Richard Levins - Collected Quotes

"A mathematical model is neither an hypothesis nor a theory. Unlike the scientific hypothesis, a model is not verifiable directly by experiment. For all models are both true and false. Almost any plausible proposed relation among aspects of nature is likely to be true in the sense that it occurs (although rarely and slightly). Yet all models leave out a lot and are in that sense false, incomplete, inadequate. The validation of a model is not that it is 'true' but that it generates good testable hypotheses relevant to important problems. A model may be discarded in favor of a more powerful one, but it usually is simply outgrown when the live issues are not any longer those for which it was designed." (Richard Levins, "The Strategy of Model Building in Population Biology", American Scientist 54(4), 1966)

"For population genetics, a population is specified by the frequencies of genotypes without reference to the age distribution, physiological state as a reflection of past history, or population density. A single population or species is treated at a time, and evolution is usually assumed to occur in a constant environment. Population ecology, on the other hand, recognizes multispecies systems, describes populations in terms of their age distributions, physiological states, and densities. The environment is allowed to vary but the species are treated as genetically homogeneous, so that evolution is ignored." (Richard Levins, "The Strategy of Model Building in Population Biology", American Scientist 54(4), 1966)

"It is of course desirable to work with manageable models which maximize generality, realism, and precision toward the overlapping but not identical goals of understanding, predicting, and modifying nature. But this cannot be done. Therefore, several alternative strategies have evolved: (1) Sacrifice generality to realism and precision. (2) Sacrifice realism to generality and precision. (3) Sacrifice precision to realism and generality." (Richard Levins, "The strategy of model building in population biology", American Scientist Vol. 54 (4), 1966) 

"The multiplicity of models is imposed by the contradictory demands of a complex, heterogeneous nature and a mind that can only cope with few variables at a time; by the contradictory desiderata of generality, realism, and precision; by the need to understand and also to control; even by the opposing esthetic standards which emphasize the stark simplicity and power of a general theorem as against the richness and the diversity of living nature. These conflicts are irreconcilable. Therefore, the alternative approaches even of contending schools are part of a larger mixed strategy. But the conflict is about method, not nature, for the individual models, while they are essential for understanding reality, should not be confused with that reality itself." (Richard Levins, "The Strategy of Model Building in Population Biology", American Scientist 54(4), 1966)

"The validation of a model is not that it is 'true' but that it generates good testable hypotheses relevant to important problems." (Richard Levins, "The Strategy of Model Building in Population Biology", American Scientist 54(4), 1966)

"[…] truth is the intersection of independent lies." (Richard Levins, "The Strategy of Model Building in Population Biology", 1966)

"Unlike the theory, models are restricted by technical considerations to a few components at a time, even in systems which are complex. Thus a satisfactory theory is usually a cluster of models. These models are related to each other in several ways : as coordinate alternative models for the same set of phenomena, they jointly produce robust theorems; as complementary models they can cope with different aspects of the same problem and give complementary as well as overlapping results; as hierarchically arranged 'nested' models, each provides an interpretation of the sufficient parameters of the next higher level where they are taken as given." (Richard Levins, "The Strategy of Model Building in Population Biology", American Scientist 54(4), 1966)

