.3 Autopoietic processes can be seen in: the functioning of the immune system; cellular repair and replication; protein production; lipid synthesis, metabolism, and transportation; membrane formation; red and white blood cell production; blood clotting and wound healing; molecule and nutrient recognition; energy use; and the plethora of autonomously-regulated chemical reactions that occur inside the body. The organismic or cellular membrane itself, which marks its boundary and mediates between inner and outer as in physiological homeostasis, is produced and repaired by way of autopoietic processes. One way to interpret the meaning of autopoiesis is that it points to the basic hows underlying the maintenance of homeostatic far-from-equilibrium stable states internal to the physiological organism that allow it to persist as a whole in the face of entropy. Turner’s example concerning potassium management seems to involve intrinsically purposive autopoietic processes, although this term is not mentioned in the piece.
As described in Turner’s essay, termites purposively construct, repair, and rebuild the adaptive boundary that is their mound. The mound itself is not alive in the sense of being a bearer of autopoietic purposiveness. The maintenance of the mound’s structural integrity requires the ongoing activity of the termites, but the termites are neither reducible to mere parts of the mound, nor are they subordinate to any particular mound. The termites are alive, whereas the mound is not. Homeostasis, of itself, is not sufficient for a comprehensive definition of life. A reference to autopoietic processes is required alongside an outline of homeostatic workings. This argument may be seen to stand in the way of the speculative hypothesis described by Turner in The Extended Organism:
[A]nimal-built structures [can be] properly considered organs of physiology in principle no different from, and just as much a part of the organism as, the more conventionally defined organs such as kidneys, hearts, lungs, or livers.4
It is also seemingly antagonistic to the Gaia hypothesis that sees the earth as a single organism. In relation to the latter, there are homeostatic processes which do not require a reference to the intrinsic purposiveness of living organisms qua autopoiesis. However, I believe it represents a more accurate picture of our conditions of life on this planet: organisms are compositional parts of nature, but they are not to be equated with the sum total of nature.
Cognition, or mental autopoiesis, has emerged with reference to homeostasis. It involves processes of appropriation, self-production, and selection of conceptual structures that may enhance biological survival. Most importantly, mentality in some sense protrudes out from the physiological organism, and points to an awareness of the internal-external situation as well as (possibly) the anticipation of future conditions—a degree of what Daniel Dennett calls look-ahead.5 This provides organisms with an adaptive advantage in the struggle for existence.
Mentality is a condition for the possibility of the organism being able to direct action purposively for the sake of rectifying imbalances between what is internal to the organism and what is external. For example, a person feeling cold might build a fire or wrap themselves in animal skins—a behavioral regulation of body temperature. Mental awareness enables organisms to deal purposively with homeostatic imbalances that cannot be righted by the body’s automatic regulatory systems, or by pre-existing behavioral habits. Mentality enables downward causation to direct action purposively on the body or the environment and the purposive mediation between the internal and external, including the process of choosing between alternative responses or courses of action. As Turner suggests in Purpose and Desire, homeostasis “encompasses both internal and external environments,” involving the “coupling of information about the state of the environment on one side of an adaptive boundary to the matter and energy flows across” it.6 Such processes may involve mentality, yet they require a reference to the explanatory hows that are found in autopoiesis research.
All in all, Turner’s arguments are sound. My quibble is just that homeostasis requires a reference to autopoiesis, and vice-versa. It is by way of their interconnection that these concepts can provide a more holistic and comprehensive definition of life that is not subordinate to the prevailing machine conception of life and the strict anti-purposive leanings of mechanistic biology.
Adam Scarfe
J. Scott Turner replies:
I thank both Adrian Bejan and Adam Scarfe for their thoughtful comments on my essay. I agree with much in both of their responses. However, both raised questions in my mind that I think warrant exploring further.
The first concerns the question of how we—students of life—should think about life as a phenomenon. Biology has always been split on this question. On the one hand, biologists seek to emulate modes of inquiry appropriate to the physical sciences, the exemplar of this being molecular biology. This mindset is widespread throughout the various physiological sciences: the sciences concerned with how life works, in short. On the other hand, there are concerns with notions of form, mentality, history, and contingency, which include most prominently the human sciences, but more broadly the ecological and evolutionary sciences as well. These differing concerns would seem to call for different modes of inquiry from those that prevail in the physical sciences. Nevertheless, there has been for many years a strong tendency for students of life to emulate physicists and chemists, a tendency long ago described by Ernst Mayr as “physics envy.” Modern Darwinism is the triumphant exemplar of this.
Nevertheless, undercurrents of discontent run through our modern scientific discourse which can only be described as crypto-vitalist. What I have tried to do is to bring up a question that needs asking. Do we believe that life is a phenomenon unlike any other in the universe? If we answer “yes,” we are vitalists. It then becomes incumbent upon us to answer just what it is that makes life unique. My claim is that the answer to this question will not be found through physics envy.
Autopoiesis, as described by Adam Scarfe, is riven by a similar tension between frank and incipient truth. Autopoiesis expresses the organism in terms of self-organizing and self-forming of living systems. Indeed, that is the literal meaning of the term. The concept draws considerable inspiration from the Bernardian conception of homeostasis as a fundamental property of life, but autopoiesis adds to Bernard’s conception in significant ways. As Scarfe correctly points out, Bernard was concerned mostly with the internal environment (milieu interieur) of living systems. Autopoiesis expands upon this more broadly to include both the external and internal environments. Autopoiesis also brings in important ideas, such as the behavior of dissipative thermodynamics systems, that Bernard himself could never have conceived.
In this sense, the extended organism idea, which treats the organism as a homeostatic conspiracy of environments, owes a large debt to the autopoietic idea. However, autopoiesis sits with the same problem of agency as does the constructal theory. Autopoiesis sits very firmly in the machine metaphor for life, and so is quite at variance with Bernard’s own essentially vitalist conception of homeostasis. This shapes our discourse in some fundamental and often unacknowledged ways, which I have explored in more depth in Purpose and Desire. To put the matter briefly, what shapes what? The autopoietic idea treats homeostasis as mechanism, as an expression of the essentially mechanistic phenomenon of life’s distinctive property—autopoiesis. This turns Bernard’s conception on its head. Bernard’s vitalist logic has made autopoiesis (the mechanism) the outcome of homeostasis (the distinctive property). Looked at from one side, life is pure mechanism, the outcome of passive agency. Looked at from the other side, mind-filled and intention-driven agency rules.
Niche construction theory, mentioned by me as well as by Adam Scarfe, poses a similar difficulty. Is niche construction simply mechanism? In this case, niche construction theory is simply a special case of the machine metaphor for evolution that is modern Darwinism. Or is niche construction, the process, driven by mind and intentionality? I lean toward the latter, which in my mind makes niche construction theory the truly revolutionary idea it is.
It is an exciting time to be a biologist.
