Margarida Hermida

The original Gaia hypothesis purports to explain the long-term maintenance of the Earth’s habitability by proposing that the biosphere has evolved homeostatic control of environmental parameters crucial to its survival. This idea was criticized for being incompatible with core Darwinian requirements for evolution by natural selection, since the biosphere is not part of a population of entities with variation, reproduction and heredity. Recently, however, some authors have defended a ‘Darwinized’ version of the Gaia hypothesis. Proponents of Darwinized Gaia argue that there can be natural selection for persistence alone, with no need for reproduction or competition, and that a single lineage can undergo a process of sequential selection over time. This article examines these ideas in the light of two important distinctions in evolutionary biology: adaptation versus by-product, and transformational versus variational explanation. Despite these new interesting ideas, however, the Darwinized Gaia hypothesis still cannot overcome the main objections from evolutionary biology.

The consensus in philosophy of biology seems to be that although nothing in biological systems is strictly incompatible with physical laws, biology is to a very great extent autonomous from physics. The main thesis of this paper is that, although biology is autonomous from the physical sciences in several ways, it is not explanatorily independent from physics. Physical explanations are pervasive and important in biology, including in evolutionary biology. The paper presents three case studies of physical explanations in evolutionary biology: a case of adaptation to pressure in deep-sea invertebrates, which illustrates how a physical parameter imposes selective pressures that organisms adapt to by changing their own physical properties; the case of water viscosity and the evolution of multicellularity, which shows how a global change in a physical parameter is thought to have triggered a macroevolutionary event; and the case of quantum tunnelling in respiration, which shows how quantum physics is relevant to the evolution of sex in eukaryotes.

It is often claimed that biology is autonomous from the physical sciences, but this is seldom made precise. This article makes explicit, for the first time, five distinct “autonomy of biology” theses. Three moderate theses concerning scientific status, methodological distinctness, and nonreducibility of biology to physics are correct and are nearly universally accepted. Two stronger theses, concerning the exclusivity of biological explanation and irrelevance of physical laws, are shown to be false on the basis of two case studies of physical explanations of biological phenomena. Which scales and laws are explanatorily relevant for a particular phenomenon must be decided empirically.

An essentialist claim often made about organisms is that they could not have originated in different gametes. The thesis of gametic essentialism (GE) is usually understood either as a particular case of material origin essentialism, or as genetic essentialism. This paper argues that it should instead be understood in terms of the numerical identity of the gametes. Since gametes are living cells, their identity conditions should be the same as those of other living beings, and therefore involve neither specific material composition, nor specific genes, but continuity of the same life. Understood in this way, GE is a particular case of biological antecedents essentialism (BAE), a kind of origin essentialism that is better justified in the light of the metaphysical nature of organisms as objects that inherit life from previously existing living organisms. BAE overcomes many objections facing other origin essentialist accounts, and it recognises the importance of the gametes in transmitting not just genes, but actively functioning physical structures necessary for life. If we wish to maintain an origin essentialism principle for organisms, we should prefer BAE.

Animalism is prima facie the most plausible view about what we are; it aligns better with science and common sense, and is metaphysically more parsimonious. Thought experiments involving the brain, however, tend to elicit intuitions contrary to animalism. In this paper, I examine two classical thought experiments from the literature, brain transplant and cerebrum transplant, and a new one, cerebrum regeneration. I argue that they are theoretically possible, but that a scientifically informed account of what would actually happen shows that in none of the cases would the person be separated from the animal. Our intuitions in these cases, when adequately informed by neuroscience, do not conflict with animalism – rather, they suggest a correction of the animalist position: the persisting animal should be at least minimally sentient. Sentience animalism is a new formulation of the animalist account of personal identity that allows us to reconcile facts about our biological persistence conditions with the intuition that human persistence should involve some kind of psychological continuity.

In The Expanse, the future of humanity is constantly at stake. In The Expanse vestiges of an ancient alien civilization with incredibly advanced technology have been found—which eventually permits human interstellar expansion through the gates. James Lenman argues that, even if we agree that biodiversity is a good thing, it only means that it's good that there should be natural diversity while life exists on Earth. While we might not be facing interplanetary war or the unpredictable consequences of ancient alien technology, many serious dangers face the human species today. We are quite resilient and have survived numerous disasters in the past, including floods, earthquakes, famine, pandemics, and wars. Small population size and restricted distribution range are factors that increase a species’ extinction risk. Interplanetary expansion could potentially bring about speciation, which means the separation of Homo sapiens into different species.

This paper addresses the question ‘what is an organism?’. Extant theories of organismality only provide a partial answer because they do not include an account of composition on which an ontology of living entities can be based. Here we develop a new account of what organisms are, based on a naturalistic answer to the special composition question, the bound state view. We argue that physical structure, including the existence of a boundary, is essential for life, and that, therefore, organisms are a particular kind of composite physical object – living objects. The bound state account of composition explains how composite physical objects exist in the world, and the property ‘life’ distinguishes the subset of those objects which are organisms. Our view obviates the need for disjunctive accounts of composition for living and non-living entities, placing ‘organism’ within the context of a broader scientific ontology, while at the same time providing a clear criterion of organismality that can be used in adjudicating problematic cases of biological individuality.

Some plausibly necessary a posteriori theoretical claims include ‘water is H 2 O’, ‘gold is the element with atomic number 79’, and ‘cats are animals’. In this paper I challenge the necessity of the third claim. I argue that there are possible worlds in which cats exist, but are not animals. Under any of the species concepts currently accepted in biology, organisms do not belong essentially to their species. This is equally true of their ancestors. In phylogenetic systematics, monophyletic clades such as the animal kingdom are composed of an ancestral stem species and all of its descendants. If the stem species had not existed, neither would the clade. Thus it could have been the case that all the organisms which actually belong to the animal kingdom might have existed yet not have been animals.

Life on Earth descends from a common ancestor. However, it is likely that there are other instances of life in the universe. If so, each abiogenesis event will have given rise to an independently originated life clade, of which Earth-life is an example. In this paper, I argue that the set of all IOLCs in the universe forms a Darwinian population subject to natural selection, with more widely dispersed IOLCs being less likely to face extinction. As a result, we should expect that, over time, more planets will become inhabited by fewer, more successful IOLCs.

Life is a self-maintaining process based on metabolism. Something is said to be alive when it exhibits organization and is actively involved in its own continued existence through carrying out metabolic processes. A life is a spatio-temporally restricted event, which continues while the life processes are occurring in a particular chunk of matter (or, arguably, when they are temporally suspended, but can be restarted at any moment), even though there is continuous replacement of parts. Life is organized in discrete packages, particular cells and multicellular organisms with differing degrees of individuality. Biological species, too, have been shown to be individuals, and not classes, as these collections of organisms are spatio-temporally localized, restricted, continuous, and somewhat cohesive entities, with a definite beginning and end. Assuming that all life on Earth has a common origin, all living organisms, cells, and tissues descending from this origin exhibit continuity of the life processes at the cellular level, as well as many of the features that define the individual character of species: spatio-temporal localization and restriction, continuity, historicity, and cohesiveness. Therefore, life on Earth is an ontological individual. Independent origins of life will have produced other such individuals. These provisionally called ‘life-individuals’ constitute a category of organization of life which has seldom been recognized. The discovery of at least one independent life-individual would go a long way toward the project of the universality of biology.