Evolutionary species and their delimitation.

Ana Marcela Florez Rueda

This document attempts to describe the evolutionary species concept and to provide criteria to delimit evolutionary species. The evolutionary species concept was first stated by Simpson in 1961 and restated by Wiley in 1981 as “An evolutionary species is a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate”. Following Hening1 evolutionary species are “logical individuals bounded by speciation events with origins, existence and ends” 1 , they have an origin by cladogenesis, undergo evolution by anagenesis, and disappear by extinction. There has to be a “correlation with the species and the number of cladogenetic events that have occurred during the course of descent within a clade”1, this definition ties species to speciation and seeks for process, “divorcing species from cladogenesis destroys de distinction between tokogeny (nonhierarquical descent) and phylogeny ( hierarquical descent)”1 and this distinction is one of the premises of phylogenetic analysis.

The species problem involves different questions one is the species concept per se (an idea of what kind of entity species are) and the other is the operational question (a methodological approach to recognizing species in a particular case)2. Several authors1,2,3 have argued for the distinction of these two questions considering it the root of the “species problem”. Operational concepts (that try to answer both questions at once) are not universal because all operational species criteria will fail in some cases3 due to missing data, or simply inapplicability, consider the biological criteria of reproductive isolation, it is not applicable to asexual species, and sometimes it is impossible to determine. But the operational question is indeed the most important and accurate operational methods are a necessity. The ESC does not provide a method for the delimitation of species, but based on it one can choose the right method to delimit evolutionary species, there is plenty of empirical data and methods that can be brought to the question of whether a group of specimens is worthy of being hypothesized as parts of an evolutionary species, and when we consider this we can see the links between this concept and other species concepts.

The operational concepts must be reinterpreted as delimitation criteria. There are more than 20 species concepts which may have a delimitation criteria, each one of them should be evaluated to see if the species that delimits are evolutionary species, here I will only evaluate four species concepts/delimitation criteria. Biological delimitation agrees with the ESC because it proves lineage independence and identity, in the few cases when this kind of data is available it should be the primary criteria, but this is as previously stated a non universal delimitation criteria, and probably the less applicable, discerning potential reproductive barriers can be difficult, time consuming, expensive, and fraught with error. Homology and genealogical concordance are delimitation criteria that agree with ESC these are embodied in the PSC (sensu Mishler and Theriot), and GSC (sensu Baum and Shaw), they take into account the process of cladogenesis, and prove lineage independence, contrary to biological delimitation this methodology is widely applicable to all the taxa and there is a lot of data available. Delimitation criteria based on PSC (sensu Wheeler and Platnick) might result in every diagnosable subpopulation be called a species ignoring its genealogy, with terminals that may have tokogenetic relationships, making the delimited species unuseful for phylogenetic analysis, this approach is at odds whit the ESC, and thus prohibited.

The ESC provides an universal idea of what The Species is, but accurate operational methods are a necessity, hopefully biologist are now in a position to shift its attention away from the endless debate about the definition of The Species and “focus instead on estimating accurately the boundaries and numbers of species and studying the diverse processes involved in their origin and maintenance”. 2

Bibliography

1. Wheeler, Q. D. and Meier, R. (Editors). 2000. Species Concepts and Phylogenetic Theory: A Debate. New York: Columbia University Press.

2. de Queiroz, K. 2005. Different species problems and their resolution. Bioessays 27:1263-1269.

3. Wiens, J. J., and M. R. Servedio. 2000. Species delimitation in systematics: inferring diagnostic differences between species. Proceedings of the Royal Society of London, Series B 267:631–636.

THE SPECIES CONCEPTS IN AVES
Sergio David Bolívar Leguizamón
Biology
UIS

The number of species in Aves is 9000 to 10000 approximately. Within the group, there is clinal variation and populations intergradation. The Aves were identified by ornithologists using general morphology and patterns of coloration in the feathers. This Tipological Species Concept (TSC) were used to delimit and to recognize species in many groups. However, the TSC was used to identify and delimited species in Aves indiscriminately, but the TSC is not useful to identify sibling species and groups with sympatric populations.
Since Dobzhansky (1937) and Mayr (1952), the Biological Species Concept (BSC) has been used by ornithologists, the BSC claims that a species are groups of interbreeding natural populations that are reproductively isolated from other such groups. The geographic and reproductive isolation is the criterion of delimitation in th BSC. The sympatric species are defined as subspecies by BSC. The Aves posees great quantity of subspecies, because your high polymorphism within a same species. Studies claims that the sympatric species o subspecies must be considered as “emergent species” (Mayr, 1963). Nevertheless, BSC is not applicable in the field camp, the reproductive isolation is not applicable the Aves. In laboratory conditions the breeding of much birds is not successful, and the hybrid species have the uncertainty of if they are on or two species, futhermore, the sympatric species are not easy to identify because the variation in the populations could be insignificant. In fact, the ornithologists used coloration patterns to recognize species of birds. So, genera and species are difficult to determine. However, the BSC is proclamed as the principal species concept in Ornithology.
Nevertheless, other alternatives were emerged, as The Phylogenetics Species Concept (Cracraft, 1983; Nixon & Wheeler, 1990), offers a new vision about species and the asumptions about them. PSC (sensu Cracraft, 1983) is based in recognition of characters and monophyly (ancestry-descent), the PSC (sensu Cracraft,1983) claims that the species must be reproductively cohesive and diagnosable. For Cracraft, the species concept has three key elements: Reproductive cohesion, diagnosability, and a criterion for ranking populations at the species-level. The PSC (sensu Cracraft, 1983) offers greater theorical ans empirical support that BSC.
In the Ornithology, the delimitation of subspecies is bounded to great debate and discusion, some researchs claims that the populational variation must be treated as polimorphisms within of a species, on the other hand, researchs states that the “subspecies” hierarchy is very important in the classification and use of taxa.
In field camp, there are several statistical methods to delimit species, the Amadon's rule or 75% rule claims that two populations belong to the same species if the 75% of individuals in a population A posses the same character (or character state) that the 99% of a population B (Amadon, 1949). This statistical method was used by Patton & Unitt (2002), Meijaard & Groves (2004), and Cicero & Johnson (2006). The 75% rule is defined to mean that before a population is given subspecific status at least 75% of the individuals comprising it must be separable from +99% of the individuals of all other populations of the same species which may overlap with it as regards the geographically variable characters (Amadon, 1949).
The Methodology is based in statistical analysis, where the presence of trait of interest is plotted in the population and this is calculated for the others populations, and the comparisons are made. The standard deviation and media are calculated for the traits or characters of the population, if the standard deviation is not enough among the characters of populations (75%), then the population are the same species. But if the differentiation among the two populations in a character is > that 75%, the character separates the two populations in two subspecies.
For characters that occur as separate states, such as presence or absence of a plumage pattern or mtDNA haplotype or clade, the test involves a simple contingency table analysis. For continuously varying, normally distributed traits, such as measurements of body size, the rule involves comparison of the two distributions via their means, standard deviations and the expectation of 75% non-overlap from a t-distribution.
It rule provides a quantitative method to evaluate distinctiveness and in which to make subspecies designations (Patten and Unitt 2002). Nevertheless, the 75% rule is not strict, because sample effects or data's nature. Other approach similar to Amadon's rule are the 99% rule that is based on the same argument.
At least in Aves and for morphological data (Patton & Unitt, 2002; Meijaard & Groves, 2004; Cicero & johnson, 2006), the Amadon's rule is a way to delimit species and subspecies in sympatric populations. However, molecular analysis apply this method are non-existence, or they are few.
The PSC (sensu Cracraft, 1983) is more applicable and useful that the BSC (Mayr, 1952). The subspecies must be vievew as polimorphic populations, where the populational variation must be significative to postule new subspecies. The Amadon's rule (75%) is ambiguous because is usseful with morpholgical traits, but it is not quite applicable in molecular caracteres.

Bibliography

• Amadon, D. (1949) The seventy-five per cent rule for subspecies. The Condor, 51, 250-158.

• Cicero, C. & Johnson, N.K. (2006) Diagnosibility of subspecies: Lessons from sage sparrows (Amphispiza belli) for analysis of geographic variation in birds. The Auk, 123, 266-274.

• Courtney, S.P., Blakesley, J.A., Bigley, R.E., Cody, M.L., Dumbacher, J.P., Fleischer, R.C., Franklin, A.B., Franklin, J.F., Gutiérrez, R.J., Marzluff, J.M., & Sztukowski, L. (2004) Scientific evaluation of the status of the Northern Spotted Owl. Scientific evaluation of the status of the northern spotted owl. Sustainable Ecosystems Institute, Portland, Oregon. 508 pp.

• Cracraft, J. (1997) Species concepts in systematics and conservation biology – an ornithological viewpoint. Species The units of biodiversity. Ed. Chapman & Hall, 325-339.

• Groves, C.P., Meijaard, E. (2005) Interspecific variation in Moschiola, the Indian chevrotain. The Raffles Bulletin of Zoology, 12, 413-421.

• Mayr, E. (2000) The biological species concept. Species concepts and phylogenetics theory, Ed. Columbia University Press, pp 17-29.

• Patten, M.A., & Unitt, P. (2002) Diagnosibility versus mean differences of sage sparrow subspecies. The Auk, 119, 26-35.

Virus Species: A Controversy

A virus is an infectious agent composed by a genomic nucleic acid covered by several protective layers. In 1991, the International Committee on Taxonomy of Viruses (ICTV) endorsed the following definition of virus species: a virus species is a polythetic class of viruses that constitute a replicating lineage and occupy a particular ecological niche(1). The rationale for applying the species concept in virology is that viruses are biological entities and not chemicals: they possess genes, replicate, specialize, evolve and occupy specific ecological niches. The virologists adopted its own concept because they assumed that the only legitimate species concept was that of biological species defined by sexual reproduction, gene pools and reproductive isolation(2). However, within the multiplicity of species definitions just a reduced number of virologists, if any, have kept in mind the application of the phylogenetic species concept (PSC) into the virology field. The goal of this document is to present some fails of the virological concept of species and to introduce the PSC as an alternative in this field.

Viruses are intracellular parasites and are tangible, concrete entities, located in space and time that can be handled experimentally. Some authors(1, 2, 3) have proposed that the virus species, on the other hand, are abstractions that exist only in the mind. They realize that all biological classifications are conceptual constructions created by researchers for the purpose of introducing order in the bewildering variety of biological objects. In the same way, they emphasize that the categories used for building a classification such as families, genera and even species are not found in nature but are abstractions invented by human minds and concludes that species are thus not objects that will ever be encountered by researchers in their handling of viruses. It looks that those authors don't distinct between the species category within the Linnaean hierarchy of taxonomic categories and the taxon (group), that is ranked at the species level within that hierarchy. My interpretation aims to the view that species are concrete entities with a definite position in space and time rather than abstract classes with an indefinite origin in time; if we see species just as classes lead us to quite arbitrary decisions for their diagnose.

The virological definition of species means that no single property can be used as a defining property of a virus species and highlights that the major advantage of defining species as polythetic classes is that it makes it possible to accommodate, within a species, individual viruses that lack one or other characteristic that would normally be considered typical of the species(1, 2). It seems that for the virologists is problematic to have an enormous number of species because they group as a species clearly differentiated viruses. As has been(4) stressed: if it is advisable to recognize every lineage characterized even by just a fixed mutation and the goal of distinguishing species is to thereby recognize the end-products of evolution, should we seek to suppress naming large numbers of species where large numbers of differentiated end-products exist?. It have been have mentioned(1, 2) that it is the inherent variability of the members of a virus species that prevents a single discriminating character such a certain percentage of genome sequence dissimilarity to be used as a valid criterion for defining a species; instead of that percentage the virological concept of species proposes to use certain degree of properties similarity as is contemplate of what a polythetic class is (Each member possesses several of the diagnostic properties but no single defining property is present in all the members of the class). The PSC sensu Wheeler and Platnick define species as the smallest aggregation of (sexual) populations or (asexual) lineages diagnosable by a unique combination of character states(4); I deem that the use of percentages of similarity/dissimilarity will be rather arbitrary and irrational and that the PSC mentioned represents a unit species concept for all biological fields because is based on observable characters and avoids rampant subjectivity. Moreover, I consider that we do not create species as have been accentuated(2, 3); instead of it we identify and diagnose them by its character states.

On the other hand pair-wise sequence comparisons (PASC) have been used to produce multimodal distributions where the peaks are usually equated with clusters of sequences corresponding to groups of viral strains, species and genera(3). I consider that such PASC are just useful for delineating clusters of viruses but not to delineate species. The nucleotide sequences similarity percentages shows that, similarity, but we cannot expect to diagnose that two viruses belong to the same specie because of theirs nucleotide/amino-acid sequence identity degree. Furthermore, PASC on their own cannot provide clear cut quantitative criteria for distinguishing between different clusters and the clusters value percentage changes in different families. Consequently a level of genome homology fails to establish membership in a species.

PSC are recognized by unique combinations of constantly distributed characters and it’s compatible with phylogenetic theory because speciation events are marked by character transformations. It is a concept that applies equally to all conceivable speciation processes and biological entities (including viruses), representing a unit species concept. It aims to recognize the end-products of evolutionary processes and units of formal scientific nomenclature and as a final point the PSC concept meets the main requirement placed upon the species in virology: to achieve some rational order whereby some viral agents are grouped together.


References

1. Van Regenmortel, M.H.V. and Mahy, B.W.J., 2004. Emerging issues in virus taxonomy. Emerg. Infect. Dis. 10, 8–13.
2. Van-Regenmortel, M.H.V., 2007. Virus species and virus identification: Past and current controversies. Infection Genetics and Evolution 7(1): 133-144
3. Van Regenmortel, M.H.V., 2003. Viruses are real, virus species are man-made taxonomic constructions. Arch. Virol. 148, 2481–2488.
4. Wheeler, Q. D. and Meier, R. (Editors). 2000. Species Concepts and Phylogenetic Theory: A Debate. New York: Columbia University Press

Hempel’s General Ideas On Philosophy Of Science

Confirmation

The paradox of confirmation of the raven involves the confirmation of the generalization “all ravens are black” by an observation of something that satisfies the logical equivalent statement “all non-black things are non-ravens”, like a red apple, or a white handkerchief . These consequences are paradoxical, but Hempel argues, they must be accepted as valid. My point is that even something satisfies the two conditions non-black non raven it isn’t a confirmation of the generalization “all ravens are black”, a fact may be consistent with the hypothesis or even be an instance of it, without being evidence for it.

Degree Of Confirmation

This concept reflects the assumption which might be called the statistical version of the principle of induction and implies that the relative frequencies observed in the ‘past’ will remain fairly stable in the ‘future’. What degree of confirmation shall be assigned to H on the basis of E? And is represented such as ‘dc (H, E)‘. If a fixed frequency distribution ∆ is given or hypothetically assumed, then it is possible to define the concept pr ( H, E, ∆ ) the probability of H relatively to E according to the distribution ∆, defining dc (H, E)= pr ( H, E, ∆ ). This is an empirical reconstruction of the concept of degree of confirmation On the basis of a given Evidence, we infer the optimum distribution ∆ and then assign to H, as its degree of confirmation the probability which H possesses relatively to E according to ∆ .

Science doesn’t aim al high probabilities, it aims at a high informative content, based on experience, a hypothesis may be very probable because it may tell us very little, a high degree of probability is not an indication of a confirmation it may be only low informative content. Other point in contrast with this confirmation view is that it's based almost exclusively on frequencies of observations, this leaves out many other considerations, such as the previous knowledge on the subject, and its role in confirming the hypothesis.

Hempel on Theories

Hempel defined a theory as :”a coherent, integrated set of statements containing: (1) internal principles, (2) bridge principles, and (3) an identifiable body of phenomena to be explained”

First we have a understood vocabulary, according to the phenomena we’ll be able to state some empirical laws We introduce a new vocabulary, the internal principles to state laws describing the phenomena. The bridge principles are introduced in order to explain our empirical laws which allow us to establish logical connections between statements cast in the vocabulary of our new theory and statements cast in our antecedently understood vocabulary.

Although I agree with Lakato’s proposal of Scientific Research Programs, these are composed of theories which are composed of principles and this arrangement that Hempel describes of theories seems appropriate and important because verisimilitude and fallibility are ideas that are applied to theories and cannot be applied to research programs, but are indeed necessary for the qualification of those into progressive or degenerating.

