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Papers by Owen Gilbert

Rethinking Ecology, 2020

Throughout the history of life on earth, rare and complex innovations have periodically increased... more Throughout the history of life on earth, rare and complex innovations have periodically increased the efficiency with which abiotic free energy and biotic resources are converted to biomass and organismal diversity. Such macroevolutionary expansions have increased the total amount of abiotic free energy utilized by life and shaped the earth's ecosystems. Meanwhile, Darwin's theory of natural selection assumes a historical, worldwide state of effective resource limitation, which could not possibly be true if life evolved from one or a few original ancestors. In this paper, I analyze the self-contradiction in Darwin's theory that comes from viewing the world and universe as effectively resource limited. I then extend evolutionary theory to include a second deterministic evolutionary force, natural reward. Natural reward operates on complex inventions produced by natural selection and is analogous to the reward for innovation in human economic systems. I hypothesize that natural reward, when combined with climate change and extinction, leads to the increased innovativeness, or what I call the advancement, of life with time. I then discuss applications of the theory of natural reward to the evolution of evolvability, the apparent sudden appearance of new forms in the fossil record, and human economic evolution. I conclude that the theory of natural reward holds promise as an explanation for the historical advancement of life on earth.

Dictyostelium discoideum is normally a single-celled amoeba but, under starvation conditions, it ... more Dictyostelium discoideum is normally a single-celled amoeba but, under starvation conditions, it aggregates to form a fruiting body. About 80% of the cells become spores but the remaining 20% die to form a stalk to aid in the spores' dispersal. Thus, some cells sacrifice themselves to aid others, just as do social insect workers. Different clones can aggregate together and cheat each other by avoiding the stalk and making more spores (Strassmann et al. 2000). Knockout mutants can be made and we are studying a number of these mutants that cheat, with ...

Multicellular tissue compatibility, or histocompatibility, restricts fusion to close kin. Histo-c... more Multicellular tissue compatibility, or histocompatibility, restricts fusion to close kin. Histo-compatibility depends on hypervariable cue genes, which often have more than 100 alleles in a population. To explain the evolution of histocompatibility, I here take a historical ap-proach. I focus on the specific example of marine invertebrate histocompatibility. I use simple game theoretical models to show that histocompatibility can evolve through five steps. These steps include the evolution of indiscriminate fusion, the evolution of discrimi-natory within-organism conflict, the evolution of minor histocompatibility, the evolution of major histocompatibility, and the evolution of major histocompatibility cue polymorphism. Allowing for gradual evolution reveals discriminatory within-organism conflict as a selec-tive pressure for histocompatibility and associated cue polymorphism. Existing data from marine invertebrates and other organisms are consistent with this hypothesis.

Social amoebae aggregate to form a multicellular slug that migrates some distance. Most species p... more Social amoebae aggregate to form a multicellular slug that migrates some distance. Most species produce a stalk during migration, but some do not. We show that Dictyostelium giganteum, a species that produces stalk during migration, is able to traverse small gaps and utilize bacterial resources following gap traversal by shedding live cells. In contrast, we found that Dictyostelium discoideum, a species that does not produce stalk during migration, can traverse gaps only when in the presence of other species' stalks or other thin filaments. These findings suggest that production of stalk during migration allows traversal of gaps that commonly occurs in soil and leaf litter. Considering the functional consequences of a stalked migration may be important for explaining the evolutionary maintenance or loss of a stalked migration.

Recognition of relatives is important in microbes because they perform many behaviors that have c... more Recognition of relatives is important in microbes because they perform many behaviors that have costs to the actor while benefiting neighbors. Microbes cooperate for nourishment, movement, virulence, iron acquisition, protection, quorum sensing, and production of multicellular biofilms or fruiting bodies. Helping others is evolutionarily favored if it benefits others who share genes for helping, as specified by kin selection theory. If microbes generally find themselves in clonal patches, then no special means of discrimination is necessary. Much real discrimination is actually of kinds, not kin, as in poison-antidote systems, such as bacteriocins, in which cells benefit their own kind by poisoning others, and in adhesion systems, in which cells of the same kind bind together. These behaviors can elevate kinship generally and make cooperation easier to evolve and maintain. 349 Annu. Rev. Microbiol. 2011.65:349-367. Downloaded from www.annualreviews.org by 72.181.210.164 on 09/26/11. For personal use only.

