Thanks, Scott.

Yes, the more processual and dynamic concept of sympoiesis could be useful to our discussion. We believe that the generalization we are trying to make about symbiogenesis is also more dynamic than the one Margulis drew. In fact, we understand the formation of structures as a scale where dichotomies become blurred. Thus, in our article (see lines 182 to 226 of the preprint) we observe that it is the degree of irreversibility (mutual dependence) that allows us to move from individual to holobiont (sensu Margulis) to organism. We recognize, like you, that interactions can also be "external" (not necessarily endosymbiotic). Especially if Gaia is admitted, the difference between, for example, symbiotic bacteria that metabolize vitamin B within our body, and other Gaia “cell”  external to our body that synthesize vitamin C, which "we" then ingest, rather than absolute, is one of degree. 

We admit that the degree of symbiotic integration and irreversibility is very high in what traditional biology has identified as organism-individual and has classified since Linnaeus, but we extend it through ecological metabolisms (sensu your sympoiesis?) to the largest scale. In our article, we aim to lay out the main hypotheses and how their interactions give rise to an organic and evolving Gaia. We certainly use the framework of the laws of thermodynamics, as do other authors you also cite in your work. However, we take two further steps: 

First, as mentioned in Appendix A, the second law says nothing about whether or not there is a tendency to increase the rate or speed of entropy creation (the latter we assume and believe to be observable). Hence, we appeal to the TMaxPs as a reasonable hypothesis to apply precisely to systems such as those studied by biology or ecology. Nevertheless, we view thermodynamics and the TMaxPs as a facilitating rather than a directing force in the evolutionary processes of biology.

This is why, in a second step, we recur to Prigogine's trinomial (an analogous paradigm (Kauffmann, Maturana and Varela,...) would also be possible) that introduces two types of downward causation that we have called ‘organization/orchestration’ and ‘technique’. We believe this step to be important because it opens the door to biology as a discipline that cannot ultimately be reduced to (quantum) physics. The reason for this irreducibility lies in the properties that living beings in particular have, namely their capacity for expansion, which makes them collide with local limits or constraints, and which they are capable of breaking. This makes continuous evolution of life possible by the closure and the coupling of Prigogine trinomials through the process of generalized symbiogenesis (or sympoiesis?), which already belongs entirely to the biological-ecological realm and which we no longer observe in complex dissipative physical systems.

Thank you, Alejandro.

What constitutes life, an organism, a species, or an individual (e.g., as opposed to a holobiont)? These are questions that have been debated for centuries. In our view, which is reflected in the manuscript, nature neither is dichotomic nor behaves dichotomicallyy, and, thus, the terms and categories just mentioned might be perhaps better thought of in terms different shades of grey, rather than as black and white. 

That said, we acknowledge that Gaia represents a unique (super)organism and is therefore difficult to compare or reason about by analogies. Just as with FUCA (First Universal Common Ancestor), LECA (Last Eukaryotic Common Ancestor), or any primordial multicellular organism that emerged de novo—potentially with physical structures such as “the fur of a mink or the shell of a snail” (cf. Lovelock)—Gaia poses conceptual and definitional challenges.

Nonetheless, Gaia finds a useful analogy in the example you provided of the termite mound, which we also have used in our reference, taking as example the ‘organism’ Michaelensis. The Michaelensis organism is composed of the living “cells” of the termite mound—namely, the termites, fungi, and their bacterial symbionts—towards which its functions and objectives are directed. The physico-chemical structure that they construct and maintain, visible to us as the termite mound, would be analogous to Gaia’s Biosphere—the “house” Gaia has built for herself.

Of course, as with a termite mound, we again encounter definitional ambiguities concerning where the organism and the termite mound ends and how it modulates or influences its surrounding ecosystem. We would speak of Gaia’s interactions with systems external to the biosphere (e.g., plate tectonics, mantle dynamics) in a similar way, although the latter are clearly physical systems. They might have “self-organizing” qualities but we do not attribute to them inherent purposes or emergent goals in the way we do with living beings—whether understood through a “weak” teleology (as if) or a “strong” teleology (as is).

Thus, Earth System Sciences should not only study the influence of life/Gaia on the Earth System, but within the framework of the OGT ecology would be more appropriately understood as a form of physiology, and the biosphere as Gaia’s ‘termite mound’.

In any case, in the current article we have deliberately chosen not to delve too deeply into these conceptual aspects, given the manuscript’s already considerable length. Rather, we aim to elaborate a physical-biological theory that demonstrates the processes through which a singular individuality of extremely high organicity emerged—composed of “cells” with equally high internal organicity. These are processes that are, in fact, analogous to those that produced the first super-individuals during the major transitions in evolution (MTEs), such as LECA or the first termite mound—but occurring at a planetary scale.

In light of this, the next step in our research would be to assess Gaia’s degree of organicity and to determine whether this degree of organicity is indistinguishable, greater or smaller than the degree of organicity found in what we typically define as ‘organisms’.  Depending on the result, we might then classify Gaia accordingly. Otherwise, we risk falling into theoretical or possibly anthropocentric biases (e.g., we rarely view a beehive as a super-organism—perhaps simply because its “cells” are more spatially separated than what would be considered typical?).

In this sense, “we are cells of Gaia” is more than a metaphor—it is a scientific hypothesis, open to empirical testing. This is precisely because we now have a supporting scientific theory and because the physiological perspective that this theory implies, leads us to expect phenomena that differ from those predicted by cybernetic Gaia models, classical Earth System Science, or reductionist approaches in biology and ecology, which tend to focus on much smaller, less integrated organisms not organized at such a high, systemic level.