One of the main time-honored (and very reasonable) criteria of a scientific theory is that it be falsifiable. A theory is falsifiable if it admits of a way that it could possibly be proven wrong.
For example, in Newtonian physics, an object thrown up in the air will follow a parabolic path. If we actually go outside (on the moon, say, so that air resistance is not a factor), throw something up in the air, use a computer and a camcorder to record its flight path, and find that its motion was not parabolic, we have thus disproven Newtonian mechanics.
Falsifiability is an absolutely essential component of worthwhile scientific theories - for if a theory could never, under any practical circumstances, be proven false, it is almost certainly too vaguely worded, too free from potential criticism, to make valid predictions.
Carl Sagan uses the famous example of “there is a Dragon in my garage.” His friend then replies, “oh, I should love to see the dragon!” whereupon he responds, “ah, but this dragon is invisible.” His friend says “well, I can feel the heat of his fire”, but Carl says that the dragon’s fire is exactly room temperature. One can continue with this line of attack and arrive at the conclusion that there is no way, empirically, to disprove this hypothetical dragon. Yet clearly we don’t believe it to exist. The necessity of falsifiability is what allows us to dispose of the dragon theory swiftly.
Indeed, it is the concept of falsifiability that so neatly disposes of the “theory” of Intelligent Design. One can never empirically disprove that we were created by some sort of God. Even if we recreate life in the lab, or go back in time and witness the birth of the first amino acids, that can be explained as happening via the will of God.
But Evolution - biology’s most sacred theory, and one of the most practically useful theories ever to come from science, seems in some sense unfalsifiable. Evolution cannot predict how an organism will evolve, because the principles of natural selection are massively too complex to allow such predictions. Thus evolution is limited mostly to explanations of how things came to pass. So if I wished to disprove evolution, I could go the same route as the creationists, and claim that certain organisms, or certain organs, could never have evolved slowly. The classic example is the eye - the eye is so perfect and useful that it could not have happened “by chance” - nor would an eye without some of its components be useful in the least, and thus could not have evolved, but rather had to appear fully formed.
This particular example, and indeed all the particular examples cited by creationists, are laughably ridiculous. The eye is far from perfect - the vitreous and aqueous humors, the jelly-like substances in the eye, are necessary for the eye to form correctly during gestation and infancy, but in later years have a propensity to harden that is very harmful to the eye. It has long been known that, when in adulthood, saline solution in the eye is entirely preferable to the evolved substances.
Further, the idea that the eye would be useless in anything but a fully formed state is clearly false. The eye almost certainly began as a single light-sensitive cell. It is true that this would confer an almost negligible survival advantage, but it confers one nonetheless. An organism that had awareness of light could detect a quick change in light levels, and flee, assuming a predator or a dangerous environment. Over a few hundred years this wouldn’t amount to much, but over thousands or millions of years, the marginal survival advantage would result in many more organisms with the light-sensitivity, and with many more light-sensitive cells than before.
Nonetheless, even if the eye is a poor attempt to discredit evolution, what of hypothetical examples that pack a greater punch? Consider the factor of the “missing link”. Although the human’s closest living ancestor is the chimpanzee, we did not evolve from chimps per se - rather, both we and chimps evolved from a common ancestor. However, there is no record of this ancestor, either living or dead, despite significant efforts to find it. Now, many of you are thinking, “surely this isn’t an objection to evolution. Just because we haven’t found it yet doesn’t mean that we never will.” This is exactly correct, of course. But the fact that one can respond in that manner to every “gap” in the evolutionary record seems to indicate a lack of falsifiability in that sense.
Consider further another “eye” example that also packs a greater punch. We can see how the eye could have evolved from a single light-sensitive cell, and did not need to be created fully-formed. Well, let’s forget about that, and imagine an organism, or an organ, whose evolutionary lineage we can’t explain. If we found such a thing, would it be proof that evolution was wrong? Certainly not, for the same reason as regards the missing link: just because we can’t generate an explanation for it now doesn’t mean that there isn’t one. There are so many strange factors that occur in nature that it would be ridiculous to imagine that we know all of them, or can fully understand their mechanisms. An evolutionary lineage we can’t explain now will almost certainly be explainable at some point in the future when we have a greater understanding of the factors that underlie its organismal history.
This analysis is also correct - there is nothing logically inconsistent about it. But it seems to further render evolution as an unfalsifiable theory.
So is it true that evolution is unfalsifiable? And if so, what does that mean about it as a theory?