Darwin’s Unproven Hypothesis
Darwin had put forth his theory not as a proven fact, but as a probable hypothesis. He had inferred speciation hypothetically from evidence, not demonstrated it beyond all doubt. He was not naïve about the magnitude of the difficulties he faced in persuading skeptical colleagues who felt that his theory was simply too speculative, too far removed from hard observational facts. “Although I am fully convinced of the truth of the views given in this volume,” he stated honestly, “any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject my theory” (Origin of Species, pp. 481-2). Indeed, many thought that he had gone too far, and in some cases Darwin even modified his theory in response to critics.
Enter Fleeming Jenkin
One of Darwin’s most astute critics, the Scottish engineer Fleeming Jenkin, was a man of many talents. Owner of thirty-five patents (mostly on telegraph cables and telpherage), many in partnership with his close friend, the great physicist Lord Kelvin, Jenkin was a highly accomplished engineering professor. He also contributed to public health and did distinguished work on price theory, trade unions, and taxation, essentially originating graphical analysis of the law of supply and demand—not to mention essays about drama and stage productions.
A former religious skeptic turned Christian, Jenkin is probably best known today for his review of the second (1860) edition of The Origin of Species. Of the many objections he advanced, I will present three—all of which are still popular in one form or another with opponents of evolution.
Do Variations Accumulate Without Limit?
I’ll start with the very interesting argument that variations among animals and plants tend toward an asymptotic limit, denying the possibility of complete common ancestry. As Jenkin described it,
“Darwin’s theory requires that there shall be no limit to the possible differences between descendants and their progenitors, or, at least, that if there be limits, they shall be at so great a distance as to comprehend the utmost differences between any known forms of life. The variability required, if not infinite, is indefinite.”
In making his objection, Jenkin offered an example from breeding race horses—a common activity in the British Isles. “We all believe that a breeder, starting business with a considerable stock of average horses, could, by selection, in a very few generations, obtain horses able to run much faster than any of their sires or dams,” but eventually any improvements in speed would be almost negligible, despite the diligent efforts of many breeders to obtain the fastest horses. Overall, “the rate of variation in a given direction is not constant, is not erratic; it is a constantly diminishing rate, tending therefore to a limit.”
Jenkin’s insistence on inherent limits for biological variation is echoed today when creationists say that biological variation must take place within the boundaries of the original created “kinds,” whatever they actually were. They do not agree with BioLogos that the genetic evidence for common ancestry is enormous—evidence entirely lacking to Darwin and Jenkin.
How Do New Organs Originate?
Jenkin added a second objection pertaining to variations: although natural selection might improve already existing biological organs, it cannot “create or develop new organs, and so originate species.” Jenkin believed that the formation of a new organ started with a sudden jump—the birth of a mutant individual, what was then called a “sport”. However, according to the non-Mendelian view of inheritance held by Darwin, Jenkin, and many others at the time, often called “blending inheritance,” any advantage associated with the unique trait of a single individual would be diluted every time it breeds with other individuals lacking that trait. In just a few generations, the effect would be “swamped” into insignificance, as the advantage resulting from the mutation is repeatedly cut in half.
Jenkin illustrated this point using the extremely racist example of a white man who finds himself shipwrecked on an island occupied by black people. According to Jenkin, even after many generations of interbreeding, the inhabitants of the island would still not be white; quite the opposite: the presumed “physical strength, energy, and ability of a dominant white race” would gradually diminish. As Jenkin put it, “In the first generation there will be some dozens of intelligent young mulattoes, much superior in average intelligence to the negroes,” but over time “by degrees this advantage wanes.” (The egregious racism evidenced in this example–the only one he offered to illustrate this particular point–was common at that time.)
We now know that blending inheritance is wrong, and that Mendel’s work eliminates the problem of “swamping”. Once a given trait appears in a population, its associated gene(s) will be passed on and the trait can be expressed undiminished in future generations. For example, a person with piercing blue eyes who marries a person with brown eyes can have descendants with the same blue eyes. The trait is not “blended away” or diluted in the process of reproduction, whether or not it manifests itself in the very next generation.
Nevertheless, modern genetics does not erase all of the questions about how new organs can be formed by Darwinian evolution—as contemporary opponents of Darwinian evolution like to emphasize. For example, the book, Darwin’s Black Box (1996), written twenty years ago by biochemist Michael Behe, argued that no one had yet demonstrated exactly how Darwinian pathways could account for the “irreducible complexity” of the bacterial flagellum (a structure analogous to an outboard motor on a boat) or the immune system. However, we now know that neither the flagellum nor the immune system is irreducibly complex. Even something as complex as the mammalian eye can be understood in terms of Darwinian evolution.
