Chemiosmotic coupling − the harnessing of electrochemical ion gradients across membranes to drive metabolism − is as universally conserved as the genetic code. As argued previously in these pages, such deep conservation suggests that ion gradients arose early in evolution, and might have played a role in the origin of life. Alkaline hydrothermal vents harbour pH gradients of similar polarity and magnitude to those employed by modern cells, one of many properties that make them attractive models for life's origin. Their (...) congruence with the physiology of anaerobic autotrophs that use the acetyl CoA pathway to fix CO2 gives the alkaline vent model broad appeal to biologists. Recently, however, a paper by Baz Jackson criticized the hypothesis, concluding that natural pH gradients were unlikely to have played any role in the origin of life. Unfortunately, Jackson mainly criticized his own interpretations of the theory, not what the literature says. This counterpoint is intended to set the record straight. (shrink)

Horizons of Difference offers twelve original essays inspired by Luce Irigaray's complex, nuanced critique of Western philosophy, culture, and metaphysics, and her call to rethink our relationship to ourselves and the world through sexuate difference. Contributors engage urgent topics in a range of fields, including trans feminist theory, feminist legal theory, film studies, critical race theory, social-political theory, philosophy of religion, environmental ethics, philosophical aesthetics, and critical pedagogy. In so doing, they aim to push the scope of Irigaray's work beyond (...) its horizon. Horizons of Difference seeks conversations that Irigaray herself has yet to fully consider and explores areas that stretch the limits of the notion of sexuate difference itself. Sexuate difference is a unifying mode of thought, bringing disparate disciplines and groups together. Yet it also resists unification in demanding that we continually rethink the basic coordinates of space, place, and identity. Ultimately, Horizons of Difference insists that the fragmented, wounded subjectivities within the dominant regime of masculine sameness can inform how we negotiate space, find place, and transform identity. (shrink)

We argued in Part 1 of this series that because all living systems are extremely far‐from‐equilibrium dynamic confections of matter, they must necessarily be driven to that state by the conversion of chemically specific external disequilibria into specific internal disequilibria. Such conversions require task‐specific macromolecular engines. We here argue that the same is not only true of life at its emergence; it is the enabling cause of that emergence; although here the external driving disequilibria, and the conversion engines needed must (...) have been abiotic. We argue further that the initial step in life's emergence can only create an extremely simple non‐equilibrium “seed” from which all the complexity of life must then develop. We assert that this complexity develops incrementally and progressively, each step tested for value added “in flight.” And we make the case that only the submarine alkaline hydrothermal vent (AHV) model has the potential to satisfy these requirements. (shrink)

The model of major transitions in evolution devised by Maynard Smith and Szathmáry has exerted tremendous influence over evolutionary theorists. Although MTE has been criticized for inconsistently combining different types of event, its ongoing appeal lies in depicting hierarchical increases in complexity by means of evolutionary transitions in individuality. In this paper, we consider the implications of major evolutionary events overlooked by MTE and its ETI-oriented successors, specifically the biological oxygenation of Earth, and the acquisitions of mitochondria and plastids. By (...) reflecting on these missed events, we reveal a central philosophical disagreement over the explanatory goals of major transitions theory that has yet to be made explicit in the literature. We go on to argue that this philosophical disagreement is only reinforced by Szathmáry’s recent revisions of MTE in the form of MTE 2.0. This finding motivates us to propose an alternative explanatory strategy: specifically, an interactionist metabolic perspective on major transitions. A metabolic framework not only avoids many of the criticisms that beset classic and revised MTE models, but also accommodates missing events and provides crucial explanatory components for standard major transitions. Although we do not provide a full-blown alternative theory and do not claim to achieve unity, we explain why foregrounding metabolism is crucial for any attempt to capture the major turning points in evolution, and why it does not lead to unmanageable pluralism. (shrink)

Here, I propose a new hypothesis: sex originated from an archaic gene transfer process among prebiotic bubbles without the prerequisite for reproduction. This de‐coupling from reproduction might make the thorny problem of accounting for the evolution of sex, despite the apparent advantages of parthenogenicity, more tractable.

Indoleamine 2,3‐dioxygenase (IDO) is the rate‐limiting enzyme in conversion of tryptophan to kynurenines, feeding de novo nicotinamide synthesis. IDO orchestrates materno‐foetal tolerance, increasing human reproductive fitness. IDO mediates immune suppression through depletion of tryptophan required by T lymphocytes and other mechanisms. IDO is expressed by alternatively activated macrophages, suspected to play a key role in tuberculosis (TB) pathogenesis. Unlike its human host, Mycobacterium tuberculosis can synthesize tryptophan, suggesting possible benefit to the host from infection with the microbe. Intriguingly, nicotinamide analogues (...) are used to treat TB. In reviewing this field, it is postulated that flux through the nicotinamide synthesis pathway reflects switching between aerobic glycolysis and oxidative phosphorylation in M. tuberculosis‐infected macrophages. The evolutionary cause of such shifts may be ancient mitochondrial behavior related to reproductive fitness. Evolutionary perspectives on the IDO pathway may elucidate why, after centuries of co‐existence with the Tubercle bacillus, humans still remain susceptible to TB disease. (shrink)

A replicator is simply something that makes copies of itself. There are hypothetical replicators (e.g., self-catalyzing chemical cycles) that are suspected to be unable to exhibit heritable variation. Variation in any of their constituent molecules would not lead them to produce offspring with those new variant molecules. Copying, such as in DNA replication or in xerox machines, allows any sequence to be remade and then sequence variations to be inherited. This distinction has been used against non-RNA-world hypotheses: without RNA replication (...) systems have no capacity to exhibit heritable variation. However, is copying the only way to have heritable variation? This article suggests that evolution can happen without anything being copied and that, in fact, RNA copying is too complex to arise spontaneously as the first pre-biotic system. There would then be a historical gradation of systems from non-alive to alive in which the capacity to have heritable changes would progressively increase and in which copying, as in template-based RNA-replication, would be a crucial but relatively late event. In addition, this article proposes a way by which RNA replication could have arisen, after systems able to evolve arose, as a crucial innovation and how that innovation spread over existing evolutionary systems and became a major driver of subsequent evolution. (shrink)

The details of abiogenesis, to date, remain a matter of debate and constitute a key mystery in science and philosophy. The prevailing scientific hypothesis implies an evolutionary process of increasing complexity on Earth starting from (self-) replicating polymers. Defining the cut-off point where life begins is another moot point beyond the scope of this article. We will instead walk through the known evolutionary steps that led from these first exceptional polymers to the vast network of living biomatter that spans our (...) world today, focusing in particular on perception, from simple biological feedback mechanisms to the complexity that allows for abstract thought. We will then project from the well-known to the unknown to gain a glimpse into what the universe aims to accomplish with living matter, just to find that if the universe had ever planned to be comprehended, evolution still has a long way to go. (shrink)

In the cytoplasm of practically all living cells, potassium is the major cation while sodium dominates in the media (seawater, extracellular fluids). Both prokaryotes and eukaryotes have elaborate mechanisms and spend significant energy to maintain this asymmetric K+/Na+ distribution. This essay proposes an original line of evidence to explain how bacteria selected potassium at the very beginning of the evolutionary process and why it remains essential for eukaryotes.

Origin of life models based on “energized assemblages of building blocks” are untenable in principle. This is fundamentally a consequence of the fact that any living system is in a physical state that is extremely far from equilibrium, a condition it must itself build and sustain. This in turn requires that it carries out all of its molecular transformations–obligatorily those that convert, and thereby create, disequilibria–using case‐specific mechanochemical macromolecular machines. Mass‐action solution chemistry is quite unable to do this. We argue (...) in Part 2 of this series that this inherent dependence of life on disequilibria‐converting macromolecular machines is also an obligatory requirement for life at its emergence. Therefore, life must have been launched by the operation of abiotic macromolecular machines driven by abiotic, but specifically “life‐like”, disequilibria, coopted from mineral precipitates that are chemically and physically active. Models grounded in “chemistry‐in‐a‐bag” ideas, however energized, should not be considered. (shrink)