Early Theories. A number of erroneous ideas about heredity date to ancient times. They were discredited only in the last few centuries.

The theory that living organisms were produced from nonliving matter by spontaneous generation received a setback through the work of the French bacteriologist Louis Pasteur (1822-1895). At one time it was thought that human beings could be born of other mammals. The belief that certain cereal plants could turn into others was held as late as the middle of the 20th century by some Russian horticulturists.

For centuries people believed in “blood inheritance,” a blending of bloods in half-and-half portions from the parents, quarter portions from grandparents, and so on. The notion persists in remarks about persons inheriting good or bad blood.

The theory of acquired characteristics was introduced by the ancient Greeks. According to this theory, traits acquired by an organism during its lifetime can be passed on to its offspring. For example, a man who developed his muscles by exercise would have children with strong muscles. This theory was supported by the French biologist Jean Baptiste Lamarck (1744-1829). It was officially approved in 1948 by the Communist party in the Soviet Union and did not lose favor with the party for several years. Intensive research in the early half of the 20th century by the United States biologist Theodosius Dobzhansky has helped to discredit the theory of acquired characteristics.

Mendel's work was neglected until 1900, when his principles were rediscovered by three biologists working independently: Karl E. Correns, in Germany; Hugo de Vries, in the Netherlands; and Erich Tschermak, in Austria. Mendel's papers were republished, and his findings became the basis for the science of genetics.