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The chin, a distinguishing feature of Homo sapiens, has sparked ongoing debates regarding its evolutionary origins and adaptive significance. We contend that these controversies stem from a fundamental disagreement about what constitutes a well-defined biological trait, a problem that has received insufficient attention despite its recognized importance in biology. In this paper, we leverage paleoanthropological research on the human chin to investigate the general issue of character or trait identification. First, we examine four accounts of the human chin from the existing literature: the mandibular differential growth byproduct, the bony prominence, the inverted T-relief, and the symphyseal angle. We then generalize from these accounts and propose a three-stage framework for the process of character identification: description, detection, and justification. We use this framework to reinterpret the four accounts, elucidating key points of contention surrounding the chin as well as other morphological characters. We show that debates over the chin carry broad and important biological implications that extend beyond this trait and that are not mere semantic issues of definition.

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Organismal death is foundational to the evolution of life, and many biological concepts such as natural selection and life history strategy are so fashioned only because individuals are mortal. Organisms, irrespective of their organization, are composed of basic functional units-cells-and it is our understanding of cell death that lies at the heart of most general explanatory frameworks for organismal mortality. Cell death can be exogenous, arising from transmissible diseases, predation, or other misfortunes, but there are also endogenous forms of death that are sometimes the result of adaptive evolution. These endogenous forms of death-often labeled programmed cell death, PCD-originated in the earliest cells and are maintained across the tree of life. Here, we consider two problematic issues related to PCD (and cell mortality generally). First, we trace the original discoveries of cell death from the nineteenth century and place current conceptions of PCD in their historical context. Revisions of our understanding of PCD demand a reassessment of its origin. Our second aim is thus to structure the proposed origin explanations of PCD into coherent arguments. In our analysis we argue for the evolutionary concept of PCD and the viral defense-immunity hypothesis for the origin of PCD. We suggest that this framework offers a plausible account of PCD early in the history of life, and also provides an epistemic basis for the future development of a general evolutionary account of mortality.

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Theoretical frameworks concerning cell fate typically center on proximate causes to explain how cells know what type they are meant to become. While major advances in cell fate theory have been achieved by these mechanism-focused frameworks, there are some aspects of cell decision-making that require an evolutionary interpretation. While mechanistic biologists sometimes turn to evolutionary theory to gain insights about cell fate (cancer is a good example), it is not entirely clear in cell fate theory what insights evolutionary theory can add, and why in some cases it is required for understanding cell fate. In this perspective we draw on our work on cellular mortality to illustrate how evolutionary theory provides an explanation for death being selected as one of the potential cell fates. Using our hypothesis for why some microbes in a community choose death as their fate, we suggest that some insights in cell fate theory are inaccessible to a theoretical framework that focuses solely on proximate causes.

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Programmed cell death (PCD) in unicellular organisms is in some instances an altruistic trait. When the beneficiaries are clones or close kin, kin selection theory may be used to explain the evolution of the trait, and when the trait evolves in groups of distantly related individuals, group or multilevel selection theory is invoked. In mixed microbial communities, the benefits are also available to unrelated taxa. But the evolutionary ecology of PCD in communities is poorly understood. Few hypotheses have been offered concerning the community role of PCD despite its far-reaching effects. The hypothesis we consider here is that PCD is a black queen. The Black Queen Hypothesis (BQH) outlines how public goods arising from a leaky function are exploited by other taxa in the community. Black Queen (BQ) traits are essential for community survival, but only some members bear the cost of possessing them, while others lose the trait In addition, BQ traits have been defined in terms of adaptive gene loss, and it is unknown whether this has occurred for PCD. Our conclusion is that PCD fulfils the two most important criteria of a BQ (leakiness and costliness), but that more empirical data are needed for assessing the remaining two criteria. In addition, we hold that for viewing PCD as a BQ, the original BQH needs to include social traits. Thus, despite some empirical and conceptual shortcomings, the BQH provides a helpful avenue for investigating PCD in microbial communities.

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We introduce here evoText, a new tool for automated analysis of the literature in the biological sciences. evoText contains a database of hundreds of thousands of journal articles and an array of analysis tools for generating quantitative data on the nature and history of life science, especially ecology and evolutionary biology. This article describes the features of evoText, presents a variety of examples of the kinds of analyses that evoText can run, and offers a brief tutorial describing how to use it.

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There is clearly a plurality of forms of altruism. Classically, biological altruism is distinguished from psychological altruism. Recent discussions of altruism have attempted to distinguish even more forms of altruism. I will focus on three altruism concepts, biological altruism, psychological altruism, and helping altruism. The questions I am concerned with here are, first, how should we understand these concepts? and second, what relationship do these concepts bear to one another? In particular, is there an essence to altruism that unifies these concepts? I suggest that while there is no essence to altruism, this does not mean that the array of altruism concepts is completely disunified. Instead, I propose we place all the concepts into a common framework-an altruism space-that could lead to new questions about how this space can be filled.

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Innovation is a key component of most definitions of culture and intelligence. Additionally, innovations may affect a species' ecology and evolution. Nonetheless, conceptual and empirical work on innovation has only recently begun. In particular, largely because the existing operational definition (first occurrence in a population) requires long-term studies of populations, there has been no systematic study of innovation in wild animals. To facilitate such study, we have produced a new definition of innovation: Innovation is the process that generates in an individual a novel learned behavior that is not simply a consequence of social learning or environmental induction. Using this definition, we propose a new operational approach for distinguishing innovations in the field. The operational criteria employ information from the following sources: (1) the behavior's geographic and local prevalence and individual frequency; (2) properties of the behavior, such as the social role of the behavior, the context in which the behavior is exhibited, and its similarity to other behaviors; (3) changes in the occurrence of the behavior over time; and (4) knowledge of spontaneous or experimentally induced behavior in captivity. These criteria do not require long-term studies at a single site, but information from multiple populations of a species will generally be needed. These criteria are systematized into a dichotomous key that can be used to assess whether a behavior observed in the field is likely to be an innovation.

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There are three related criteria that a concept of fitness should be able to meet: it should render the principle of natural selection non-tautologous and it should be explanatory and predictive. I argue that for fitness to be able to fulfill these criteria, it cannot be a property that changes over the course of an individual's life. Rather, I introduce a fitness concept--Block Fitness--and argue that an individual's genes and environment fix its fitness in such a way that each individual's fitness has a fixed value over its lifetime.

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