Irreducible Complexity and Darwin's Theory of Evolution

Introduction: Irreducible Complexity and Evolutionary Theory

The construct of irreducible complexity is a pivotal aspect of genetic theory and of Darwinian theory. Irreducible complexity is a nexus of the older science of biology from which Darwin built his theory and modern genetic engineering. Darwin's words for irreducible complexity, most commonly associated with his argument about the construction of the eye, were "Organs of extreme perfection and complication." Darwin further elaborated on this observation:

"Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory" (Darwin 1859).

Examples of irreducible complexity on the biological organ level include the heart, the eye, and the ear—though they were not recognized as irreducible structures in Darwin's lifetime—and there are, in fact, "tens of thousands of irreducibly complex systems on the cellular level" (Abbey et al. 2011). The construct of irreducible complexity may be seen as a foundation of Darwin's theory of evolution, as Darwin observed that "complex forms evolve from non-complex forms over time...based on natural selection, which acts to accumulate and transform minor advantageous genetic mutations" (Abbey et al. 2005).

It is important to link the two disciplines, since to argue for or against evidence of Darwin's theory without framing it in scientific progress is akin to claiming that Don Quixote cannot be the first modern novel because it is, after all, simply a written record of the ballads in the tradition of picaresque novels. Don Quixote was the novel of its time—indeed, the only anti-romantic novel of the era—in quite the same way that the theory of evolution was the explanation for inherited biological difference that related to environmental survival.

The Peppered Moth: A Living Example of Natural Selection

One of the simplest and most instructive examples of Darwin's theory of evolution can be accessed by referring to the study of peppered moths in English industrial cities. Peppered moths as a species present a variety of wing and body coloration patterns, which have apparently changed—or evolved—over time (Majerus 2004). In nineteenth-century England, people heated homes, factories, and common spaces with coal-burning furnaces, without any type of filter that would reduce environmental pollution (Majerus 2004).

As a result of this heavy pollution, the lichen that grew on the trees under normal conditions was killed, and where the tree bark had once been light in color, it became darkened by deposits of coal soot (Majerus 2004). Indeed, the exteriors of buildings were also turned dark by the coal soot deposits. Unfortunately for some of the peppered moths, light-colored wings stood out rather starkly on dark-colored surfaces, which served to attract hungry, savvy birds to easy meals (Majerus 2004). The birds did not as readily pick off moths that were naturally located on the darker end of the wing and body color spectrum (Majerus 2004).

As would be expected, more dark-colored peppered moths survived in higher numbers and—genetic heritability being what we know it is today—passed on their dominant dark color to offspring in higher numbers (Majerus 2004). Critics of the peppered moth studies enjoy emphasizing that it is the frequency of the appearance of one or the other colored moth that was altered in concordance with the altered environment: darker tree bark and buildings brought about changes in predation, which resulted in a preponderance of darker moths. Yet it is entirely possible in the long term for the peppered moth to revert entirely to the light-winged and light-bodied variety as pollution has abated and environments have been cleaned up.

What if all the dark moths developed a melanic-based disease and completely died off during a time when dark moths otherwise had higher survival rates? The important consideration in this example is that variation in a species is a survival strength, such that species naturally tend toward variation. Indeed, a cleaner English countryside and townships is seeing a resurgence of the lighter-colored moths.

We may attribute our understanding of these genetic mechanisms to Gregor Mendel, who is associated with the discovery and articulation of the fundamental laws of trait heritability through his work on pea plants. It is worth noting that criticisms of Mendel's work are relatively rare, in that Mendel did not associate or disassociate his discoveries with a higher being and drew no short lines between pea plants, monkeys, and human beings.

Gregor Mendel and the Foundation of Heredity

Liu (2005) examined the chronology of historical findings in the fields of biology and genetics to better determine the direction of influence for both Darwin and Mendel. Indeed, the influence that Darwin had on Mendel through The Origin can be seen in the transmittal of the term "gene," which was derived from "pangen," a word coined by Darwin from pangenesis (Liu 2005). Liu (2005) further clarifies the historical relationship between these scientists:

"Darwin was the first to clearly describe almost all genetical phenomena of fundamental importance, and was the first to present a developmental theory of heredity—Pangenesis, which not only greatly influenced many subsequent theories of inheritance, particularly those of de Vries, Galton, Brooks and Weismann, but also tied all aspects of variation, heredity, and development together, provided a mechanism for most of the observable facts, and is supported by increasing evidence" (Liu 2005, 1).

Darwin's Pangenesis and the Search for New Genetic Information

The theory of evolution is based on the natural selection of extant biological phenotypic traits. The process of natural selection, such as described above in the peppered moth example, can only eliminate traits and, perhaps, intensify existing traits. However, natural selection does not, in and of itself, create entirely new traits—a conundrum that requires a different theory to explain how new genetic information comes about.

Darwin's theory of pangenesis was his attempt to offer an explanation for the occurrence of new genetic information that the creation of a new phenotypic variety would require. Theories are, according to the rules of science, intended to evolve, and are, in fact, the building blocks upon which positivist science—truth-seeking empiricism—is constructed, one theory-building step after another. As such, the theory of pangenesis, which was "advocated by Darwin as the main source of genetic variety, has now been empirically disproved" (Bergman 2006). For those who study and follow genetic science, pangenesis is of interest only as a historical theory, except that, as stated, theories have a way of evolving.

Darwin's theory of pangenesis proposed that organisms shed tiny particles called gemmules that transmit heritable characteristics from parents to offspring, and that environmentally altered gemmules will transmit as those modified particles. Francis Galton could not prove Darwin's theory with the science of his day, but new experiments indicate that successful induction of heritable modifications has been conducted. Indeed, "Detection of circulating nucleic acids and prions in plant sap and animal blood is considered as fresh evidence for the existence of gemmules" (Liu 2008). These new discoveries suggest that "a considerable revision of views on Darwin's Pangenesis must occur before a new comprehensive genetic theory can be achieved."

Conclusion: Understanding Evolution Through Historical and Contemporary Lenses

Darwin understood the constraints that common sense and conventional wisdom place on science, citing the ancient adage vox populi, vox dei (the voice of the people is the voice of God) as evidence that popular opinion "cannot be trusted in science" (Darwin 1859). Yet Darwin attempts to frame his argument in a later edition of The Origin, not in scientific terms, but in the lexicon of common sense: