A couple of weeks ago a very good post on abduction appeared on Mormon Organon (view it here). In that post, Mr. Peck correctly argues that abduction, or inference to the best explanation as it is sometimes called, refers to a sort of logical competition between theories. A theory that explains a body of evidence better than its rival theory is more reasonable to accept. If we apply this concept to theories on the origins and complexities of species, evolution is the clear winner, although probably more by default than anything else. But this explains why evolution is so widely accepted. It is simply the best scientific theory available for explaining the origins and complexities of life.

Mr. Peck also effectively pointed out that most theories are created through accumulating observation and empirical facts. The process of collecting empirical facts and creating a suitable theory that explains those facts is sometimes referred to as an inductive generalization. Put differently, an inductive generalization involves moving from many observations to a single, explanatory theory. Many great theories like evolution have been created via inductive generalizations. Creating scientific theories through inductive generalizations is not a theoretical faux pas or scientific weakness; it is just one aspect of how science progresses.  

So far we have only considered the logic of theory discovery. As stated above, scientific abduction plays a role in determining which theories gain prominence. It also plays a role in determining which theory will be singled out for confirmatory investigation, however, the process of confirming a theory through testing is different from abduction.

The most common approach to confirming scientific theories is the hypothetico-deductive (H-D) model of science. In short, the H-D model of science involves deducing observational hypotheses from a theory and testing those hypotheses in a controlled setting. If the results are consistent with the theory’s expectations, then the theory is tentatively confirmed. If the results are not consistent with the theory’s expectations, then the theory is tentatively disconfirmed.

Not all H-D tests of hypotheses are created equal. Influential philosopher of science Karl Popper pointed out that an ideal test of a hypothesis is one that is falsifiable and addresses, as much as possible, the core tenets of the theory. Popper called it making a risky prediction.

Theories that repeatedly survive falsifiable tests and risky predictions gain “certainty” status; we become so certain of their truthfulness that we start calling them laws instead of theories. Theories that have repeatedly survived falsifiable, risky predictions include Relativity, gravity, and the Germ Theory of Disease, to name a few.

Now, because of lengthy time requirements needed for testing falsifiable macroevolutionary hypotheses that make risky predictions a’la the H-D model of science, macroevolution has not risen to the same level of certainty we typically associate with Relativity and gravity. Relativity and gravity have repeatedly undergone crucial testing. In most cases, the results of these tests have been confirmatory (i.e., 1919 Sir Arthur Eddington solar eclipse expedition, atomic clocks in airplanes, and every time you drop your pen it falls, as predicted.)

I don’t have a problem with people saying that they personally accept the certainty of the theory of common descent. Evolution’s pre-eminence in the game of scientific abduction makes this statement legitimate. I do have a problem with people claiming that macroevolution and common descent have been proven beyond a reasonable doubt. IMO, the scarcity of confirmed falsifiable and crucial tests of macroevolutionary processes does not warrant such claims.

Sources: (Philosophy of Science: A to Z by Stathis Psillos; Philosophy of Science: The Central Issues by Curd & Cover; Philosophy of Science: A Short Introduction by Samir Okasha.)