Not Enough Time for Evolution to Happen
The age of the Earth could not be calculated very precisely until around the time when Darwin published The Origin. Geologists had known for decades that the Earth must be enormously older than the traditional biblical timescale of a few thousand years, but they didn’t agree on any particular estimate. From Charles Lyell Darwin had acquired a vague sense of the vast antiquity of the Earth, but in The Origin we find just one place where he assigned a specific number to a geological process. According to Darwin, about 300 million years was needed to form the Weald, the chalky region in southeastern England that culminates in the famous white cliffs of Dover. It was in fact a crude, back-of-the-envelope calculation, yet he said that it “must have required 306,662,400 years,” implying a precision that simply wasn’t there and leaving the reader with the impression that the Earth itself was even far older, old enough to allow for evolution to proceed at a snail’s pace (Origin, p. 287).
This did not convince Jenkin, whose quantitative skills far exceeded Darwin’s. He drew on state-of-the-art calculations by his friend Lord Kelvin, establishing the range of possible ages for the Earth and the Sun. The Earth, he believed, was between 20 and 400 million years old, most likely about 98 million years old; the Sun was probably about 100 million years old, with an upper limit of 500 million years. If Kelvin was right, then Darwin was wrong: there wasn’t nearly enough time for evolution to have happened as Darwin conceived it.
Subsequently, however, we’ve learned that the Earth is billions of years old, nullifying Jenkin’s objection. Of course, we can’t blame Jenkin for being ignorant. Indeed we should credit him for granting the abstract possibility that “it may please the Creator to continue creating energy in the form of heat at the centre of the sun and earth…” He simply had no way to know that the Creator was doing exactly that, by putting nuclear fusion inside the Sun and radioactive decay inside the Earth.
Old-earth creationists today accept an ancient Earth, but still doubt that evolution could have produced the full range of living things without some acts of special creation. Young-earth creationists obviously reject the standard timescale entirely. However, they actually agree that natural selection can form new creatures—even far more rapidly than evolutionists grant—but (again) only within created “kinds.”
Jenkin’s Conclusion and Darwin’s Response
At the end of his review, Jenkin stated his conclusion succinctly: “A plausible theory should not be accepted while unproven; and if the arguments of this essay be admitted, Darwin’s theory of the origin of species is not only without sufficient support from evidence, but is proved false by a cumulative proof.”
How did Darwin respond to arguments like these?
Darwin didn’t know how to refute Kelvin’s arguments about limited time—and he was really concerned about them, telling Alfred Russel Wallace in 1869 that “Thompson’s views of the recent age of the world have been for some time one of my sorest troubles.” Darwin thought he was still correct, but he could not back it up with a formal quantitative argument. Therefore, starting with the third edition of The Origin in 1861—even before Jenkin wrote his review of the second edition—he ducked the issue by removing the part about the denudation of the Weald.
Ignorant of Mendel’s work and looking for ways to quicken the process of evolution, especially if the Earth is really much younger than he thought, Darwin introduced his theory of “pangenesis” in another book, The Variation of Animals and Plants Under Domestication (1868). He postulated that particles called “gemmules” would be emitted by parts of the body and circulate through the bloodstream to the reproductive organs, where they would accumulate and influence heredity. In that way, characteristics acquired by an individual organism during its lifetime could perhaps be inherited by its offspring, enabling evolution to work faster that it would otherwise. The inheritance of acquired characteristics is usually associated more with one of Darwin’s predecessors, the French marine biologist Lamarck, than with Darwin, but Darwin nevertheless used that idea to some extent.
For several decades other scientists proposed various Lamarckian ideas, underscoring an irony: although Darwin’s evidence eventually convinced others to accept evolution, the most widely accepted varieties of evolution at the time were neo-Lamarckian. Darwinian evolution, driven primarily by natural selection operating on “random” variations, did not gain the allegiance of a majority of scientists until around 1930. This phenomenon has been called “the eclipse of Darwinism,” but exploring that topic would take us well beyond the scope of this series.
Today, the vast majority of biologists and geologists, whether or not they are Christians, believe that Darwin’s central idea was right—widely diverse organisms are related through common ancestry, and natural selection is a primary cause of that diversity. Many of the explanatory problems that Darwin, Jenkin, and others found in certain details of his theory have been solved or made irrelevant by subsequent scientific discoveries.
Overall, the story of Darwin and his theory shows that details matter—not only in science, but also in history. Darwin didn’t invent the idea of evolution and did not believe it at first, but he came round to it after extensive observations and experiences on a five-year voyage around the world led him to wonder about the “mystery of mysteries”—the origin of new creatures through vast geological ages. Drawing key insights from economic theory, he conceived a new type of evolutionary theory driven by competition for scarce resources—all the while viewing it as a process of creation by natural law.
Even if Darwin wasn’t right about every single detail, he was right about the big picture: God does indeed create many things in ways that are not entirely above human understanding. We should rejoice and be glad in this: the study of evolution is just one more way to think God’s thoughts after him.