Gregor Mendel, 1822 - 1884

Gregor Mendel


by David F. Coppedge

The story of Gregor Mendel is aggravating. It makes you wonder what might have been, had this Austrian monk encountered Charles Darwin, and had his discoveries become known to the disciples (and opponents) of Darwinism early on (see 10/14/2003 headline). Though the two men may have come within 20 miles of each other one day, historians are fairly certain that Darwin was unaware of Mendel, though Mendel knew of Darwin. Mendel believed that the laws of genetics he deduced just seven years after Darwin’s Origin of Species was published posed a serious challenge to the theory of “transformism” (that one species can be transformed into another).

It is also aggravating, in retrospect, to see how Mendel’s discoveries were treated once they did become known. “Ignored” is the word most often used in history books to describe the early reception of his paper. As we shall see, nearly 72 years went by before it was no longer possible to ignore Mendel’s findings. By then (the 1930s), Darwinism had triumphed in the Scopes Trial, had a full head of steam and was unstoppable. It just became a matter of fudging Darwinism enough to massage Mendelian genetics into it. These days, the neo-Darwinists tend to claim Mendel as their own, but the evidence shows that the creationist monk would have been offended by any such association. Nigel Williams, writing in the October 14, 2003 issue of Current Biology, stated that “Once Gregor Mendel is placed back into the intellectual landscape that he would himself recognize,” it was clear that he would have “seen The Origin of Species as a challenge to his own worldview.”

Gregor Mendel, a Catholic creationist, believed he had demonstrated that species are resistant to change, because characters are inherited without alteration throughout generations. This was a novel idea to breeders of the day. No one knew just how characteristics were inherited. Common experience showed that children resembled their parents, but how did the various traits get sorted out in the union of sperm and egg?  Why were some crosses of plants or livestock sterile, and others fertile?  Darwin toyed with a hypothesis he called pangenesis, which assumed that traits from all over the body somehow flow into the gametes. A common misconception of the time was that traits were blended in the offspring, rather than remaining discrete units (by analogy, compare mixing two fluids versus mixing two jars of colored marbles). Darwin’s theory demanded that variations be heritable, and that traits be fluid enough to evolve so that they could be acted on by natural selection. If the traits remain unchanged, like the colored marbles, how could new variation arise?  Each generation would just get a different ratio of static, unchanging characteristics.

Working in the gardens of the Monastery of St. Thomas in Brunn, Austria, Gregor Mendel demonstrated exemplary scientific technique. His work is often cited as a textbook example of the experimental method. It required patience, attention to detail, careful record keeping, and interpretive insight. In a project spanning ten years, Mendel crossed 28,000 plants of the common garden pea, Pisum, and charted the inheritance of seven selected traits:

  1. seed texture (wrinkled or smooth)
  2. albumen color (yellow, orange or green)
  3. seed coat color (green or yellow)
  4. pod form (inflated or deflated)
  5. pod color (yellow to green)
  6. flower position (axial or terminal)
  7. stem length (6 ft or taller vs. 1 foot or shorter)

He chose peas as his subjects because they have a short season, are easily pollinated, have clearly recognizable traits and can be protected from cross pollination. He spent the first two years carefully breeding pure stock that were true to type, then spent eight more years cross-pollinating the types and counting the traits found in the offspring. His procedural diligence and accurate record-keeping were unexcelled, but even more important, he had a goal, executed a plan, and understood the results. Mendel found principles of inheritance that made testable predictions, and formulated them in mathematical terms. Without knowing about chromosomes or the details of cell division, he had discovered the laws of genetics.

The three laws Mendel deduced seem common-sense now, but were radically new in his day:

  1. Law of Paired Factors (Genes): Traits come in pairs (alleles), and each parent contributes just one of the alleles. A trait, such as seed coat color, is contributed by both parents: i.e., it is not one sex that determines seed color; the egg and the sperm both contribute half of any given trait. (Some traits, of course, are sex-linked traits, such as those on the Y chromosome in mammals.)
  2. Law of Dominance: In a pair of genes (genotype), one allele will dominate the other and control the outward appearance (phenotype). Mendel invented the terms dominant and recessive to explain this law. For instance, smooth is dominant over wrinkled; if an offspring has one allele for smooth and one for wrinkled, the resulting offspring’s seeds will appear smooth, even though an allele for the wrinkled trait is present in the genotype.
  3. Law of Segregation: Traits are inherited independently. A seed can be wrinkled and yellow, wrinkled and green, smooth and yellow, or smooth and green. The traits are sorted independently, by chance, into the offspring, but enough trials will show they obey mathematical ratios. (Later geneticists found that some traits are linked and inherited together.)

