What Is Life?

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What Hopkins offered instead was a view of the cell as a chemical machine, obeying the laws of thermodynamics and physical chemistry generally, but having organized molecular structures and functions. The chemistry underlying metabolism was catalyzed and regulated by enzymes, protein catalysts, and involved, because of biological necessity, small changes in structure and energy of well-defined chemical intermediates. Understanding how the organization was achieved was just as important as knowing how the chemical reactions occurred. A member of the department, Joseph Needham became actively engaged in carrying Hopkins's vision to the broader intellectual community writing on the philosophical basis of biochemistry Needham He followed Hopkins too in asserting that the crucial question no longer was the relationship of living and non-living substance but also of mind and body, with biochemistry conceding to philosophy and the then incipient neurosciences, the latter question, so that it could focus on learning about living matter.

What is life

Another member of the biochemistry department, N. There was a challenge for Hopkins's program to figure out how rather simple physical and chemical laws could produce the complexity of living systems. Bernal and Dorothy Crowford Hodgkins and philosophers J. Woodger and Karl Popper. This group was consciously exploring the philosophical approach of Whitehead with the goal of building a trans-disciplinary theoretical and philosophical biology which helped lay the foundation for the conceptual triumph of molecular biology after World War II Abir-Am ; de Chadarevian The research program of Hopkins was well established by this period and especially through the Needhams it was linked with the work of the Biotheoretical Gathering, influencing J.

Haldane, who made major contributions to enzymology and to forging the modern evolutionary synthesis or neo-Darwinism. Haldane, along with Bernal, would play a major, early role in moving the concern from beyond the nature of life to its origin as a subject for scientific study. Haldane suspected, along with Pirie, that a fully satisfactory definition of life was impossible, but he asserted that the material definition was a reasonable goal for science.

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This pattern has special properties. It begets a similar pattern, as a flame does, but it regulates itself as a flame does not. Use of the flame metaphor for cellular metabolic activity implied a nonequilibrium process in an open system capable of reproduction but also, by the limit of the metaphor, self regulation. In this Haldane reflected the shifting concern to working out how matter and physical laws could lead to biological phenomena. It was clear that there were several distinct ways in which matter in living systems behaved in ways different from non-living systems.

For example, how could genetic information be instantiated at a molecular level given that ensembles of atoms or molecules behaved statistically? Or, how could biological systems generate and maintain their internal order in the face of the imperative of the second law of thermodynamics that all natural systems proceed with increasing entropy?

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The problem of heredity then was reformulated at the molecular level as to how order could give rise to order? It was the answer to the first question that captured the attention of the founders of the new biology. By creating internal order and organization within a living system cells, organisms or ecosystems the metabolic activities must produce greater disorder in the environment, such that the second law is not violated. Knowledge about the protein and nucleic acid basis of living systems continues to be obtained at an accelerating rate, with the sequencing of the human genome as a major landmark along this path of discovery.

The world is divided into replicators, which are seen to be fundamental and to control development and be the fundamental level of action for natural selection, and interactors, the molecules and structures coded by the replicators Dawkins , Indeed, Dawkins relegates organisms to the status of epiphenomenal gene-vehicles, or survival machines. A reaction has set in to what is perceived as an over-emphasis on nucleic acid replication see for example Keller , ; Moss Prominent among early students of such nonequilibrium thermodynamics was Ilya Prigogine Prigogine influenced J.

Bernal in his lectures on the physical basis of life to start to understand both how organisms produced their internal order while affected their environment by not only their activities but through created disorder in it Bernal Harold Morowitz explicitly addressed the issue of energy flow and the production of biological organization, subsequently generalized in various ways Morowitz ; Peacocke ; Brooks and Wiley Wicken ; Schneider ; Swenson ; Morowitz The emergent, self-organizing spatio-temporal patterns observed in the Belousov-Zhabotinski reaction are also seen in biological systems such as in slime mold aggregation or electrical patterns in heart activity Tyson ; Sole and Goodwin Indeed, related self-organizational phenomena pervade biology Camazine et al.

Such phenomena are seen not only in cells and organisms, but in ecosystems, which reinforces the notion that a broader systems perspective is needed as part of the new physics Ulanowicz Important to such phenomena are the dynamics of non-linear interactions where responses of a system can be much larger than the stimulus and autocatalytic cycles reaction sequences that are closed on themselves and in which a larger quantity of one or more starting materials is made through the processes.

Such an approach non-reductively connects the phenomena of living systems with basic laws of physics and chemistry Harold Whether the existing sciences of complexity are sufficient or a newer conceptual framework is needed remains to be seen Harold Living beings exhibit complex, functional organization and an ability to become more adapted to their environments over generational time, which phenomena represent the challenge to physically-based explanations based upon mechanistic reductionistic assumptions. One of the biggest and most important of emergent phenomena is that of the origin or emergence of life.

Franklin Harold ranks the mystery of life's origin as the most consequential facing science today Harold , Michael Ruse claims that it is essential to incorporate origin of life resarch into Darwinism since it is a necessary condition for a scientifically and philosophically adequate definition of life Ruse , To answer this why question we need to understand how life might have arisen.

