Phototrophy, the conversion of light to biochemical energy, occurs throughout the Bacteria and plants, however, debate continues over how different phototrophic mechanisms and the bacteria that contain them are related. There are two types of phototrophic mechanisms in the Bacteria: reaction center type 1 (RC1) has core and core antenna domains that are parts of a single polypeptide, whereas reaction center type 2 (RC2) is composed of short core proteins without antenna domains. In cyanobacteria, RC2 is associated with separate core antenna proteins that are homologous to the core antenna domains of RC1. We reconstructed evolutionary relationships among phototrophic mechanisms based on a phylogeny of core antenna domains/proteins. Core antenna domains of 46 polypeptides were aligned, including the RC1 core proteins of heliobacteria, green sulfur bacteria, and photosystem I (PSI) of cyanobacteria and plastids, plus core antenna proteins of photosystem II (PSII) from cyanobacteria and plastids. Maximum likelihood, parsimony, and neighbor joining methods all supported a single phylogeny in which PSII core antenna proteins (PsbC, PsbB) arose within the cyanobacteria from duplications of the RC1-associated core antenna domains and accessory antenna proteins (IsiA, PcbA, PcbC) arose from duplications of PsbB. The data indicate an evolutionary history of RC1 in which an initially homodimeric reaction center was vertically transmitted to green sulfur bacteria, heliobacteria, and an ancestor of cyanobacteria. A heterodimeric RC1 (=PSI) then arose within the cyanobacterial lineage. In this scenario, the current diversity of core antenna domains/proteins is explained without a need to invoke horizontal transfer.
Over the past 10 years, it has become unpopular to talk about definitions of life, under the assumption that attempts at a precise definition are counterproductive. Recent attempts have failed to meet strict philosophical criteria for definitions and have failed to reach consensus. I argue that provisional definitions are necessary for clear communications. Our current knowledge of biology justifies a number of universal claims about the category of life. Whether or not "life" represents a natural category, it maps to a number of important, observable processes. Given the importance of those processes and the extent of our knowledge, plural explicit definitions of life (and related categories) will be necessary for progress in astrobiology and origin-of-life studies as well as biology in general. I propose concrete categories related to, but not necessarily coextensive with, life for clear communication and hypothesis formation: Woese life, Darwin life, Haldane life.
Pale Blue Dot" and "Anthropocene" are common tropes in astrobiology and often appear in ethical arguments. Both support a decentering of human life relative to biological life in terms of value. This article introduces a typology of life-value narratives: hierarchical narratives with human life above other life and holistic narratives with human life among other life. Astrobiology, through the two tropes, supports holistic narratives, but this should not be viewed as opposed to Christianity. Rather, Christian scriptures provide seeds of both hierarchical and holistic narratives, each of which may flourish in different environments. By attending to which aspects of human life are valued-or disvalued-relative to biological life, we can better understand how life-concepts do work in ethics, anthropology, and soteriology in secular as well as theological contexts.Astrobiology does not decenter humanity. Popular press about astrobiology suggests that we, for the first time in human history, can apply science to age-old questions of meaning and purpose, but this distorts both the theological and scientific realities. Theologically, Christianity has been in dialogue with observations of the world for millennia and draws on multiple life-value narratives found in scriptures. Scientifically, the very concept of "centering" requires evaluative claims alien to objective research. Astrobiology does provide greater perspective into the way humanity relates Lucas John Mix is a member
Creating a unified model of life in the universe – history, extent and future – requires both scientific and humanities research. One way that humanities can contribute is by investigating the relationship between philosophical commitments and data. Making those commitments transparent allows scientists to use the data more fully. Insights in four areas – history, ethics, religion and probability – demonstrate the value of careful, astrobiology-specific humanities research for improving how we talk and think about astrobiology as a whole. First, astrobiology has a long and influential history. Second, astrobiology does not decentre humanity, either physically or ethically. Third, astrobiology is broadly compatible with major world religions. Finally, claims about the probability of life arising or existing elsewhere rest heavily on philosophical priors. In all four cases, identifying philosophical commitments clarifies the ways in which data can tell us about life.
The Astrobiology Primer has been created as a reference tool for those who are interested in the interdisciplinary field of astrobiology. The field incorporates many diverse research endeavors, but it is our hope that this slim volume will present the reader with all he or she needs to know to become involved and to understand, at least at a fundamental level, the state of the art. Each section includes a brief overview of a topic and a short list of readable and important literature for those interested in deeper knowledge. Because of the great diversity of material, each section was written by a different author with a different expertise. Contributors, authors, and editors are listed at the beginning, along with a list of those chapters and sections for which they were responsible. We are deeply indebted to the NASA Astrobiology Institute (NAI), in particular to Estelle Dodson, David Morrison, Ed Goolish, Krisstina Wilmoth, and Rose Grymes for their continued enthusiasm and support. The Primer came about in large part because of NAI support for graduate student research, collaboration, and inclusion as well as direct funding. We have entitled the Primer version 1 in hope that it will be only the first in a series, whose future volumes will be produced every 3-5 years. This way we can insure that the Primer keeps up with the current state of research. We hope that it will be a great resource for anyone trying to stay abreast of an ever-changing field.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.