Studies of genetic population structures of clonally reproducing macro-organisms have revealed la... more Studies of genetic population structures of clonally reproducing macro-organisms have revealed large areas where only one clone is found. These areas, referred to as clonal patches, have not been shown to occur in free-living microbes until now. In free-living microbes, high genetic diversity at local scales is usually maintained by high rates of dispersal. We report, however, a highly dense, 12-m clonal patch of the social amoeba Dictyostelium discoideum in a cattle pasture located in a Texas Gulf Coast prairie. We confirm the presence of only one clone by the analysis of 65 samples and amplification of 10 polymorphic microsatellite loci. Samplings of additional cattle pastures nearby showed higher clonal diversity, but with a density of D. discoideum isolates lower than in the clonal patch. These findings show that high rates of microbial dispersal do not always produce genetic diversity at local scales, contrary to the findings of previous studies. The existence of clonal patches may be particularly important for microbial social evolution.

The copepod Acartia tonsa is very sensitive to hydrodynamic signals, including those made by appr... more The copepod Acartia tonsa is very sensitive to hydrodynamic signals, including those made by approaching predators, and responds with a vigorous escape jump. Whether the presence of moderate turbulence changes this ability to detect hydrodynamic signals was investigated by comparing the response of copepods to velocity gradients created by a siphon flow in turbulent and still water. Turbulence decreased the distance at which A. tonsa initiated escapes from the siphon and increased the capture rate, indicating decreased sensitivity to hydrodynamic signals, but did not trigger unnecessary escape reactions that might produce fatigue.

Dissertation by Owen Gilbert

For decades, social amoebae have served as a model supporting broader theories of social behavior... more For decades, social amoebae have served as a model supporting broader theories of social behavior. Owing to their peculiar aggregative life cycle, it has seemed reasonable altruism in social amoebae is possible because of adaptive mechanisms of kin discrimination, and kin discrimination evolves to maintain this altruistic behavior. Nonetheless, these hypotheses have not withstood critical tests in social amoebae or other organisms. As a result, general theories of social evolution have rested on a few abstract theoretical assumptions.