"All evolutionary theories, whether of physical, biological, or social phenomena, are theories of change. The present state of a system is seen as different from its past states, and its future states are predicted to again differ from the present. But the simple assertion that past, present, and future differ from one another is not in itself an evolutionary world view." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"Parts and wholes evolve in consequence of their relationship, and the relationship itself evolves. These are the properties of things that we call dialectical: that one thing cannot exist without the other, that one acquires its properties from its relation to the other, that the properties of both evolve as a consequence of their interpenetration." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"The concept of adaptation implies that there is a preexistent form, problem, or ideal to which organisms are fitted by a dynamical process. The process is adaptation and the end result is the state of being adapted. Thus a key may be adapted to fit a lock by cutting and filing it, or a part made for one model of a machine may be used in a different model by using an adaptor to alter its shape. There cannot be adaptation with out the ideal model according to which the adaptation is taking place. Thus the very notion of adaptation inevitably carried over into modern biology the theological view of a preformed physical world to which organisms were fitted." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"The large-scale computer models of systems ecology do not fit under the heading of holism at all. Rather they are forms of large-scale reductionism: the objects of study are the naively given 'parts' -abundances or biomasses of populations. No new objects of study arise at the community level. The research is usually conducted on a single system - a lake, forest, or prairie - and the results are measurements of and projections for that lake, forest, or prairie, with no attempts to find the properties of lakes, forests, or prairies in general. Such modeling requires vast amounts of data for its simulations, and much of the scientific effort goes into problems of estimation." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"The organism cannot be regarded as simply the passive object of autonomous internal and external forces; it is also the subject of its own evolution." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"Things are similar: this makes science possible. Things are different: this makes science necessary. At various times in the history of science important advances have been made either by abstracting away differences to reveal similarity or by emphasizing the richness of variation within a seeming uniformity. But either choice by itself is ultimately misleading. The general does not completely contain the particular as cases, but the empiricist refusal to group, generalize, and abstract reduces science to collecting - if not specimens, then examples." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"We believe that science, in all its sense, is a social process that both causes and is caused by social organisation." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

"We can hardly have a serious discussion of a science without abstraction. What makes science materialist is that the process of abstraction is explicit and recognized as historically contingent within the science. Abstraction becomes destructive when the abstract is reified and when the historical process of abstraction is forgotten, so that the abstract descriptions are taken for descriptions of the actual objects. The level of abstraction appropriate in a given science at a given time is a historical issue." (Richard Levins & Richard C Lewontin, "The Dialectical Biologist", 1985)

On Heuristics: Trial and Error in Biology

"Higher organisms are able to learn through trial and error how a certain problem should be solved. We may say that they too make testing movements - mental testings - and that to learn is essentially to tryout one testing movement after another until one is found that solves the problem. We might compare the animal's successful solution to an expectation and hence to a hypothesis or a theory. For the animal's behaviour shows us that it expects (perhaps unconsciously or dispositionally) that in a similar case the same testing movements will again solve the problem in question." (Karl R Popper, "The Logic and Evolution of Scientific Theory", [in "All Life is Problem Solving", 1999] 1972)

"The natural as well as the social sciences always start from problems, from the fact that something inspires amazement in us, as the Greek philosophers used to say. To solve these problems, the sciences use fundamentally the same method that common sense employs, the method of trial and error. To be more precise, it is the method of trying out solutions to our problem and then discarding the false ones as erroneous. This method assumes that we work with a large number of experimental solutions. One solution after another is put to the test and eliminated." (Karl R Popper, "The Logic and Evolution of Scientific Theory", [in "All Life is Problem Solving", 1999] 1972)

"Whatever the system, adaptive change depends upon feedback loops, be it those provided by natural selection or those of individual reinforcement. In all cases, then, there must be a process of trial and error and a mechanism of comparison. […] By superposing and interconnecting many feedback loops, we (and all other biological systems) not only solve particular problems but also form habits which we apply to the solution of classes of problems." (Gregory Bateson, "Steps to an Ecology of Mind", 1972)

"When we examine this suggestion, we see that it is no more than a formal acknowledgement of a problem, the problem of how (by what institutional arrangement, by what organization of affairs) the equilibrium prices are to be discovered. Repeated trial and error, while the market stands in suspense awaiting the outcome, is not a practical resort. The number of distinct trials, even if confined to discrete steps of price and quantity, would be so immense that the necessary 'market day' would extend beyond human life-times [... The] theoretical ideal applies to mutually isolated days or moments, each to be treated as perfectly self-contained and looking to no yesterday and no tomorrow. But the real market is dealing with goods inherited from yesterday, and in means of production whose products will not be ready till tomorrow. Meanwhile the non-economic circumstances are changing and rendering each successive equilibrium obsolete." (George L S Shackle, "Epistemics and Economics", 1972)

"We know the laws of trial and error, of large numbers and probabilities. We know that these laws are part of the mathematical and mechanical fabric of the universe, and that they are also at play in biological processes. But, in the name of the experimental method and out of our poor knowledge, are we really entitled to claim that everything happens by chance, to the exclusion of all other possibilities?" (Albert Claude, "The Coming Age of the Cell", Nobel Prize Lecture] 1974)

