8/28/2023 0 Comments Fragment synonym biology![]() ![]() In the case of life, scientists are interested in the nature of life they are not interested in what the word "life" happens to mean in our language. Such efforts reflect fundamental misunderstandings about the nature and power of definitions.ĭefinitions tell us about the meanings of words in our language, as opposed to telling us about the nature of the world. In a recent paper in Origins of Life and Evolution of the Biosphere, Christopher Chyba and I argue that it is a mistake to try to define 'life'. Q: What is your opinion of attempts to define of "life?" "I am interested in formulating a strategy for searching for extraterrestrial life that allows one to push the boundaries of our Earth-centric concepts of life." -Carol Cleland Sabbatical in Madrid, Spain, at the Centro de Astrobiologia (CSIC-INTA), she shared her thoughts on the power of definitions to shape science and philosophy. Carol Cleland, who teaches philosophy at Colorado University in Boulder and is a member of NASA's Astrobiology Institute. The recent addition of extremophiles (archaea) to the tree of life underscores the notion that life is defined by what we know, what we have seen before, and often what we have succeeded in domesticating to a laboratory petri dish.Īstrobiology Magazine sought out expert opinion on this important question from Dr. These classifications clarify the grand puzzle of existing life, but do little to provide a final definition.ĭefining life takes on a more bewitching character when extended beyond the Earth's biosphere. The final grouping includes the viruses, which don't have cells at all, but fragments of DNA and RNA that parasitically reproduce when they infect a compatible host cell. ![]() The eukaryotes include all organisms whose cells have a nucleus - so humans and all other animals are eukaryotes, as are plants, protists, and fungi. Bacteria, often referred to as prokaryotes, generally lack chlorophyll (except for cyanobacteria) and a cell nucleus, and they ferment and respire to produce energy. Archaea are the recently defined branch that often survives in extreme environments as single cells, and they share traits with both bacteria and eukaryotes. Terrestrially, life is classified among four biological families: archaea, bacteria, eukaryotes, and viruses. If these tendencies make for a rich set of characteristics, they have been criticized as ignoring the history of life itself. In hopes of restricting the working definition at least terrestrially, all known organisms seem to share a carbon-based chemistry, depend on water, and leave behind fossils with carbon or sulfur isotopes that point to present or past metabolism. While a "bright line" definition is needed, the borderline cases give life's definition a distinctly gray and fuzzy quality. For example, a crystal can grow, reach equilibrium, and even move in response to stimuli, but lacks what commonly would be thought of as a biological nervous system. To qualify as a living thing, a creature must meet some variation for all these criteria. To grow and develop, living creatures need foremost to be consumers, since growth includes changing biomass, creating new individuals, and the shedding of waste. Life is reproductive, as some kind of copying is needed for evolution to take hold through a population's mutation and natural selection. Living creatures respond, and their stimulation fosters a reaction-like motion, recoil, and inĪdvanced forms, learning. Organisms tend toward homeostasis: an equilibrium of parameters that define their internal environment. They have the ability to take in energy from the environment and transform it for growth and reproduction. Living things tend to be complex and highly organized. ![]() However, some initial agreement is possible. ![]() How to define " life" is a sweeping question that affects whole branches of biology, biochemistry, genetics, and ultimately the search for life elsewhere in the universe.Ĭomparing the semantic task to the ancient Hindu story of identifying an elephant by having each of six blind men touch only the tail, the trunk, or the leg, what answer a biologist might give can differ dramatically from the answer given by a theoretical physicist. Image Credit: National Ignition Facility Programs A crystal can grow, reach equilibrium, and even move in response to stimuli, but lacks what commonly would be thought of as a biological nervous system. ![]()
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