Critias said:When did science come out and say common descent is fact, not theory?
I didn't say common descent. I said evolution. Common descent is a sub-theory of the theory of evolution.
Evolution is a fact. We know this from observation.
The theory of evolution is a theory which attempts to explain how evolution happens. It is a comprehensive set of ideas which are explanatory and predictive of observed evidence.
The theory of evolution includes a number of sub-theories. For example, one of its sub-theories is that natural selection is a significant cause of evolutionary changes.
Note that this theory is not about the evolutionary changes themselves. We can see them and know that they occur. It is about the mechanism that regulates these changes and causes species to change. This is what is meant by the theory being explanatory.
However, we need more than a hypothetical explanation of how evolution happens. Scientists want to know whether natural selection really happens and if it really produces evolutionary change. To answer that question they make predictions along the line of:
Assuming that natural selection really does change species, then in case A we should observe X. And they set up an experiment in which to test whether X is really observed in case A.
This is not the easiest thing to do, but there have been enough such experiments done in both lab conditions and in the field to verify that natural selection is not just a hypothetical mechanism (as it was for Darwin), but a real observable process.
So much for mechanism. The other part of the study of evolution is to determine as far as possible the actual history of evolution. This is even more difficult to test for than natural selection. But one can still use the same process.
We know evolution happens in the present.
We have every reason to assume that it also happened in the past.
We know speciation happens and that the species of the present had ancestors in the past.
We have every reason to assume that recent ancestors had more distant ancestors and that they had more distant ancestors.
We can therefore infer that when all ancestors are traced back through more and more remote ancestors we will find they all converge on one common ancestor.
This is a logical inference and as a logical inference it is entirely hypothetical, not fact.
However, the purpose of a hypothesis is to generate predictions of observations which must exist if the hypothesis is true. This whole train of thought gives us many predictions of things that must be fact if the hypothesis is true.
And research has shown that many of these predictions are fact. e.g. the close genetic resemblance of humans to other apes, especially the chimpanzees; the possibility that some dinosaurs had feathers; the successful prediction that we would eventually see the fossil record extended into the Pre-Cambrian (in fact we now have fossils 7 times older than the earliest Cambrian fossils) and the successful predictions of fossils that bridged the higher taxa such as fish/amphibian and reptile/mammal. IOW what we expect to see in nature if all life has a common ancestor is what we actually DO SEE in nature. This is even more true of the more recently discovered genetic evidence. From the study of DNA sequences in a variety of species, it is more certain than ever that all life shares commonalities that transcend species. Furthermore, the pattern in which these commonalities are shared are not the same as the patterns found in manufactured objects, but patterns which are found in genealogies. IOW it appears that the mechanism of sharing common DNA is reproduction, not design.
So at this point, common ancestry is no longer just a logical inference. It is a concept well-supported by the evidence of nature. In fact some of the evidence in nature (e.g ERVs) simply has no other possible reason for existing than common ancestry.
The fact of evolution makes common ancestry logical. The accumulated evidence which supports common ancestry or which can be explained only by common ancestry means this is not just logical. It is the testimony of created nature. And created nature is given to us by God.
So if you are truly interested in listening to the Word of God, it is foolish not to consider the high probabilty of common ancestry.
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