Drafts by Owen Gilbert

arXiv.org, 2019

Darwin's first postulate was that the tendency of all organisms to increase in numbers will inevi... more Darwin's first postulate was that the tendency of all organisms to increase in numbers will inevitably outstrip resources [1], pp. 4, 63. With resource limitation, there is a competition between types for limited resources or what Darwin called the struggle for existence. Darwin reasoned that the most severe form of competition, leading to displacement of one type by another, would occur within species. Thus, Darwin identified the species as the evolving population. Dar-win also reasoned that because the types of organisms competing with each other belong to the same species, their variations would be slight, and modifications of form and function gradual. Darwin explained the origin of complex traits with models that conceptually break them into simpler components, and then chart their historical evolution [9-11]. By creating a historical theory for origins, which uses natural selection as a force acting for immediate benefits and through slight and successive modifications, Darwin advanced biology far beyond the teleological theories of Aristotle and Paley, which assumed that complex traits originate for their ultimate apparent functions [11-15]. Some of Darwin's contemporaries thus recognized that Darwin's theory "demolished" [16], or dealt a "death blow", to teleological thinking in biology [17]; [18], p. 330. How exactly did Darwinism challenge teleology? According to Darwin's logic, complex traits do not originate for the ultimate design purpose they appear to serve, as would be the case if they were intentionally designed by a Creator who planned every detail of existence [11-13, 15]. Instead, the course of evolution is determined by simple laws and the deterministic force of natural selection. Darwin [19], p. 51 noted that it was less derogatory to the Creator if He had formulated several simple laws, rather than each parasite and predator independently. More importantly for scientific questions, howev-Under Darwin's theory of evolution by natural selection, all beauty and wonder in nature comes from the diversity of life, ultimately created by a single evolutionary force. Darwin captured his sense of beauty with a powerful metaphor. Imagining himself sitting on the edge of a tangled bank, Darwin contemplated how a multitude of organic forms could have been derived from simple laws acting around him: growth with reproduction, inheritance, variability, and a struggle for existence leading to natural selection [1]. Within these laws, Darwin invoked natural selection as the only deterministic force (deterministic because it is both non-random and assumes the causes of events come before rather than after events). According to Darwin, natural selection causes slight modifications of form, function, and instinct that adapt a species to its immediate environment. Over time, evolution by natural selection leads to the origin of new complex structures and instincts, divergence of character, and the gradual change of species. On the historical backdrop of the dominant scientific debates of the time, the theory of natural selection created a dilemma. On the one hand, it suggested that all species had ultimately descended from one or a few forms. This suggested that major progressive patterns of evolution, as assumed by Lamarck [2] but contended by Lyell [3], were a real aspect of the history of life [4], pp. 337, 356. On the other hand, it did not explain long-term trends of increasing complexity or diversity. In recognition of this, Lyell wrote to Darwin and encouraged him to allow the possibility that natural selection was not the only guiding force and to "modestly limit the pretensions of selection" [5]. Darwin replied by arguing that natural selection was the only force and that Lyell invoked "miraculous additions" [6, 7]. To Darwin's objections, Lyell responded, "I care not for Creation, but I want something higher than Selection" [8]. Darwin's theory of evolution by natural selection does not predict long-term progress or advancement, nor does it provide a useful way to define or understand these concepts. Nevertheless, the history of life is marked by major trends that appear progressive, and seemingly more advanced forms of life have appeared. To reconcile theory and fact, evolutionists have proposed novel theories that extend natural selection to levels and time frames not justified by the original structure of Darwin's theory. To extend evolutionary theory without violating the most basic tenets of Darwinism, I here identify a separate struggle and an alternative evolutionary force. Owing to the abundant free energy in our universe, there is a struggle for supremacy that naturally rewards those that are first to invent novelties that allow exploitation of untapped resources. This natural reward comes in form of a temporary monopoly, which is granted to those who win a competitive race to innovate. By analogy to human economies, natural selection plays the role of nature's inventor, gradually fashioning inventions to the situation at hand, while natural reward plays the role of nature's entrepreneur, choosing which inventions to first disseminate to large markets. Natural reward leads to progress through a process of invention-conquest macroevolution, in which the dual forces of natural selection and natural reward create and disseminate major innovations. Over vast time frames, natural reward drives the advancement of life by a process of extinction-replacement megaevolution that releases constraints on progress and increases the innovativeness of life.

The dominant social-evolutionary paradigm implicitly equates social actions and behaviors causing... more The dominant social-evolutionary paradigm implicitly equates social actions and behaviors causing associations by extrapolating from models of social actions to explain behaviors affecting association. This extrapolation occurs when models of helping behavior are applied to explain aggregation or fusion, and when models of discriminatory helping behavior are applied to explain discriminatory segregation or discriminatory rejection. Here, I outline an alternative theoretical approach that explicitly distinguishes a social action as a helping or harming behavior, and an association as the context for a social action. Based on this distinction, I define a list of terms that allows a classification of association phenomena and the conceptual framework necessary to explain their evolution. I apply the resulting theory, which I call “association theory,” to identify a series of steps common to major and minor transitions in social evolution. These steps include the evolution of association, the evolution of differential treatment, the evolution of association preference, and the evolution of genetic kin recognition. I explain how to measure the parameters of association theory and I apply the theory to test Hamilton’s rule. I evaluate the evidence for association theory, including how it resolves anomalies of a former paradigm. Finally, I discuss association theory’s assumptions, and I explain why it may become the dominant framework for analyzing social evolution.

Rethinking Ecology, 2020

arXiv.org, 2019