The Application of Statistical Methods and Experiments to the Ideas of Heredity. Mendel.—This feature of investigating questions of heredity is of growing importance. The first to complete experiments and to investigate heredity to any purpose was the Austrian monk Mendel (1822-1884) (Fig. 95), the abbot of a monastery at Brünn. In his garden he made many experiments upon the inheritance, particularly in peas, of color and of form; and through these experiments he demonstrated a law of inheritance which bids fair to be one of the great biological discoveries of the nineteenth century. He published his papers in 1866 and 1867, but since the minds of naturalists at that time were very much occupied with the questions of organic evolution, raised through the publications of Darwin, the ideas of Mendel attracted very little attention. The principles that he established were re-discovered in 1900 by De Vries and other botanists, and thus naturalists were led to look up the work of Mendel.
Fig. 95.—Gregor Mendel, 1822-1884.
Permission of Professor Bateson.
The great discovery of Mendel may be called that of the purity of the germ-cells. By cross-fertilization of pure breeds of peas of different colors and shapes he obtained hybrids. The hybrid embodied the characteristics of the crossed peas; one of the characteristics appearing, and the other being held in abeyance—present within the organization of the pea, but not visible. When peas of different color were cross-fertilized, one color would be stronger apparently than the other, and would stand out in the hybrids. This was called the dominant color. The other, which was held in abeyance, was called recessive; for, though unseen, it was still present within the young seeds. That the recessive color was not blotted out was clearly shown by raising a crop from the hybrid, a condition under which they would produce seeds like those of the two original forms, and in equal number; and thereafter the descendants of these peas would breed true. This so-called purity of the germ-cells, then, may be expressed in this way: "The hybrid, whatever its own character, produces ripe germ-cells, which produce only the pure character of one parent or of the other" (Castle).
Although Mendel's discovery was for a long time overlooked, happily the facts were re-discovered, and at the present time extensive experiments are being made with animals to test this law: experiments in the inheritance of poultry, the inheritance of fur in guinea-pigs, of erectness in the ears of rabbits, etc., etc. In this country the experiments of Castle, Davenport, and others with animals tend to support Mendel's conclusion and lift it to the position of a law.
Rank of Mendel's Discovery.—The discovery by Mendel of alternative inheritance will rank as one of the greatest discoveries in the study of heredity. The fact that in cross-breeding the parental qualities are not blended, but that they retain their individuality in the offspring, has many possible practical applications both in horticulture and in the breeding of animals. The germ-cells of the hybrids have the dominant and the recessive characters about equally divided; this will appear in the progeny of the second generation, and the races, when once separated, may be made to breed true.
Mendel's name was not recognized as a prominent one in the annals of biological history until the re-discovery of his law in 1900; but now he is accorded high rank. It may be remarked in passing that the three leading names in the development of the theories of heredity are those of Mendel, Galton, and Weismann.