Scientific Explanation

To Carl Hempel, scientific explanation is an argument that offers reasons for a given phenomenon to happen. It has to satisfied three requirements: explanatory relevance, which means that the explanation “affords good grounds for believing that the phenomenon to be explained did, or does, indeed occur.” Testability, the statement explaining the phenomena must be open to empirical test, and the premises must contain a scientific law.

The set of premises that explains the phenomenon is called the explanans; the conclusion is the phenomenon to be explained and is called the explanandum, it can be a singular fact or a general law. There are two explanans subclasses; one contains sentences which state specific antecedent conditions, the other represent general laws.

Hempel’s claim is that (a) every correct scientific explanation conforms to either the Deductive-Nomological model, D/N or the Inductive-Statistical model, I/S and that (b) anything that conforms to either of these models is a correct scientific explanation . These two models have very similar conditions:

• The explanation must be a deductively valid argument in the D/N model, so that the explanans must entail the explanandum. In the I/S model, the explanandum follows from the explanans with high inductive probability.
• In the D/N model the law-like statements in the explanans state actual laws. In the I/S model the explanans must contain at least one statistical law.
• The explanans must have empirical content.
• The premises contained in the explanans must be true or highly confirmed by all the relevant evidence available.

• And in the case of the I/S model the law must be “maximally specific”.

The second condition is the one which primarily distinguish them, and is also the one which is more debatable, in the case of the DN-model laws and law-like statements are conceptions that limit the scope for explanation, and in the case of the I/S model the statistical laws seem to not be enough for a proper explanation, natural laws make an explanation more accurate instead statistical laws make explanations doubtful. Other fault in which the two models fail is that they don’t properly reflect causal connections, they leave out significant considerations about the role of causality in explanation.

Hempel believed that science evolved in a continuous manner. New theory did not contradict past theory, more comprehensive theory replaced compatible, older theory. Each successive theory's explanation was closer to the truth than the theory before. It was the truth, and the prediction and control that came with it, that was the goal of logical-empirical science. In his view of progress Hempel denies the fact that some theories that have been defeated are false, and are not included in the theories by which were defeated. I believed that science evolves making progress with respect to truth, that is discovering new facts, and making predictions, in this way I agree with Hempel’s view.

Feyerabend's critics

Feyerabend's papers

Within of papers of Feyerabend, the historical process are very important in the development of knowledge, the history is inherent to knowledge. The actual education “alienates” to individual and it suppress the progress of science. Further, the dominant society and influential groups delay the progress of science and knowledge. The best form of progress in the knowledge is the Anarchy. “For a changing universe and it without established conditions, diversity of theories and methods”. If we clung to this, we do looses other forms potentially “useful” of discovery and analysis. No all theories is quite certain (true), if we postulates new hypothesis and theories that “confirms” or increases the support of the theories already established, we explain about same things and we don't contribute to knowledge. What it does not explain the theory is the start point of new searches. New paths implies new terms (dialectic), thus he concluded that the knowledge must be acquired for pluralistic methodologies. The best method to make science is contrainductive (falsationism). Alternative hypothesis must be proposed and it must be contrasted. Many hypothesis are necessary for a major covering of the reality. The principle of consistency is debated. A theory not must be “confirmed”, it must be “contrasted” with other(s). Theories cannot be dogmas, they are denied or ignore hypothesis potentially falsifiying. Plurality of opinion is advisable for the objective knowledge. Also the critical view of past is main in the science. Not to the scientific chauvinism. In the search of knowledge is necessary the imagination and creativity, however, any statement or sentence cannot be taken as valid in the knowledge, it must be analysed carefully. Because the imagination and observations are linked to our senses (subjective), we must be create new conceptual frameworks to analyze the phenomena and data, about this, he stated that the concepts are related to theories that explain them. The phenomena in reality are linked to their conceptual framework and they can mean different according to a particular view point (Feyerabend, 1965). Feyerabend postulated that is possible to make science “without experience” (1969), however, it does not possible because the data always are linked to experience (historical or sensitive). Thus, Paul Feyerabend proposed a plurality of opinion in the search of knowledge; but with a contrastation of theories and hypothesis sensu Lakatos. In his book Against the method (1975), Feyerabend claims for a “anarchy” in the science, nevertheless, he assume that the best form to acquire knowledge is the contrastation of theories, this goes against which it proposes.

Trough his life, Feyerabend modified many of his affirmations in their papers, therefore, he stated different and contradictory affirmations and ideas which were reformulated after, among they the science without experience and the importance of creativity and imagination. About this, he wrote after in 1987 (Critical Inquiry): “The conceited view that some humans beings, having the divine gift of creativity, can rebuild creation to fit their fantasies without consulting nature and without asking the rest of us, has not only led to tremendous social, ecological, and personal problems, it also has very doubtful credentials, scientifically speaking.” However, his perspective about the philosophy of science is valid because it always will be linked to historical process and political prejudices, etc. Without the history we does not develop knowledge and it is important in the explication of the world (which is historical).

In the history, the different events influences of the individual's life and groups of research. To Feyerabend, it was important because the sociological phenomena press the science to search new paths towards the knowledge. He critics hardly the institutions and methodologies which denies the diversity of opinion and those that delay the “progress” too. I agree with Feyerabend in these ideas because those situation happened in the scientific world.

Paul Karl Feyerabend (January 13, 1924 to February 1994) was philosopher of science best known for his work as a professor of philosophy at the University of California, Berkeley, where he worked for three decades (1958-1989). His major works include Against Method (published in 1975), Science in a Free Society (published in 1978) and Farewell to Reason (a collection of papers published in 1987). Feyerabend became famous for his purportedly anarchistic view of science and his rejection of the existence of universal methodological rules. He is an influential figure in the philosophy of science, and also in the sociology of scientific knowledge.

Historicity of Science

The “essay” does not have quotations to make the reading easier, but at the end is the bibliography read for writing this.

Popper on 1982 on his book realism and the aim of science tells us that a method of looking for verifications, it’s a typical method of a pseudoscience, and it is clearly different and distinguishable from the method of testing a theory as severely, that is the method of criticism, the method of looking for falsifying instances. If we accept this, the astronomers that look for new stars or that work specifying their distances, are not scientists; but the people that look for falsifying instances for the Chinese zodiac are. Opposite to this, Kuhn shows us that the problem of demarcation is not really a problem, but a product of the human idiosyncrasy; that is why we recognize some problems as scientific while others not depending on the prevailing paradigm. So we could say that the paradigm is what identifies a field of science.

There are two typical parts in science, one of Normal Science and one of crisis. The first one is characterized by past realizations accepted by a community (as a paradigm), for some time, as fundamental for the posterior practice. While normal science could be alone for long time periods, the crisis needs the existence of a paradigm to the emergent theories compete with. Crisis is always prowling around the research, because every problem that normal science sees as a puzzle can be seen, from another perspective, as a counter instance and thus a source of crisis. To my point of view what is important here is how strong and at the same time flexible is the paradigm to support and let the phenomenon being explain with the construct on hand.

The Normal Science focuses its investigation on three principal points. (i)The events that the paradigm has shown as particularly revealing of the things in nature, (ii) the predictions, and (iii) the empirical work undertaken to clear or articulate the theory of the paradigm. During this time the researchers design experiments and technology looking for better measures, and most important the predictions done around the paradigm. This part of the science is important because we need a theoretical body, which allows us to select and evaluate our researches.

The crisis starts with the discovering of a new sort of phenomenon (anomalies), this is a complex process which involves recognizing that something is and what it is. The first is to recognize that something has gone wrong in ways that may prove consequential. But anomalies do not emerge from the normal course of scientific research until both instruments and concepts have developed sufficiently to make their emergence likely and to make the anomaly which results recognizable as a violation of expectation. The second part is the struggle to make the anomaly law-like (because of the slant to physics of Kuhn, I think it could be used theory better). This period demands additional observation or experimentation as well repeated cogitation; while it continues scientists repeatedly revise their expectations, usually their instrumental standards, and sometimes their most fundamental theories as well.

When we are sure that we have an anomaly (unexpected discovery), we need a new vocabulary and new concepts for analyzing events. These new terms made the theories incomparable and the only criteria that could be used to choose between them is what and how they explain about the phenomena interest us.

