The Legacy of Charles Darwin

By

David A. Stelzig

"…it would seem to require a greater infinity of power to cause the causes of effects, than to cause the effects themselves" Erasmus Darwin, 1794

     Rain, gentle but steady, chilled the air and decreased visibility early in the evening of October 2, 1836, but lights of Falmouth finally twinkled on the horizon and quickly brightened as His Majesty's Ship Beagle soundlessly approached, then dropped anchor in the safe waters of the harbor. Only then did huzzahs and laughter roll from the deck of this tiny ninety-foot sailing vessel.

     Charles Darwin was about to set foot on soil of his native England for the first time in half a decade. He had spent five years observing, chronicling, and sampling the geology and biology of lands in the southern hemisphere, including the Galapagos.

     Darwin's specimens, along with written and oral discussions of his findings, would bring him fame. He would be praised both in person and print. He would be voted a member of The Royal Society.

     But Darwin was not well. Indeed, for the rest of his life, he endured chronic depression, indigestion, and headaches so severe that he was confined to bed for months at a time. The cause of Darwin's illness? No one is certain. Lactose intolerance has been suggested. So has some rare tropical disease. However, most scholars think the explanation is at least partially psychosomatic.

     Simply stated, Darwin was racked with guilt because he was burdened with a frightening secret. Darwin knew--he was absolutely sure that he knew--species in existence today were not created by God.

     It was not only that Darwin saw changes in species, or even the appearance of new ones. Other free-thinking scientists and philosophers--including Darwin's grandfather, Erasmus--had already suggested that species were mutable. But this was just taken as evidence of God's direct hand in the continuing process of creation. The Garden of Eden remained Gospel. Man was still the only animal infused with an everlasting soul.

     Darwin's sin was that he concluded these changes occurred by a process that precluded the direct involvement of God. They had come about by natural selection: random changes in earlier species had made the organisms more fit to survive and so these changes were passed on. Eventually, an accumulation of such changes made the subsequent progeny so different that they were, in fact, new species.

     And not just some species. All species. If this mechanism worked for the finches and tortoises of the Galapagos, it also worked for man.

     Darwin's theory of natural selection didn't come as an intuitive flash on the Galapagos. He returned to England, awed by the diversity of organisms he'd seen, but believing an all-powerful God had created them to perfectly fit their unique environments. Then, five months after Darwin's return, ornithologist John Gould informed him that his collection of Galapagos songbirds included as many as twelve varieties of ground finch, all slightly different from the finches of South America. Darwin had been careless in tagging his own specimens, but with the aid of more carefully labeled collections from Captain FitzRoy and crew members of the Beagle, he was able to determine that his finches were segregated by type on the individual islands of the Galapagos. He started to think he was on to something truly new.

     Darwin theorized that continental finches somehow became isolated on the Galapagos and were thus subjected to the harsh conditions of these islands. Many were unable to survive. A few, however, transmuted into more fit species and therefore became the dominant populations.

     Darwin soon became convinced of the validity of natural selection, but was not yet willing to publish. Some have suggested this reluctance was partially due to the widespread condemnation of Robert Chambers' 1844 anonymous essay, "Vestiges of the Natural History of Creation." More likely, if this primitive argument for evolution had any effect on Darwin, its absence of scientific support merely galvanized his natural tendency toward meticulous documentation.

     Whatever the reason, Darwin discussed his theory with friends, but didn't publish. Not yet. He had planned to polish the writings about his terrible knowledge for another two years, but then, in 1858, he received a manuscript in which Alfred Wallace outlined a mechanism for the appearance of new species nearly identical to his own theory of natural selection. At the time, Darwin was despondent about his eighteen-month-old son, Charles Waring Darwin, who succumbed to scarlet fever on June 28, and so he asked his friends, Charles Lyell and Joseph Hooker, to decide how to handle the matter. They quickly agreed on simultaneous publication. On July 1, 1858, the theories of Darwin and Wallace were presented in a single reading to the Linnean Society of London.

     A little over a year later, in November 1859, Darwin published "On the Origin of Species by Means of Natural Section, or the Preservation of Favoured Races in the Struggle for Life," a more complete discussion of his theory and arguably the most important biology book ever written. Largely because of this wildly popular text--the entire printing sold to wholesalers in a single day--evolution soon became mainstream science.

***

     Other mechanisms have been proposed to help explain evolution, but natural selection is still considered a mainstay of the process. Indeed, creationists frequently argue interchangeably against evolution and natural selection, believing, with some justification, disproving either will disprove both.

      That was an easier task for Darwin's contemporaries because the laws of heredity were not understood. The concept of molecular biology could not even be imagined. Since Darwin, however, considerable scientific data have accumulated that support the theory of natural selection. Gregor Mendel, for example, in his landmark studies of the garden pea, demonstrated that discrete units of genetic information are passed with mathematical precision from parent to offspring. These units of information, now known as genes, were shown to be DNA. And, in 1953, in a laboratory at the University of Cambridge, a scant seventy-five miles north of the ancestral home in which Darwin wrote "Origin," physicist Francis Crick and his graduate student James Watson determined the three-dimensional structure of DNA.

     To most biologists, the Watson-Crick model made it intuitively obvious that genetic information in the long DNA polymer is due to the sequential order of the subunits. It is as if DNA is a long chain made up of links of four different shapes.

     Building on this metaphor, replacing a square link for one that's round in the DNA chain responsible for flower color might be enough to change the bouquet from pink to white. Likewise, substituting a couple triangular links for square in one year, a round link for oval many years later, and a few oval links for triangles, after another million years or so, could cause an organism to become an entirely new species.

     This metaphor is a simplistic illustration of point mutations, one mechanism used in natural selection. An example is sickle cell anemia, a genetic disease that's a blessing in disguise: people who inherit this disease have a significant resistance to malaria, a more deadly disease. Not coincidentally, sickle cell anemia only occurs in people who live--or whose ancestors lived--in areas where malaria is prevalent.

      Sickle cell anemia is caused by a point mutation in a recessive gene containing the DNA with the blueprint for the synthesis of hemoglobin, the red blood cell protein that carries carbon dioxide and oxygen to and from the lungs. One subunit of that DNA has a shape (adenine) substituted by another (thymine). Hemoglobin synthesized from this faulty blueprint has the hydrophobic amino acid valine on the surface of the protein rather than the water soluble glutamic acid, and these abnormal hemoglobin molecules tend to clump together in an effort to get the valine out of contact with the aqueous environment of the cell. If a child receives the sickle cell gene from both parents, this clumping is so severe that the hemoglobin forms long chains that push the red blood cell into a sickle shape, resulting in early destruction of the cell and, often, death of the individual. However, it is much more likely for a child to receive the sickle cell gene from just one parent, in which case there are essentially no symptoms of anemia. More to the point, if an infected mosquito injects that child with the malarial parasite, he may become sick but will almost certainly survive. In contrast, without the sickle cell mutation, death would have been highly likely.

***

     Point mutations are not the only genetic changes involved in natural selection. Another is jumping genes (transposons), the discovery of which earned Barbara McClintock the Nobel prize in 1983. If point mutations are considered one-letter changes in the genetic code, jumping genes are whole words, sentences, or paragraphs that have moved from one location in a chromosome to another. This can be within a single chromosome, from one chromosome to another, and even between species, for example from an invading virus to the genes of its host. A measure of the significance of this process in evolution is the estimate that as much as 45% of the human genome originated as jumping genes.

***

     Natural selection is an essential piece of the evolution puzzle, but not the only one. Another, genetic drift, is considered by many scientists to be at least as important.

     Natural selection explains nonrandom shifts in a population due to point mutations and other gene modifications. It is survival of the fittest. In contrast, genetic drift is survival of the luckiest. It is caused by a random event in a population which results in a change in the gene pool of that population. Consider, for example, an isolated group of people in which only one couple has the genetic ability to give birth to a blue-eyed baby. If they never have children, or if all their offspring die without giving birth, the genetic blueprint for blue eyes will immediately disappear from that population. Real life is more complex of course and it takes numerous generations for a genetic trait to drift out of--or to become established in--the total gene pool.

     Genetic drift doesn't usually have much effect in a large population because random changes, like the relative number of brown- and blue-eyed babies, tend to average out. But in small populations the effect can be profound.

     Small populations can arise in many ways. A typhoon can blow songbirds to distant islands. Religious people, such as the Amish, can segregate themselves from society. Advancing glaciers of an ice age can divide a population into two or more small groups. Whatever the cause, radically decreasing the population size significantly increases the importance of genetic drift.

     Creationists don't usually pay attention to the concept of genetic drift. This is at least interesting, considering that many of them believe the story of Noah and his ark, which, if true, would be the granddaddy of all population decreases.

***

     It has been one-hundred-fifty years since Darwin published the first edition of "Origin." During this time, an overwhelming body of evidence has accumulated in support of the theory of evolution. In contrast, experimental evidence of creationism has been zero. Because of this, the percentage of credible scientists arguing against evolution has become vanishingly small.

     And yet, that number is not zero.

     One of the more common claims of creationists is that anything exceedingly complex presupposes the existence of a creator. Theologian William Paley first made this argument in 1802 by stating the existence of a pocket watch proves there is a watchmaker because the individual components could not have come together accidentally. A recent biological example of this argument of "irreducible complexity" is the flagellum, a whiplike appendage used for locomotion by some bacteria. The flagellum is composed of as many as thirty distinctly different proteins. Creationists have argued that since none of these proteins have any other function, they must have been created as a working flagellum. Like the pocket watch, the flagellum could not have happened accidentally.

