Ranjeet Patil - биография, образование и работа

lokiSome of the earliest theories of life were materialist, holding that all that exists is matter, and that all life is merely a complex form or arrangement of matter. Empedocles (430 B.C.) argued that every thing in the universe is made up of a combination of four eternal 'elements' or 'roots of all': earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. For example, growth in plants is explained by the natural downward movement of earth and the natural upward movement of fire.[7] Democritus (460 B.C.), the disciple of Leucippus, thought that the essential characteristic of life is having a soul (psychê). In common with other ancient writers, he used the term to mean the principle of living things that causes them to function as a living thing. He thought the soul was composed of fire atoms, because of the apparent connection between life and heat, and because fire moves.[8] He also suggested that humans originally lived like animals, gradually developing communities to help one another, originating language, and developing crafts and agriculture.[9] In the scientific revolution of the seventeenth century, mechanistic ideas were revived by philosophers like Descartes.

toHylomorphism is the theory (originating with Aristotle (322 BC)) that all things are a combination of matter and form. Aristotle was one of the first ancient writers to approach the subject of life in a scientific way. Biology was one of his main interests, and there is extensive biological material in his extant writings. According to him, all things in the material universe have both matter and form. The form of a living thing is its soul (Greek 'psyche', Latin 'anima'). There are three kinds of souls: the 'vegetative soul' of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation; the 'animal soul' which causes animals to move and feel; and the rational soul which is the source of consciousness and reasoning which (Aristotle believed) is found only in man.[10] Each higher soul has all the attributes of the lower one. Aristotle believed that while matter can exist without form, form cannot exist without matter, and therefore the soul cannot exist without the body.[11]

playConsistent with this account is a teleological explanation of life. A teleological explanation accounts for phenomena in terms of their purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. The direction of causality is the other way round from materialistic science, which explains the consequence in terms of a prior cause. Most modern biologists now reject this functional view in terms of a material and causal one: biological features are to be explained not by looking forward to future optimal results, but by looking backwards to the past evolutionary history of a species, which led to the natural selection of the features in question.

withVitalism is the belief that the life-principle is essentially immaterial. This originated with Stahl, and held sway until the middle of the nineteenth century. It appealed to philosophers such as Henri Bergson, Nietzsche, Wilhelm Dilthey, anatomists like Bichat, and chemists like Liebig. Vitalism underpinned the idea of a fundamental separation of 'organic' and inorganic material, and the belief that organic material can only be derived from living things. This was disproved in 1828 when Wöhler prepared urea from inorganic materials. This so-called Wöhler synthesis is considered the starting point of modern organic chemistry. It is of great historical significance because for the first time an organic compound was produced from inorganic reactants. Later, Helmholtz, anticipated by Mayer, demonstrated that no energy is lost in muscle movement, suggesting that there were no vital forces necessary to move a muscle. These empirical results led to the abandonment of scientific interest in vitalistic theories, although the belief lingered on in non-scientific theories such as homeopathy, which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force.

myIt is still a challenge for scientists and philosophers to define life in unequivocal terms.[12][13][14] Any definition must be sufficiently broad to encompass all life with which we are familiar, and it should be sufficiently general that, with it, scientists would not miss life that may be fundamentally different from earthly life.[15] Biology

pspHomeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature. Organization: Being structurally composed of one or more cells, which are the basic units of life. Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life. Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter. Adaptation: The ability to change over a period of time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion, for example, the leaves of a plant turning toward the sun (phototropism) and by chemotaxis. Reproduction: The ability

wannaTo reflect the minimum phenomena required, some have proposed other biological definitions of life: Living things are systems that tend to respond to changes in their environment, and inside themselves, in such a way as to promote their own continuation.[17] A network of inferior negative feedbacks (regulatory mechanisms) subordinated to a superior positive feedback (potential of expansion, reproduction).[18] A systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Variations of this definition include Stuart Kauffman's definition as an autonomous agent or a multi-agent system capable of reproducing itself or themselves, and of completing at least one thermodynamic work cycle

joinViruses are most often considered replicators rather than forms of life. They have been described as "organisms at the edge of life",[20] since they possess genes, evolve by natural selection,[21] and replicate by creating multiple copies of themselves through self-assembly. However, viruses do not metabolise and require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic molecules.[22][23

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Confucianism