Gradualism and The Conception of Species as Classes or Sets Rather Than Individuals
- Pages: 7
- Word count: 1716
- Category: Theories
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The theory of gradualism which is also called phyletic gradualism is the concept that evolution occurs in a gradual way with small changes that accumulates through time. The concept of gradualism is contradictory to punctualism. Punctualism on the other hand is the idea that evolution happens in a very abrupt and rapid way which is soon followed by long period of stagnation where no evolutionary changes occur. Punctualism is based on the various interpretations that evolutionary biologists get from the fossil records whereas; the gradualism theory is based primarily on the population genetics theory. Nevertheless, most contemporary evolutionary biologists would view the two theories as non-contradictory, since gradual genotypic changes would ultimately lead to major changes in an organism’s phenotype (appearance).
In close relationship with the concepts of gradualism and puctualism is the 1972 theory by Stephen Gould and Niles Eldredge which stated that the idea of punctuated equilibrium is in fact a way to explain the lack of continuity and intermediate steps in fossil records. According to this two evolutionary biologists they pointed out that any biological species cannot go through a gradual process of evolution rather they went into a state of stable and undisturbed equilibrium wherein there is slow evolution or no evolution at all, and then this long equilibrium is followed by a very quick burst of evolution that results to the formation of a new species. They also added up that some evolutionary changes do not happened as a result of adaptation, but other occur at the level of the species.
Speciation is the process in evolution that results to the formation of a new species. There are still ongoing debates as to the major processes the backs up the idea of speciation, whether it is achieved through genetic drift or through Charles Darwin’s proposal on natural selection. In nature, there are four major ways wherein speciation occurs which are closely based on the concept of geographical isolation. These are allopatric, sympatric peripatric, and parapatric modes of speciation. Currently, speciation is also induced artificially through the process of animal husbandry.
Allopatric speciation occurs when there are sudden geographical changes that caused a population to be isolated from each other and while being isolated they undergo both genotypic and phenotypic changes. After being reunited through various mechanical events, they become different and may not be able to reproduce. Peripatric speciation on the other hand is related to the concept of founder’s effects where small peripheral members of the population are prevented form exchanging genes with each other. And lastly, parapatric speciation there is only partial separation between the species and there are still contacts between them, yset this partial separation reduces fitness (ability to interbreed and produce viable offsprings)
In the recent years, biologists had a hard time categorizing the traits that occur in all and in some members of the species. As cited by Hulls he pointed out that there are few forces that act against the universality and the uniqueness in the traits of the members of the species; these forces are mutation, random drifts and recombination. When these forces act to a certain organisms or groups of organism, it affects the traits of these organisms hence, affecting his membership in that specific species. This left many evolutionary biologists with one of the oldest questions in science with is the species concept.
To start with, certain traits must occur in all members of a certain species, and then these traits become the essence of the species. But looking at the different organisms, there are organisms that shared common characteristics. For Hull, he cited that within species exists a vague boundary and these vague boundaries becomes incompatible due to the subsistence of important species specific essences. In addition to this, Hull argued that in order for something to have essentialist definition, there should be clear and strict boundaries between them and since the boundaries in species are vague (since the gradual changes that occur in a species would render no precise boundary between the one to the next). With this, a species cannot therefore be rendered essential definitions.
With this varying ways of qualifying the idea of species, there were notions that species are individuals and another pointed out that species are sets in the process of evolution. Identifying species needs theories, basis, foundations and even speculations and in trying to give light to the different theories and ideas behind them, one must first look at on the concept of ideas together and how they work with theories.