Beyond the mere statement of these principles, Mendel invented terminology that made future work productive. He used capital letters for dominant traits, and lower-case letters for recessive traits. Let A represent the dominant trait for smooth seed coat, for instance, and “a” represent the recessive trait for wrinkled coat. If an AA plant is cross-bred with an aa plant, according to Law 1, each plant will contribute one allele via either pollen (male) or ovum (female). The offspring could, therefore, be AA, Aa, aA, or aa. According to Law 2, what the botanist will observe is three plants with smooth seeds (AA, Aa, aA), and one with wrinkled, in a 3:1 ratio, but the actual genetic ratio is 1:2:1. One will be homozygous dominant (AA), two will be heterozygous dominant (Aa, aA), and one will be homozygous recessive (aa). It’s in the third generation where things get interesting. Let the two heterozygous plants (Aa and aA) be crossed, and if enough experiments are done, they will again sort into AA, Aa, aA, and aa (1:2:1). But what the botanist will have observed, counter to intuition, is two smooth-seed plants breeding, and one-fourth of them coming out with wrinkled seeds! Mendel had the insight to see what this meant: the recessive traits were always present, and their alleles were being faithfully transmitted through three generations without alteration.

Mendel’s laws can be extended to calculate expected ratios for combinations of traits. Let Bb, for instance, indicate dominant and recessive alleles for seed color. If AABB is crossed with aabb, then according to Law 3 (independent assortment), the offspring might be AABB, AABb, AAbB, AAbb, AaBB, Punnet SquareaABB, aaBB, and so forth. This can get confusing, but makes sense when put into a diagram called a Punnet Square, with one trait on the vertical axis and one on the horizontal, and all the assorted mixtures shown in the boxes. The main point is that each trait (seed texture and seed color) is inherited independently of the other, and the ratios follow mathematical laws. Most important, the traits pass unchanged throughout generations. These findings spelled the end of speculations, shared by Darwin and most others, about blending inheritance.

Mendel’s epochal paper, “Experiments in Plant Hybridization,” completed in 1865 and published in 1866, is a long and detailed analysis that stands as a monument to quality scientific investigation. It is now available in English on the internet at Mendelweb.org. With good scientific caution, Mendel avoided overinterpretation. He said, “It must, nevertheless, not be forgotten that the explanation here attempted is based on a mere hypothesis, only supported by the very imperfect result of the experiment just described.” He encouraged others to perform additional experiments, but in the years since, it has been difficult for anyone to match his high standards.

So why was this important paper ignored? Some think it escaped notice because it was published in an obscure Austrian journal, but this is an insufficient excuse. Mendel attempted to make it known by sending copies to prominent scientists. To Carl Nageli, for instance, called “a celebrated botanist and authority on evolution” in the anthology Great Experiments in Biology (Prentice-Hall, 1955), Mendel wrote in 1867, “I have never observed gradual transitions between parental characters or a progressive approach toward one of them.” He defended his laws as being based on experiment, avoiding any philosophical speculations. But he knew the import of his laws. At the end of his great paper, he commented on the work of a predecessor, which his work corroborated:

Gartner, by the results of these transformation experiments [i.e., attempting to change one species into another], was led to oppose the opinion of those naturalists who dispute the stability of plant species and believe in a continuous evolution of vegetation. He perceives in the complete transformation of one species into another an indubitable proof that species are fixed with limits beyond which they cannot change. Although this opinion cannot be unconditionally accepted we find on the other hand in Gartner’s experiments a noteworthy confirmation of that supposition regarding variability of cultivated plants which has already been expressed.

Mendel listed some of the species Gartner experimented on. The final sentence of his paper states, “hybrids between these species lost none of their stability after 4 or 5 generations.” In a day where Darwinism was sweeping the intellectual world in Britain and spreading to the continent, Mendel’s words quoted above seem intended as a clarion call to observation over speculation. He seems to be shouting, in his own gentle way, Species do not transform one into the other. They show stability from generation to generation, and my experiments demonstrate that fact. Isn’t anyone listening?

It can only be assumed that they were not listening. Inebriated on the elixir of a naturalistic mechanism for transformism, what use did they have for a few uncomfortable facts printed by a monk in Austria? Mendel’s work was available for study by anyone who cared to look, but it was virtually forgotten till 1901. Back in 1865, a new day was dawning, a day that liberated science from its hard slavery to experiment. Mendel belonged to the old school of scientists that believed in the experimental method. But now, storytellers were free to speculate wildly about the unobservable past and future and call it science.