     But some organisms have functioning flagella that are relatively simple. It is now also known that some pathogenic bacteria have a handful of proteins nearly identical to those of complex flagella that function not in motility, but rather in the injection of toxins into the cytoplasm of their hosts. It is conceivable that these "membrane transport machines" served as evolutionary precursors to the more complex flagella.

     Creationists try to debunk evolution by stating that it can't explain the origin of life. Some laboratory experiments have shed light on how components of DNA and proteins, and even membrane-bound organelles, might have originated on a prebiotic earth, but it's true that the origin of life is still a mystery. It can even be argued that the existence of life on earth supports a belief in a creator--or an ancient visit by aliens. But it isn't evidence. Furthermore, it has nothing to do with the multigenerational evolution of a biological organism into a new form.

     The second law of thermodynamics states that in a closed system there cannot be a decrease in randomness (entropy). Creationists sometimes say that thermodynamics proves man could not have evolved from more random organisms. But suggesting this while ignoring energy sources that fuel evolution--such as food digestion and, ultimately, nuclear fusion of the sun--is no more logical than ignoring human muscle and man-made machines and deciding that a pocket watch is much too complex to exist.

     Some creationists think it mathematically impossible that complex molecules, let alone organisms, came about by chance. They sometimes use Shakespeare's, "To be or not to be," as an illustration. Randomly selecting one letter every second, it would take longer than our earth has existed to come up with the correct spelling of this thirteen-letter phrase. But of course that's not how evolution works. Existing molecules--and, yes, organisms--evolve by chance additions or changes, but they don't throw out the past until something better happens along. In the Shakespeare example, if incorrect letters are discarded and correct ones kept, "tobeornottobe" could be written in less than six minutes.

***

     Creationists have other ostensibly scientific arguments in their arsenal, but they are no more threatening to the theory of evolution than the ones discussed here. So what argument does that leave? Religion. Christianity, Islam, and Judaism all teach that man was created by a God and that playing by the rules will earn man the right to live with that God for all eternity. We are simply too egotistical to believe that a loving God would be so insulting that He would create us in His image by letting us evolve from some stupid and soulless animal.

***

     Evolution doesn't preclude the existence of God. Or even the infusion of an eternal soul at a key point in the development of some prehistoric primate. And the evidence supporting evolution is vast. Nonetheless, creationism is still widely believed by many people. This is especially true in the United States, and that fact may hold some explanation to this enigma.

     According to a recent survey, only approximately 40% of Americans believe in evolution. In Europe, the number is closer to 80%. To a large extent, this correlates with the presence of fundamental Christians in the United States who view the Bible as the literal word of God. In contrast, European Protestants and mainstream American Protestants consider Genesis to be metaphorical.

     The conservative wing of the Republican Party, especially in recent years, has contributed to the problem by making opposition to evolution a prominent part of their campaigns.

     Finally, many in the United States have a poor understanding of modern genetics. For example, in one survey, fewer than half of American adults were able to provide even a minimal definition of DNA.

***

     In Darwin's age, individuals who didn't believe in evolution called themselves "creationists." That's an honest title and they were honorable men. They made their arguments using accepted science of the day and they did this in scientific publications and at meetings of fellow scientists.

     In the United States, twentieth century creationists focused their fights against evolution in the courtroom. In one notorious example, John Scopes was found guilty, in 1925, of teaching evolution to his high school students. The Tennessee law he violated was declared unconstitutional, but not until the 1960's.

     Also in the 1960's, the term, "creationism," morphed into "scientific creationism" and a few school boards required this belief to be taught along with the teaching of evolution. When tested, these laws were found to be religious and thus have been declared unconstitutional.

     Most recently, creationism has been called "intelligent design'" as in the phrase, "the science of intelligent design." And again, because of the constitutional requirement for the separation of church and state, laws requiring the teaching of intelligent design have been declared unconstitutional.

***

     The creation/evolution debate will certainly continue. That's all right. Creationists could even be correct. But if so, creation must be by some mechanism that includes evolution because this science is testable and has been tested. It is still considered a theory only because exact details haven't been worked out, but the overall concept of evolution is a proven scientific fact.

---

David A. Stelzig is a retired professor and Chairman of Agricultural Biochemistry at West Virginia University. Stelzig has numerous research publications in refereed journals, including Science, Plant Physiology, and Phytochemistry. He also has short fiction published in Boston Literary Magazine and DiddleDog, and stories accepted in Midnight Showcase and an anthology of MD authors, but “Legacy” is his first piece of creative nonfiction.