Creationist Objections To Evolution - Scientific Status - Unfalsifiability

Unfalsifiability

A statement is considered falsifiable if there is an observation or a test that could be made that would demonstrate that the statement is false. Statements that are not falsifiable cannot be examined by scientific investigation since they permit no tests that evaluate their accuracy. Creationists such as Henry M. Morris have claimed that evolution is unfalsifiable. They claim that any observation can be fitted into the evolutionary framework, and that therefore it is impossible to demonstrate that evolution is wrong. As such, they claim that evolution is non-scientific.

However, evolution is considered falsifiable by scientists because it can make predictions that, were they contradicted by the evidence, would falsify evolution. Several kinds of evidence have been proposed that could falsify evolution, such as the fossil record showing no change over time, confirmation that mutations are prevented from accumulating, or observations showing organisms being created supernaturally or spontaneously. Many of Darwin's ideas and assertions of fact have been falsified as evolutionary science has developed and has continued to confirm his central concepts. Despite this, creationism consists largely of unsubstantiated claims that evolution has been falsified. In contrast, creationist explanations involving the direct intervention of the supernatural in the physical world are not falsifiable, because any result of an experiment or investigation could be the unpredictable action of an omnipotent deity.

In 1976, philosopher Karl Popper said that "Darwinism is not a testable scientific theory but a metaphysical research programme". However, Popper later recanted and offered a more nuanced view of its status:

However, Darwin's own most important contribution to the theory of evolution, his theory of natural selection, is difficult to test. There are some tests, even some experimental tests; and in some cases, such as the famous phenomenon known as 'industrial melanism', we can observe natural selection happening under our very eyes, as it were. Nevertheless, really severe tests of the theory of natural selection are hard to come by, much more so than tests of otherwise comparable theories in physics or chemistry.

The most direct evidence that evolutionary theory is falsifiable may be the original words of Charles Darwin who, in chapter 6 of On the Origin of Species wrote: "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."

In response to the unfalsifiability criticism of evolutionary theory, numerous examples of potential ways to falsify evolution have been proposed. J.B.S. Haldane, when asked what hypothetical evidence could disprove evolution, replied "fossil rabbits in the Precambrian era". Numerous other potential ways to falsify evolution have also been proposed. For example, the fact that humans have one fewer pair of chromosomes than the great apes offered a testable hypothesis involving the fusion or splitting of chromosomes from a common ancestor. The fusion hypothesis was confirmed in 2005 by discovery that human chromosome 2 is homologous with a fusion of two chromosomes that remain separate in other primates. Extra, inactive telomeres and centromeres remain on human chromosome 2 as a result of the fusion. The assertion of common descent could also have been disproven with the invention of DNA analysis. If true, human DNA should be far more similar to chimpanzees and other great apes, than to other mammals. If not, then common descent is falsified. DNA analysis has shown that humans and chimpanzees share a large percentage of their DNA (between 95% to 99.4% depending on the measure). Also, the evolution of chimpanzees and humans from a common ancestor predicts a (geologically) recent common ancestor. Numerous transitional fossils have since been found. Hence, human evolution has passed several falsifiable tests.

A related claim is that natural selection is tautological. Specifically, it is often argued that the phrase "survival of the fittest" is a tautology, in that fitness is defined as ability to survive and reproduce. However, this phrase, first used by Herbert Spencer in 1864, is rarely used by biologists. Additionally, fitness is more accurately defined as the state of possessing traits that make survival more likely; this definition, unlike simple "survivability", avoids being trivially true.

Similarly, it is argued that evolutionary theory is circular reasoning, in that evidence is interpreted as supporting evolution, but evolution is required to interpret the evidence. An example of this is the claim that geological strata are dated through the fossils they hold, but that fossils are in turn dated by the strata they are in. However, in most cases strata are not dated by their fossils, but by their position relative to other strata and by radiometric dating, and most strata were dated before the theory of evolution was formulated.

In his book, Abusing Science: The Case Against Creationism, philosopher of science Philip Kitcher specifically addresses the "falsifiability" question by taking into account notable philosophical critiques of Popper by Carl Gustav Hempel and Willard Van Orman Quine that reject his definition of theory as a set of falsifiable statements. As Kitcher points out, if one took a strictly Popperian view of "theory," observations of Uranus when first discovered in 1781 would have "falsified" Newton's celestial mechanics. Rather, people suggested that another planet influenced Uranus' orbit – and this prediction was indeed eventually confirmed. Kitcher agrees with Popper that "there is surely something right in the idea that a science can succeed only if it can fail." But he insists that we view scientific theories as consisting of an "elaborate collection of statements," some of which are not falsifiable, and others – what he calls "auxiliary hypotheses," which are.

According to Kitcher, good scientific theories must have three features – unity, fecundity, and independent testability of auxiliary hypotheses:

Unity

"A science should be unified .... Good theories consist of just one problem-solving strategy, or a small family of problem-solving strategies, that can be applied to a wide range of problems" (1982: 47).

Fecundity

A great scientific theory, like Newton's, opens up new areas of research... Because a theory presents a new way of looking at the world, it can lead us to ask new questions, and so to embark on new and fruitful lines of inquiry... Typically, a flourishing science is incomplete. At any time, it raises more questions than it can currently answer. But incompleteness is no vice. On the contrary, incompleteness is the mother of fecundity... A good theory should be productive; it should raise new questions and presume that those questions can be answered without giving up its problem-solving strategies (1982: 47–48).

Auxiliary hypotheses that are independently testable

"An auxiliary hypothesis ought to be testable independently of the particular problem it is introduced to solve, independently of the theory it is designed to save" (1982: 46) (e.g. the evidence for the existence of Neptune is independent of the anomalies in Uranus's orbit).

Like other definitions of theories, including Popper's, Kitcher makes it clear that a good theory includes statements that have (in his terms) "observational consequences." But, like the observation of irregularities in Uranus's orbit, falsification is only one possible consequence of an observation. The production of new hypotheses is another possible – and equally important – observational consequence. Kitcher's account of a good theory is based not only on his understanding of how physical sciences work. He is also taking into account the way the life sciences work.

From Kitcher's point of view, Darwinian theory not only meets the three conditions for a good scientific theory; it is without question an extraordinarily successful theory:

The heart of Darwinian evolutionary theory is a family of problem-solving strategies, related by their common employment of a particular style of historical narrative. A Darwinian history is a piece of reasoning of the following general form. The first step consists in a description of an ancestral population of organisms. The reasoning proceeds by tracing the modification of the population through subsequent generations, showing how characteristics were selected, inherited, and became prevalent. Reasoning like this can be used to answer a host of biological questions.
The same kind of story can be told again and again to answer all sorts of questions about all sorts of living things. Evolutionary theory is unified because so many diverse questions ... can be addressed by advancing Darwinian histories. Moreover, these narratives constantly make claims that are subject to independent check.
Darwin not only provided a scheme for unifying the diversity of life. He also gave a structure to our ignorance. After Darwin, it was important to resolve general issues about the presuppositions of Darwinian histories. The way in which biology should proceed had been made admirably plain, and it was clear that biologists had to tackle questions for which they had, as yet, no answers.