"Survival machines that can simulate the future are one jump ahead of survival machines that who can only learn of the basis of trial and error. The trouble with overt trial is that it takes time and energy. The trouble with overt error is that it is often fatal. [...] The evolution of the capacity to simulate seems to have culminated in subjective consciousness. Why this should have happened is, to me, the most profound mystery facing modern biology." (Richard Dawkins, "The Selfish Gene Source: The Selfish Gene", 1976)

"In the process of the evolution of life, as far as we know, the total mass of living matter has always been and is now increasing and growing more complex in its organization. To increase the complexity of the organization of biological forms, nature operates by trial and error. Existing forms are reproduced in many copies, but these are not identical to the original. Instead they differ from it by the presence of small random variations."  (Valentin F Turchin, "The Phenomenon of Science: A cybernetic approach to human evolution", 1977)

"I believe people can solve complex problems eventually. By repeated trial and error they will get there; but they need a long time. At this point I agree with Herbert Simon. People do not learn immediately, as those rational expectations models seem to imply. I don't believe that. The statement that assumptions do not matter is nonsense. It is funny. Yes, I assume people are consistent in their behavior. I assume that not because I believe everybody actually is, but because I believe, on the average, you do not get too far from it." (Franco Modigliani, "Conversations with Economists", 1983)

"Heuristics are rules of thumb that help constrain the problem in certain ways (in other words they help you to avoid falling back on blind trial and error), but they don't guarantee that you will find a solution. Heuristics are often contrasted with algorithms that will guarantee that you find a solution - it may take forever, but if the problem is algorithmic you will get there. However, heuristics are also algorithms." (S Ian Robertson, "Problem Solving", 2001)

Jacques Monod - Collected Quotes

"There are living systems; there is no living 'matter'. No substance, no single molecule, extracted and isolated from a living being possess, of its own, the aforementioned paradoxical properties. They are present in living systems only; that is to say, nowhere below the level of the cell." (Jacques Monod, "From Biology to Ethics", 1969)

"A totally blind process can by definition lead to anything; it can even lead to vision itself." (Jacques Monod, "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology", 1970)

"Among all the occurrences possible in the universe the a priori probability of any particular one of them verges upon zero. Yet the universe exists; particular events must take place in it, the probability of which (before the event) was infinitesimal. At the present time we have no legitimate grounds for either asserting or denying that life got off to but a single start on earth, and that, as a consequence, before it appeared its chances of occurring were next to nil. [...] Destiny is written concurrently with the event, not prior to it." (Jacques Monod, "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology", 1970)

"Even today a good many distinguished minds seem unable to accept or even to understand that from a source of noise natural selection alone and unaided could have drawn all the music of the biosphere. In effect natural selection operates upon the products of chance and can feed nowhere else; but it operates in a domain of very demanding conditions, and from this domain chance is barred. It is not to chance but to these conditions that evolution owes its generally progressive course, its successive conquests, and the impression it gives of a smooth and steady unfolding." (Jacques Monod, "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology", 1970)

"Every living being is also a fossil. Within it, all the way down to the microscopic structure of its proteins, it bears the traces if not the stigmata of its ancestry." (Jacques Monod, "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology", 1970)

"Evolution in the biosphere is therefore a necessarily irreversible process defining a direction in time; a direction which is the same as that enjoined by the law of increasing entropy, that is to say, the second law of thermodynamics. This is far more than a mere comparison: the second law is founded upon considerations identical to those which establish the irreversibility of evolution. Indeed, it is legitimate to view the irreversibility of evolution as an expression of the second law in the biosphere." (Jacques Monod, "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology", 1970)

"A curious aspect of the theory of evolution is that everybody thinks he understands it." (Jacques Monod, "On the Molecular Theory of Evolution", 1974)

"One of the great problems of philosophy, is the relationship between the realm of knowledge and the realm of values. Knowledge is what is; values are what ought to be. I would say that all traditional philosophies up to and including Marxism have tried to derive the “ought” from the “is.” My point of view is that this is impossible, this is a farce." (Jacques Monod)

"The scientific attitude implies the postulate of objectivity - that is to say, the fundamental postulate that there is no plan; that there is no intention in the universe." (Jacques Monod)