What particularly fascinated Gregor Mendel was the way in which the plants handed on their characteristics to the next generation. “What could happen,” he thought, “if I crossed a white-flowered plant with a red-flowered? Would the next generation have red flowers or white? What if I crossed a tall plant with a short one? What height would the offspring be?”
As Mendel performed these experiments and carefully analyzed the results, he realized that he had discovered some fundamental laws concerning inheritance. Greatly excited, he published his findings in a scientific journal—but the scientific world ignored Mendel’s work completely. Discouraged, he abandoned his research. When he died in 1884, Mendel had no idea that 20 years later, he would have become world famous as the founder of a new science. Mendel’s work is now regarded as the beginning of the science of genetics, the study of inheritance.
In the preceding chapters we have looked at the rise of evolutionary theory and the evidence of the fossil record. Now we must consider whether—as is generally claimed—the findings of genetics support the idea of evolution.
Mendel published his findings in the late 1860s at just the time when Darwin’s theory was becoming immensely popular. Mendel published in a reputable journal and his paper was widely circulated and certainly known about. Yet it was not until 1900, 16 years after Mendel’s death, that the work was rediscovered and its importance realized.
Why were such vital discoveries ignored? The answer almost certainly is that they conflicted with Darwin’s theory of evolution. This is seldom admitted today, yet it is still true that what Mendel discovered disproved one of Darwin’s most important assumptions. This is demonstrated by the fact that after Mendel’s work was rediscovered, Darwinian evolution suffered a temporary eclipse. After a while, evolutionary thinking re-emerged in a slightly different form which was said to be quite consistent with Mendel’s genetics. As we shall see, however, the two are not consistent and both cannot be true.
What did Mendel discover that spoke against Darwin’s theory of evolution? This can best be answered by considering what he actually did. Mendel crossed various races of edible peas. When a red-flowered plant was crossed with a white-flowered, the offspring were found to be red-flowered. Mendel then crossed these red offspring with each other and found that they produced offspring of their own in the ratio of 3 reds:1 white.
We can best understand this by considering the genes involved in these crosses. A gene can be considered as a unit which determines a particular characteristic, in this case flower color. It can exist in one of two forms, one giving rise to red flowers and the other to white. The offspring of the original cross of red-flowered plants with white were all red-flowered, although they did in fact possess both a gene for red-flower and a gene for white.
Mendel concluded that the red gene must be dominant to white, so that any plant that possessed them both would be red. When these red plants were bred with each other, it was possible for two white genes to come together and so give offspring that were white. The chance that the offspring would receive at least one red gene is 3:1, as the diagram shows below.
Mendel found that when he interbred the red-flowered plants obtained as the offspring of his original cross, he got white flowers as well as red. Darwin’s theory rested on the assumption that in such a case as this, the white characteristic was a new character acquired by the young plants which their parents had not possessed. After all, a race has got to acquire new characteristics if it is ever going to evolve.