Explanation and conditional probabillity

When we throw a scientific question we’re search by answers with the maximum correction and that fit into more general explanatory models. Needless to say that these more general models must provide refutable structures. This allows that our ideas makes sense within a larger set of principles. One example is the idea of the evolution of species, although the species itself is a term which has caused some controversy. Initially Darwin suggested that:

“No one definition has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species. Generally the term includes the unknown element of a distinct act of creation. (Darwin, 1859)”

Later, Darwin revised his understanding of the matter more critically as follows:

“But it is a hopeless endeavor to decide this point on sound grounds, until some definition of the term “species” is generally accepted; and the definition must not include an element which cannot possibly be ascertained, such as an act of creation. (Darwin, 1871)”

Currently, the most of scientists support the concept of species proposed by Theodosius Dobzhansky(1937) and Ernst Mayr (1942).

“[…] as groups of interbreeding populations in nature, unable to exchange genes with other such groups living in the same area (Meyer, 2005)

Darwin seen in the concept of species a limitation from our perceptive abilities. For that, we perceive continuous events as discontinuous events. He still conceived the importance of use the term species to organization, but recognize a poverty philosophical view on the term. Nowadays, there’s sympathizers of the idea of continuity or gradation and others divergent from continuity’s idea between species to support the Mayr’s discontinuity idea.

I’ll not deepen on the discontinuity question. That little introduction just want address to the fact that discussion never is simplest as some people believe it is. The idea of evolution emerged as a candidate to explain the great diversity of living beings on Earth. Remarkable, was not Darwin the first to present evolution as an explanation. The idea of evolution refer to Erasmus Darwin (grandfather of Charles Darwin), Jean-Baptiste Lamarck and Étienne Saint-Hilaire, for example. Darwin appointed a mechanism that would explain the evolution, which he called natural selection.

Once again, that is a field disputable. There are much mechanisms to explain, in a partial manner, the evolution of species, such as genetic drift, horizontal transfer of genes and the natural selection itself. As you see, what still is disputable between scientists is how much weight attribute to mechanisms underlining the evolution of species and not whether or not they evolve. The idea that species evolve is intuitive and, until now, has been supported for overwhelming evidences. But the evolution’s idea, as said before, is older than evidences for it. Some kind of clairvoyant? Prophetic statement? Of course not! This is what we call verisimilitude. To understand better, suppose that you wish offer an explanation (conjectural) to a given phenomenon. The question would be some like that “If my explanation is correct, what would I expect to find as an experimental result?” Then, you begins to accumulate experimental evidences and observe if they fit into your conjectural model.  Accumulating evidences that support your explanation, you raise the probabilities of it is correct and decrease uncertainty related to it. Now, we can talk about conditional probability or function of verisimilitude with a bit more of confidence.

A conditional probability works to investigate the probability “P” of the explanation “A” is correct given that “B” is true, where B is an empirical evidence. The logic syntax would be: P (A | B), and this sounds too intuitive. Original explanatory models tend to be intuitive, since they are easier comprehensible by mind, this not imply in his correction (Cf. Propensão ao erro). Thus, the idea of evolution is intuitive and was proposed to explain why there are so many diversity of species on Earth. If that idea was true, we should find some indications for it. Fossil registers distributed on the geological eras, homology between organs in different species and great conserved regions in DNA suggesting  ancestrality are some examples of evidences that support the idea of species evolving trough the time. These evidences assume the place of “B” in our conditional probability syntax. How much more empirical evidences, higher the probabilities of our conjecture “A” is correct.

Therefore, the theory of evolution is a function of verisimilitude or what we call conditional probability. Summarily, this means that given some conditions (i.e., the observed evidences) we have a major or minor probability that our proposition is correct. Of course, as all probability, there’s some uncertainty attributed (Cf. The uncertainty value). We know, however, that some probabilities are so high that they are enough to discard the concurrent idea. That is the case of evolution’s probabilities are correct. Given the evidences that support the idea, the probability of the species evolve trough the time is higher. You still can not are satisfied with idea of conditional probability or verisimilitude. My suggestion is: keep in mind the contingent nature of the scientific knowledge; science do not generates final or immutable answers, but still is the better form to access reality.


Darwin, C.R. (1859) On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. Lodon: John Murray. [1st edition].
Darwin, C.R. (1871) The descent of man, and selection in relation to sex. Lodon: John Murray. Vol. 1.
Meyer, A. (2005) On the Importance of Being Ernst Mayr. PLoS Biol 3(5): e152. doi:10.1371/journal.pbio.0030152
Kimura, M (1968) Evolutionary rate at the molecular level. Nature 217 (5129): 624–626. doi:10.1038/217624a0

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This work by Alison Felipe Alencar Chaves is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.



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