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29+ Evidences for Macroevolution
Copyright © 1999-2003 by Douglas Theobald,
What is meant
by scientific evidences and scientific proof? In truth, science can never
establish "truth" or "fact" in the sense that a scientific statement can be made
that is formally beyond question. All scientific statements and concepts are
open to reevaluation as new data is acquired and novel technologies emerge.
"Proof", then, is solely the realm of logic and mathematics. That said, we often
hear "proof" mentioned in a scientific context, and there is a sense in which it
denotes "strongly supported by scientific means". Even though one may hear
"proof" used like this, it is a careless and inaccurate handling of the term.
Consequently, except in reference to mathematics, this is the last time you will
read the terms "proof" or "prove" in this article.
Common Sense is Not Science
Though science formally cannot establish absolute truth, it can provide
overwhelming evidence in favor of certain ideas. Often these ideas are quite
unobvious, and usually they clash with common sense. Common sense tells us that
the earth is flat, that the Sun truly rises and sets, that the surface of the
Earth is not spinning at over 1000 miles per hour, that bowling balls fall
faster than marbles, that particles don't curve around corners like waves around
a floating dock, that the continents don't move, and that objects
heavier-than-air can't have sustained flight unless they can flap wings.
However, science has been used to demonstrate that all these common sense ideas
Science Provides Evidence for the Unobservable
The primary function of science is to demonstrate the existence of phenomena
that cannot be observed directly. Science is not needed to show us things we can
see with our own eyes. Direct observation is not only unnecessary in science;
direct observation is in fact usually impossible for things that really matter.
For example, the most important discoveries of science can only be
inferred via indirect observation, including such things as atoms,
electrons, viruses, bacteria, germs, radiowaves, X-rays, ultraviolet light,
energy, entropy, enthalpy, solar fusion, genes, protein enzymes, and the DNA
double-helix. The round earth was not observed directly by humans until 1961,
yet this counterintuitive concept had been considered a scientific fact for over
2000 years. The Copernican hypothesis that the earth orbits the sun has been
acknowledged virtually ever since the time of Galileo, though no one has ever
observed the process to this day and in spite of the fact that direct
observation indicates the very opposite. All of these "invisible" inferences
were elucidated using the scientific method. When the term "evidence" is used in
this article, it is used strictly in the context of this scientific method.
The Scientific Method: More than Mere Experimentation
What is the scientific method? This is a complex and contentious question,
and the field of inquiry known as the philosophy of science is committed to
illuminating the nature of the scientific method. Probably the most influential
philosopher of science of the 20th century was Sir Karl Popper. Other
notables are Thomas Kuhn, Imre Lakatos, Paul Feyerabend, Paul Kitcher, A. F.
Chalmers, Wesley Salmon and Bas C. van Fraassen. This is not the place to delve
into an explication of the various philosophies represented by these scholars;
for more information I refer you to their works and to the discussion presented
by John Wilkins in his Evolution and Philosophy
FAQ. I personally take an experimentalist and comparative Bayesian view of
the scientific method (Salmon
1996), and this will come through in how I present the evidence for common
Now, to answer the question "What is the scientific method?" - very simply
(and somewhat naively), the scientific method is a program for research which
comprises four main steps. In practice these steps follow more of a logical
order than a chronological one:
- Make observations.
- Form a testable, unifying hypothesis to explain these observations.
- Deduce predictions from the hypothesis.
- Search for confirmations of the predictions;
if the predictions are
contradicted by empirical observation, go back to step (2).
Because scientists are constantly making new observations and testing via
those observations, the four "steps" are actually practiced concurrently. New
observations, although they were not predicted, should be explicable
retrospectively by the hypothesis. New information, especially details of some
process previously not understood, can impose new limits on the original
hypothesis. Therefore, new information, in combination with an old hypothesis,
frequently leads to novel predictions that can be tested further.
Examination of the scientific method reveals that science involves much more
than naive empiricism. Research that only involves simple observation,
repetition, and measurement is not sufficient to count as science. These three
techniques are merely part of the process of making observations (#1 in the
steps outlined above). Astrologers, wiccans, alchemists, and shamans all
observe, repeat, and measure—but they do not practice science. Clearly, what
distinguishes science is the way in which observations are interpreted, tested,
The Testable Hypothesis
The defining characteristic of science is the concept of the testable
hypothesis. A testable hypothesis must make predictions that can be validated by
independent observers. By "testable", we mean the predictions must include
examples of what should be observed if the hypothesis is true and of what
should not be observed if the hypothesis is true. A hypothesis that can
explain all possible observations and data is not testable nor is it scientific.
A good scientific hypothesis must rule out some conceivable possibilities, at
least in principle. Furthermore, a scientific explanation must make risky
predictions—the predictions should be necessary if the theory is correct, and
few other theories should make the same necessary predictions. These scientific
requirements are the essence of Popperian falsifiability and corroboration.
For instance, the solipsistic hypothesis that the entire universe is actually
an elaborate figment of your imagination is not a scientific hypothesis.
Solipsism makes no specific or risky predictions, it simply predicts that things
will be "as they are". No possible observations could conflict with solipsism,
since all observations always may be explained away as simply another detailed
creation of your imagination. Many other extreme examples can be thought of,
such as the hypothesis that the universe suddenly came into existence in
toto five minutes ago, with even our memories of "earlier" events intact. In
general, creationist and "intelligent design" conjectures fail scientifically
for these same reasons, since both can easily explain all possible biological
observations, and since both make no risky, specific predictions.
In contrast, Newton's scientific theory of universal gravitation predicts
that the force between two masses should be inversely proportional to the square
of the distance between them (otherwise known as the "inverse square law"). In
principle, we could take measurements which indicated that the force is actually
inversely proportional to the cube of the distance. Such an observation would be
inconsistent with the predictions of Newton's universal theory of gravitation,
and thus this theory is falsifiable. Anti-evolutionists, such as the
"scientific" creationists, are especially fond of Karl Popper and his
falsifiability criterion, and they are well known for claiming that evolutionary
theory is unscientific because it cannot be falsified. In this article, these
accusations are met head on. Each of the evidences given for common descent
contains a section providing examples of potential falsifications, i.e. examples
of observations that are predicted not to be observed if the theory is
Degrees of Testability: Hypotheses, Theories, Facts
"Testability" is not an either-or concept; some hypotheses are more testable
than others. Contrary to some anti-evolutionist claims, not all hypotheses are
equally valid scientific "interpretations" of the evidence. Some hypotheses are
more successful in terms of the scientific method. Based on the scientific
method, a hypothesis that simply and elegantly explains the observed facts, that
predicts many previously unobserved phenomena, and that withstands many
potential falsifications is considered a valid and useful hypothesis. From a
Bayesian perspective and according to Popper's corroboration measure, the best
hypothesis available is the one that explains the most facts with the fewest
assumptions, the one that makes the most confirmed predictions, and the one that
is most open to testing and falsification.
In scientific practice, a superior and well-supported hypothesis will be
regarded as a theory. A theory that has withstood the test of time and the
collection of new data is about as close as we can get to a scientific fact. An
example is the aforementioned notion of a heliocentric solar system. At one time
it was a mere hypothesis. Although it is still formally just a well-supported
theory, validated by many independent lines of evidence, it is now widely
regarded as scientific "fact". Nobody has ever directly observed an electron,
stellar fusion, radiowaves, entropy, or the earth circling the Sun, yet these
are all scientific facts. As Stephen J. Gould has said, a scientific fact is not
"absolute certainty", but simply a theory that has been "confirmed to such a
degree that it would be perverse to withhold provisional consent".
Testing Involves a Totality of Evidence and Statistics
The validity of a hypothesis does not stand or fall based on just a few
confirmations or contradictions, but on the totality of the evidence. Often,
data that initially may seem to be inconsistent with a theory will in fact lead
to new important predictions. The history of Newtonian physics gives a clear
example. The abnormal movement of Uranus was initially considered a potential
falsification of Newton's new theory. However, by claiming the existence of an
unseen planet, the anomaly was explained within Newton's paradigm. In general,
an explanation for anomalous behavior should be considered ad hoc unless
it is independently verifiable. Positing a new, unseen planet might be
considered hedging if there were no independent way to detect if a new planet
actually existed. Nevertheless, when technology had advanced enough to reliably
test the new prediction, the unseen planet was found to be Neptune.
The lesson to be learned is that alternate explanations for "anomalies"
should be treated like any other hypotheses: they should be weighed, tested, and
either ruled out or confirmed. But a hypothesis should not be considered
falsified until thorough testing has produced multiple lines of positive
evidence indicating that the hypothesis is truly inconsistent with the empirical
A crucial related point is that modern scientific theories are probabalistic.
This means that all testing of scientific predictions is carried out in a statistical framework.
Probability and statistics pervade modern scientific theories, including
thermodynamics (statistical mechanics), geology, quantum mechanics, genetics,
and medicine. The mathematics of probability is a discipline that many people
find, shall we say, distasteful. However, a working knowledge of statistics is
absolutely essential for judging the fit between observed data and the
predictions of any theory.
Chalmers, A. F. (1982) What is this thing called
Science? Queensland, Australia, University of Queensland Press.
Stephen J. Gould (1981) "Evolution as Fact and Theory."
Discover. May issue.
Kuhn, T. (1970) The Structure of Scientific
Lakatos, I. (1974) "Falsification and the Methodology
of Scientific Research Progammes." Criticism and the Growth of Knowledge.
I. Lakatos and A. Musgrave. Cambridge, Cambridge University Press: 91-196.
Mayo, D. (1996) Error and the Growth of Experimental
Knowledge. Chicago, University of Chicago Press.
Popper, K. R. (1968) The Logic of Scientific
Discovery. London, Hutchinson.
Salmon, W. (1990) "Rationality and Objectivity in
Science, or Tom Kuhn meets Tom Bayes." Scientific Theories. C. W. Savage.
Minneapolis, University of Minnesota Press. 14.
von Fraassen, B. C. (1980) The Scientific
Image. Oxford, Clarendon Press.