The crises are resolved in one of three ways. Normal science can prove capable of handing the crisis provoking a problem; that is explaining from the paradigm or pasting to it. Alternatively, the problem resists and is labeled, but it is perceived as resulting from the field’s failure to possess the necessary tools with which it solve it, and so scientists set it aside for a future generation with more developed tools. In a few cases, a new candidate for paradigm emerges, and a struggle over its acceptance ensures; when the new paradigm is accepted and the other abandon a Revolution born. I think there could be another scenario in which the battle does not end in the death, absorbance or postpone of one theory, but the maintenance of both as different research programs or as a very long struggle.

The success of a paradigm is at the beginning a successful promise distinguishable in selected examples and still uncompleted. The Normal Science it about the promise achieve, expanding the knowledge and the facts that the paradigm shows as particularly interesting and revelators, incrementing the fitting extension between the events and the predictions of the paradigm.

The important thing to me about Kuhn thinking is no the Historical Structure of Science, or the importance of the revolution, its that clarify us that we need a conceptual body to develop the knowledge, and it is not as Popper said a process of trial and error, but a process of check and recheck.


- Kuhn T. 1962. Historical Structure of Scientific Discovery. Science 136: 760-764.
- Kuhn T. 1982. Commensurability, Comparability, Communicability. Proceedings of the Biennial Meeting of the Philosophy of Science Association 2: 669-688.
- Kuhn T. 1962. La estructura de las Revoluciones científicas.
- Popper K. 1982. Realism and the Aim of Science.

Methodology of Scientific Research Programs

Imre Lakatos, 1978

An adequately rational reconstruction of science has to evaluate as scientific not a single theory but instead of it a group of interrelated theories; Lakatos called them scientific research programs, which are composed of a conventionally accepted ‘hard core’ of interacting theories and a ‘belt’ of protective auxiliary hypotheses, and proposed the sophisticated falsationism as a criterion to select between rival programs. I agree with that methodology and I am going to present some reasons to support this position.

First at all, the statements which are inconsistent with the program can not defeat it. The program has a heuristic that allows us to save the program: we modify the belt without changing the hardcore; in this way, we can always reconcile the theories and the factual propositions. With sufficient resourcefulness and some luck, we can defend any program for a long time, even if it is false. Mere ‘falsifications’ must not imply rejection; they are to be considered –to convert them in corroborating examples- but need not be acted upon. The pattern of trial –by hypothesis- and error –shown by experiment-, is to be abandoned because no experiment is crucial to defeat a program.

Due to the fact that a program can not be defeated by the anomalies, the only way to decide when to abandon a program is the construction of a better one, which means that it has an excess empirical content over its predecessors, some of which is subsequently verified. As a consequence of this we have rival programs. If a program explains more than the rival, the latter will be falsified; therefore, the falsationism –a sophisticated one- requires competing programs. The competition is significant and leads to a rational reconstruction of scientific change in which each rival try to increase its content and predict novel facts. On the other hand, no advantage for one side can ever be regarded as absolutely conclusive; a novel belt of auxiliary hypotheses can strengthen a program. Consequently, the heuristic allows us to continue working in a program, as a positive outcome of that we won’t reject a program if the anomalies take place, giving us the opportunity to look at the potential of it.

Even though we can modify the belt of auxiliary hypotheses, there is a difference between the scientific modifications and the pseudoscientific ones that we make. A research program is said to be progressing –and therefore scientific- as long as its theoretical growth anticipates its empirical growth, that is, as long as it keeps predicting novel facts with some success. Conversely, a research program is said to be degenerating –and consequently, pseudoscientific- if it gives only a reinterpretation –a linguistic one- of facts anticipated, and discovered in a rival program. According to this methodology the greatest scientific achievement are research programs which can be evaluated in terms of progressive and degenerating problem shifts.

Another fundamental point is that the methodology of scientific research programs has a historical character. If we wan to follow this methodology and develop a scientific program we will look in history for rival research programs and if instead of it we want to explain different speeds of development of different research program we may need to invoke external history. Moreover, the scientific revolutions along the history are shifts of one program over another.

We need a lot of time to evaluate a research program, but this evaluation is stricter because it requires that the belt of auxiliary hypotheses –following a positive heuristic- turn into a progressive shift and predicts novel facts. The methodology of research programs, finally, emphasizes long-extended theoretical and empirical competition of major research programs, progressive and degenerating problem-shifts, and the slowly emerging victory of one program over the other.