Gregor Mendel’s life shows that a devoutly religious person, who has devoted his life to his beliefs, can also be interested in science and contribute to scientific discovery in a profound way. He probably gained his interest in science, and appreciation for the rigor of experimentation, while a student under Christian Doppler (for whom the Doppler Effect is named). Although Mendel is best known for his work on heredity, he also was interested in meteorology and astronomy. Dan Graves in Scientists of Faith provides a good synopsis of the life of Mendel, including many interesting facets before and after his work on garden peas. While it can be safely assumed Mendel was a learned man, had a penchant for detail, and was patient and persistent by nature, he also had a heart for people. He could be easily overwhelmed in his empathy for others. He never lived to see, however, his scientific work taken seriously. Thirty-five years would pass before its “rediscovery.”

In 1901, Hugo De Vries, among others, found Mendel’s paper and was immediately impressed. He shared it with a number of important biologists. He seemed to realize, also, that it posed a challenge to Darwin’s theory of natural selection, by ostensibly not providing the variation needed on which selection could act. His oft-quoted remark, “natural selection can explain the survival of the fittest, but not the arrival of the fittest,” encapsulates the problem. During the first few decades of the 20th century, evolutionary theory was in a malaise. Mendel’s Laws were now acknowledged, but evolutionists were not quite sure what to make of them. Another 37 years would pass before the evolutionists seriously made an attempt to bring Mendel and Darwin together. Meanwhile, the Scopes Trial of 1925 convinced most in the news media and popular culture that Darwinism had triumphed over religious “fundamentalism.”

In the 1930s, geneticists attempted to scale the hurdle Mendel had erected. According to De Vries, genetic mutations provided the variation needed for evolution, and the new theory basically assumed mutations provided variation, and natural selection acted on those variations, producing great transformations gradually over millions of years. The “synthetic” theory of evolution, or “neo-Darwinism,” was born. Having breathed new life into evolutionary theory, it seemed to satisfy most evolutionary biologists; so much so, that by the Darwin Centennial in 1959 (the 100th anniversary of the publication of On the Origin of Species), Julian Huxley stated that Darwin’s theory of evolution had reached the status of undisputed fact, and that all of the universe was describable as a single, continuous process of evolution. The euphoria was not to last. Mathematical challenges by Sir Peter Medawar and others cast serious doubt on the ability of neo-Darwinism to produce substantive changes.

By the 1980s, evidence for a discontinuous record in the fossils and in the genes divided the Darwinians into the “gradualist” and the “punctuationist” camps. Stephen Jay Gould and Niles Eldredge, in particular, angered their gradualist foes by arguing that evolution occurred in fits and starts. The debate continues to this day. The late 20th century saw an explosion of knowledge about genetics. It became possible to trace the actual genes, letter by letter, in the genetic code, and watch the sorting of alleles into the gametes. One thing became clear: cells are fastidious about ensuring genes are accurately copied and distributed without error.

Comparative genomics has shown that mutations do occur, and that the same gene in different animals may show numerous differences, while others are “highly conserved” or virtually identical. In some cases it is possible for individual DNA letters to mutate without damage; there is a certain amount of resiliency in the genetic code, such that a single mutation might not produce any functional change. These are called neutral mutations. Also, elaborate proofreading mechanisms were discovered, showing that cells have many ways to correct mutations. Numerous mutations have been shown to cause disease or death, but to this day, biologists have been unable to show a clear case of a mutation leading to a new species, or even an undisputed benefit that would provide fodder for natural selection.

Most examples put forward of favorable mutations would be beneficial only in isolated environments, with a net fitness cost to the individual (such as the mutation that leads to sickle-cell anemia; it provides some resistance to malaria, but would otherwise certainly be characterized as a deleterious mutation). Numerous attempts to induce mutations, especially on the fruit fly Drosophila, have been neutral at best, and generally detrimental or lethal. Furthermore, figuring out how a theoretical beneficial mutation might become established in a population, given Mendel’s laws, has proved elusive. As of the early 2000’s, a growing number of scientists were wondering whether natural selection – the principle that made Darwin famous – is even effective in biological evolution at all. Nothing offered to replace it, however, has survived any rigorous experimental test. The upshot of this overview of subsequent history is that Mendel’s Laws stand, while Darwin’s speculations teeter on the brink of collapse.

A museum has been erected in Mendel’s honor at the monastery at Brunn, Austria, where he did his famous experiments. Despite the explicit wishes of the abbott of the monastery, however, the display ignores the religious side of Mendel’s life and focuses exclusively on the experimental work (see 05/15/2002 headline). The abbott succumbed to a year of pressure and misinformation against him, only submitting to the secularized display by gaining a promise to hold an annual workshop on bioethics at the site. This shameful rewriting of history will succeed only if we allow it. People interested in the history of science should be told, emphatically, that the laws of genetics were discovered by a creationist who understood the Genesis statement, Let them bring forth… after their kind.

For further research on why Mendel was ignored for so long, see a paper by Loennig in German with an English summary here.