An interesting discussion occurred in the comments to my recent post on home schooling textbooks. As this question frequently occurs in discussions of evolution, I think it worthy of its own post. Besides, I love this sort of thing.
Commenter Human Ape said this:
Evolution is a basic scientific fact.
That led to the larger discussion of evolutionary theory and its status in science
Stan Gibilisco wrote this:
I accept that according to the evidence, the scientific method leads us to conclude that evolution is by far the most reasonable theory concerning life on this planet, and it explains better than any other theory how we humans got here.
I argue that such terms as truth and fact are appropriate to the courtroom but not the laboratory. In the former venue, I want to know if a witness is telling the truth and if the defendant in fact committed the crime. Science, by contrast, is concerned with data, hypothesis, experiment, and theory, all of which are in principle subject to revision. It's not that scientists are uninterested in the truth; it's that a good theory, based on data, confirmed by experiment and research, and generating further research programs, is as close to the truth as any science can get.
I also supported Stan in his statement about evolution, and in particular about speciation (the idea that new species emerge out of older ones in the history of living organisms).
My SDP colleague, Miranda, wrote this reply to me in the most recent comment:
You suggest that there is as much proof for speciation as anything in biology. I disagree. Some biological theories are easy to prove or disprove. We can, for instance, theorize that children tend to grow taller than their parents. Then we can measure parents and children over the course of time to arrive at a solid answer. Theories that can be tested with measurements and direct observation are, I think, easier to prove than theories about man's relation to slime molds.
I return here to the distinction between the common sense etiology (explanation by causation) appropriate to the courtroom and scientific etiology. In the context of the former, Miranda is surely right. It's relatively easy to determine whether children do or do not tend to grow taller than their parents.
But gathering such information would be only the first step in science. The scientist wants to develop hypotheses concerning the laws or causes that operate in this case, test the hypotheses, and integrate them into general theory.
From the viewpoint of science, I would argue that it is precisely the opposite of what Miranda says. The theory of evolution by common descent, including the concept of speciation, is much better established than any science concerning the heritability of stature.
It is generally assumed that the height of individuals is influenced both by heritable factors like genes and by environmental factors like nutrition. It's notoriously difficult to tease these influences apart. Suppose someone advanced this thesis: the influence of biologically inherited factors on height is negligible; rather, height is, say, 98% a function of environmental factors. Such a thesis would look very unlikely, but it is not out of the realm of possibility. If confirmed, it would please sociologists but it would require no great revision in genetics or other fields of biology, nor would it require any scientifically unusual assumptions.
Now suppose someone advances this thesis: speciation never happens. This would require a rejection or at least a traumatic reinterpretation of the basic history and classification of the species in modern biology. Worse still, one would have to assume either that every existing species has been present since the beginning of life on earth or that new species spontaneously come into being out of nothing. In either case, morphological similarities would have to be interpreted as very odd coincidences or perhaps a lazy imagination on the part of the Creator. In the former case, since many species are highly dependent on specialized ecological niches, one would have to revise the entire science of geology as well.
I reassert my statement that speciation in particular (and evolution from a common ancestor in general) is about as well established as anything in modern biology. However, in so asserting it, I note that Miranda and Stan and I are in agreement regarding the political question. Darwinian evolution ought to be part of the curriculum of a public high school. Home schoolers have to meet certain standards, and perhaps those standards should include an understanding of what evolutionary theory says. But parents should never be required to tell their children that evolution is true.
The distinction between theory and fact has nothing to do with greater certainty on the one side than the other. It is all about different approaches to the matter at hand in different contexts.
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