[Pim's response]
Indeed and similarly we can observe how species appear in the fossil
record starting with simple single cellular to multi-cellular and so
onwards. Thus we can observe the evolution of species over time. This is
what is meant by the fact of evolution.
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I know that the notion of "evolution as fact" or "the fact of evolution"
has been discussed many times before, but I think the terms are being
used sloppily enough that they need to be sorted out. The comparison
with gravitation has been made by others, so I will use it to explain
my viewpoint.
There is a vast difference between (i) observational data and (ii)
theoretical explanation. The word FACT is not a helpful one, in my
view, because it implies certainty. Contemporary philosophy of science
tells us that even the data we observe depend to some extent on the
presuppositions and prior assumptions of the observer. And no scientific
theory can be proven in the sense of a mathematical proof.
What Pim describes above is the observational data that "species appear in the
fossil record starting with simple single cellular to multi-cellular and so
onwards". Even this observation depends on the acceptance of various
assumptions about dating the fossil finds. But it seems a valid observation,
given a certain set of assumptions.
In the case of celestial mechanics, the corresponding observational data (much
more quantitative, to be sure) are the regular orbits of planets about the sun,
whose positions as a function of time can be measured. These measurements also
depend on a set of initial assumptions.
A theoretical explanation is then sought for the pattern of observed events (or
data). In the case of the fossil record, one possible theory is the theory of
common ancestry (TCA). I realize that "evolution" as commonly understood
involves more than just this, but TCA is one central component of what is
called "evolution". This theory generates certain predictions, or at least
expectations, for example, the prediction that we should find transitional
sequences between species in the fossil record. The validity of the theory
is then judged on the basis of many criteria, *one* of which is how well its
predictions are borne out by further observation. One should not call any
theoretical explanation a FACT, for reasons I mentioned above. Certainly
many people find compelling evidence to accept TCA, but it is not a FACT.
In the case of celestial mechanics, one theory (due to Newton) is that the
planets exert forces on one another in accordance with the following
expression:
G*M1*M2
F = --------
2
r
in terms of the masses M1 and M2 and the distance r. G is the proportionality
constant. This force makes the mathematical prediction of elliptical
orbits with the sun at one focus, and provides a very accurate fit to the
observed planetary orbits. Nevertheless, this theory has limitations which
are well-known, and is not regarded as the final word, even in planetary
motion. I would say that within certain limits this theoretical explanation
is strongly confirmed by the observational data, but would still resist calling
it a FACT as explained above.
It seems to me that the use of the phrase "the FACT of evolution" is misleading
and is based on a redefinition of the word "evolution" from the way it is
commonly used--as a description of a *theoretical framework* for explaining
observed patterns in the fossil record, etc. I do not wish to discuss the
motives of those who employ this redefinition of the term, but at the very least
I would say it is not conducive to clear communication, as the recent exchanges
have shown.
For my benefit, please let me know if what I have written seems correct. If
not, I would like to know where I have gone wrong.
Thank you,
Stan Zygmunt
Dept. of Physics and Astronomy
Valparaiso University
Valparaiso, IN 46383