While not attracting the attention nor levels of funding of molecular biology, there was a continuous research program during much of the twentieth century on the origin of life for historical summaries see Fry ; Lahav During the s Alexander Oparin and J. In effect this type of approach can be termed a metabolism-first view. This protein-first view suggested that the chemistry that lead to life could have occurred in a sequestered environment globs of proteins that might also have some weak catalytic activity that would have facilitated the production of the other molecular components needed Fox With the understanding of the structure of DNA focus shifted to the abiotic routes to nucleic acids, which could serve then serve as templates for their own replication.

Variants of this approach represent the dominant mode of thinking about the early phases of the emergence of life Maynard Smith and Szathmary Given that some type of metabolism would be needed to sustain RNA replication, a number of approaches blend replication-first with metabolism-first Dyson , ; de Duve ; Eigen An alternative view, congenial to a thermodynamic and systems approach to the emergence of life, takes the above move a step further and emphasizes the need the presence of the main factors that distinguish cells from non-cells: metabolism via autocatalytic cycles of catalytic polymers, replication, and a physical enclosure within a chemical barrier like that provided by the cell membrane.

Chemical constraints and the self-organizing tendencies of complex chemical systems in such a view would have been critical in determining the properties of the first living beings. With the emergence of the first entities that could be termed living would come the emergence of biological selection or natural selection in which contingency plays a much greater part. Darwin famously bracketed the question of the origin of life from questions of descent with modification through natural selection.

Indeed, Darwinian theories of evolution can take living systems as a given and then explore how novelties arise through a combination of chance and necessity. However, an understanding of how life might have emerged would provide a bridge between our view of the properties of living systems and the evolutionary phenomena they exhibit. Such an understanding ultimately is needed to anchor living systems in matter and the laws of nature Harold , This remains a challenge to be met in order for science to provide a more full answer to Shelley's question.

There goal is to place life as it is known on earth in a larger conceptual context of any possible forms of life Langton , Work in A-Life shifts our focus on the processes in living things rather than the material constituents of their structures per se Emmeche In some ways this is a revival of the process thinking of the Cambridge biochemists of the s, but involves a level of abstraction about the material structures that instantiate these processes that they would not have shared.

A-Life studies can help us to sharpen our ideas about what distinguishes living from non-living and contribute to our definition of life. Such work can help delineate the degree of importance of the typical list of attributes of living entities, such as reproduction, metabolism, functional organization, growth, responsiveness to the environment, movement, and short- and long-term adaptations. A-Life work can also allow exploration about which features of life are due to the constraints of being enmattered in a particular manner and subject to physical and chemical laws, as well as exploring a variety of factors that might affect evolutionary scenarios Etxeberria For example, the relative potential roles of selection and self-organization in the emergence of novel traits in evolutionary time might be evaluated by A-Life research.

It is too soon yet to know how important the contribution of the A-Life program will be, but it is likely to become more prominent in the discourse on the origin and nature of life. Our increased understanding of the physical-chemical basis of living systems has increased enormously over the past century and it is possible to give a plausible definition of life in these terms. Much remains to be elucidated about the relationships among the complex molecular systems of living entities, how they are constrained by the system as a whole as well as by physical laws. Indeed, it is still an open question for some as to whether we have yet a sufficiently rich understanding of the laws of nature or whether we need to seek deep laws that lead to order and organization Kauffman Significant challenges remain, such as fully integrating our new view of organisms and their action with evolutionary theory, and to understand plausible routes for the emergence of life.

The fulfillment of such a program will give us a good sense of what life is on earth. Work in A-Life and empirical work seeking evidence of extra-terrestrial life may help the formulation of a more universal concept of life. The Biochemical Conception of Life 3. Origin Emergence of Life 6. Artificial Life 7. The Biochemical Conception of Life Perhaps the venue where the issue of the nature of life was most urgently addressed was the Department of Biochemistry at the University of Cambridge.

Origin Emergence of Life One of the biggest and most important of emergent phenomena is that of the origin or emergence of life. Conclusions Our increased understanding of the physical-chemical basis of living systems has increased enormously over the past century and it is possible to give a plausible definition of life in these terms. Bibliography Abir-Am, P. Benner, S.

What Is Life - Wikipedia

Bernal, J. Brooks, D. Bunge, M. Cairns-Smith, A. Camazine, S. Carroll, S. Dawkins, R. Weber and D. De Chadarevian, S.

Definitions of life

De Duve, C. Depew, D. Dyson, F. Eigen, M. Emmeche, C. Etxeberria, A. Fox, S. Fruton, J. Molecules and Life , New York: Wiley.

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Fry, I. Gayon, J. Origins of Life and Evolution of Biospheres , — Gilbert, W. Graur, D. Haldane, J. What is Life?

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What Is Life? What Is Life?
What Is Life? What Is Life?
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What Is Life? What Is Life?
What Is Life? What Is Life?
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