One of the characteristics of post-modernism is the overlap between facts and theories. In modern science theories were based on facts, theories explained facts, and theories connected facts together. But post-modernism blurs the distinction between facts and theories. For example:
In science, a “fact” typically refers to an observation, measurement, or other form of evidence that can be expected to occur the same way under similar circumstances. However, scientists also use the term “fact” to refer to a scientific explanation that has been tested and confirmed so many times that there is no longer a compelling reason to keep testing it or looking for additional examples. Because the evidence supporting it is so strong, scientists no longer question whether biological evolution has occurred and is continuing to occur. Instead, they investigate the mechanisms of evolution, how rapidly evolution can take place, and related questions. The National Academies – Evolution Resources [The National Academies is also known as the (U.S.) National Academy of Sciences.]
It is easily seen that the term “evolution” is used in (at least) two different senses. Under Definitions, the above website provides the following:
Evolution: Evolution consists of changes in the heritable traits of a population of organisms as successive generations replace one another. It is populations of organisms that evolve, not individual organisms.
That is the factual part. But there is another part, the theory part, which is obscured by not distinguishing fact from theory. For example, their entire website only mentions common descent once, and that in reference to additional resources:
With the publication in 1859 of On the Origin of Species by Means of Natural Selection, Charles Darwin established evolution by common descent as the dominant scientific explanation for nature’s diversity. The National Academies – Darwin’s Gift to Science and Religion
Note also the reification of nature (“nature’s diversity”) and evolution as a “gift” (as if Darwin brought it down from Mt. Science).
But in the context of Darwin’s The Origin of Species by Means of Natural Selection and the modern theories of evolution, “evolution is a fact” may tend to block a full view of the major theories and the hundreds of subtheories found in the study of evolution (Lewis, 1980). NCSE – Theory and the Fact of Evolution.
What does the theory part of evolution include? U. Kutschera and K.J. Niklas list the principal propositions of Darwin’s theory:
1. Supernatural acts of the Creator are incompatible with empirical facts of nature
2. All life evolved from one or few simple kinds of organisms
3. Species evolve from pre-existing varieties by means of natural selection
4. The birth of a species is gradual and of long duration
5. Higher taxa (genera, families etc.) evolve by the same mechanisms as those responsible for the origin of species
6. The greater the similarities among taxa, the more closely they are related evolutionarily and the shorter their divergence time from a last common ancestor
7. Extinction is primarily the result of interspecific competition
8. The geological record is incomplete: the absence of transitional forms between species and higher taxa is due to gaps in our current knowledge
Naturwissenschaften (2004) 91:255–276
All of these propositions are theoretical. The modern synthesis version of evolution adds the genetics of populations to this (Systematics and the origin of species: An introductiom – Hey, Fitch, and Ayala).
So the “fact of evolution” is quite different from the propositions claimed about evolution. The fact – “changes in the heritable traits of a population of organisms as successive generations replace one another” – is better described as variation. It consists of differences observed between the generations. These are the variations that naturally occur.
The term “evolution” implies progress- etymologically, it means an unrolling. Evolution was applied by Herbert Spencer first to society. “Social progress is in fact viewed as a natural evolution”. He was “the first to work out a comprehensive philosophical system … on the basis of the principle of Evolution.” (Herbert Spencer and the Doctrine of Evolution)
But progress is not observed between the generations. What is observed is variation. It is misleading to use the word “evolution” to describe the observation of variation.