Using the empirical theory-ladenness arguments, psychological phenomenon are employed in order to show that observations are in the real sense “theory-laden”. But there were claims that observations labeled as “theory-laden” are ambiguous. There are three concepts behind the idea of theory-ladenness. First is that, in order for the observer to develop a casual view of a specific experiment and how to see if it fares to its relationship to a certain theory, one must to have a good grasp and overview of the theory. In Norwood Russell Hanson’s book entitled Patterns Of Discovery, he pointed out that “Observation of x is shaped by prior knowledge of x. Another influence on observations rests in the language or notation used to express what we know, and without which there would be little we could recognize as knowledge.”(Hanson 1958, 19)
There is also one notion of the laden-theory in science is that it is nothing more than a casual talk; he further stated that the effects and the connections between these talks are recognized. The laden-theory way of talking is different with the use of sense-datum language; he further maintains that sense-datum language lacks any casual meaning. For him, the only way that science maintains its goal is by acting with its casualty.
In the world of science according to Hanson, there are many perceptual accounts that are free from any theory; he called this as other phenomena that have no use in science because having a phenomenal nature would make them free from any sorts of explanatory contents.
Species as Individuals
Ghiselin and Hull suggested that a species is an “individual” and not as “natural kinds”. For Hull he created an ontological distinction between the terms “natural kinds” and the word “class”. For them the term “classes” are groups of entities or individuals that function and act under a specific scientific law. In addition to that this scientific law has it that these classes are true and at any place in the universe and at any time. On the other hand, individuals are made up of parts that are spatiotemporally constrained. For example, the parts of an organism cannot exist at different places and at different times, they have to function as a whole in the same space and time. To sum up again, individuals are spatiotemporally limited while classes are spatiotemporally free.
Therefore given their definition of classes and individuals, they argue that species were in fact species and not classes. There is a contention in the Evolutionary Unit Argument that states that species are units of evolution. But species being a unit does not mean there is merely a change in the gene frequencies in a specific species from one generation to the other, rather the significance of this unit lies on how a certain trait becomes rare to prominent in a species. These evolutionary biologists explained that natural selection is a process by which a trait becomes prominent in a gene pool. Selection involves reproduction which on the other hand strictly requires and organism to be spatiotemporally limited in order to reproduce. Therefore, if these species are in fact units in evolution they should be considered as individuals and not as units.
There are major implications for the notion that species are individuals, firstly organisms and species is not a member-class relationship but a part and whole relationship. Hence, an organism is a part of a specific species if it can fit in the causal connections to the other organisms grouped under that the same species as well.
Another implication that comes from the basis of “individual” and “class” applies on evolution itself. An organism belongs to a certain species if it has been a part of the evolving lineage. If the idea of belonging to as species is only as a result of the organism’s insertion in the lineage, then the whole concept becomes misleading. There might be organisms that appear very similar to each other may it be genetically, morphologically, and behaviorally, but unless they are part of the same organizations that existed spatiotemporally in the same lineage, then they cannot be called the same in species level.
Species as Set
Contrary to the concept of Hull and Ghiselin, Kitcher in 1984 believes that species are in fact sets of organisms. He argued that the claim that species are to be considered as an individual would also mean that these biologists took a neutral ontological stance where some species are spatiotemporally limited while the others are not.
In the explanation of Ernst Mayr Kitcher, he argued that there are two basic types of explanation in biology. These two explanations are the proximate cause and the ultimate causes. When one say proximate explanations then it gives focus on the immediate cause for a trait e.i the genes that caused these changes. On the other hand, ultimate explanations are more on the evolutionary explanations on why things exist.
He further argued that the concept of species can be defined according to these fundamental explanations in biology. The proximate explanation suggests that “species concept” is based on the genetic, developmental and chromosomal similarities of these species and organisms. While on the other hand, ultimate explanations give the species its evolutionary roles.
Ghiselin, M., “Species Concepts, Individuality, and Objectivity”, Biology and Philosophy, 2:127-143. 1987.
Hull, D., “A Matter of Individuality”, Philosophy of Science, 45:335-360. 1987.
Mishler, B. and Donoghue, M., “Species Concepts: A Case for Pluralism”, Systematic Zoology, 31: 491-503. 1982.
Reydon, T., “Species Are Individuals Or Are They?” Philosophy of Science, 70: 49-56. 2003.