How it began
Gregor Mendel was an Augustinian friar and teacher at the monastery in Brünn, now Brno. From 1854 to 1856 he tested 34 varieties of pea to make sure their traits bred true. He then crossed varieties that differed in seven traits, such as plant height and seed color, and counted the offspring. He presented his results in two lectures to the Natural Science Society in Brünn in 1865, and the society published his paper, "Experiments on Plant Hybrids," in its journal in 1866.
Before it existed
Earlier authorities had observed that the offspring of fertile hybrids tended to revert to the parent species, and they concluded that hybridization could not multiply species. Heredity was widely pictured as a blending of the parents' traits. Darwinian evolution was assumed to rest mainly on the selection of small, blending variations.
How it works
In the first generation of hybrids one form of a trait, the dominant, appeared and the other, the recessive, was hidden. In the next generation the recessive form returned, and dominant and recessive plants appeared in a ratio very close to 3 to 1. Mendel reasoned that a hybrid forms germ cells carrying one form or the other, the principle later called the law of segregation. Crosses with two and three traits showed that the traits were passed on independently of one another.
How it spread
In 1900 three botanists, Hugo de Vries in the Netherlands, Carl Correns in Germany and Erich Tschermak von Seysenegg in Austria, independently reported results from hybrid experiments similar to Mendel's. Their reports brought his paper to general notice decades after his death.
Who pushed back
The paper drew little attention. Readers took it as a more exact demonstration of what was already assumed about hybrids and missed its wider meaning. The Swiss botanist Karl Wilhelm von Nägeli corresponded with Mendel but stayed skeptical, and Mendel did little to publicize his work. After the rediscovery, those who championed Mendel met opposition from Darwinians, because his traits did not blend.
What lasted
Britannica describes Mendel as the first person to lay the mathematical foundation of the science of genetics, in what came to be called Mendelism. His principles are known as the law of segregation, the law of dominance and the law of independent assortment. Later work on genes linked on chromosomes showed limits to independent assortment, but the principles remain the starting point of the field.
