hybridism

[Eng. hybrid; -ism.] Biol.: The state or quality of being hybrid; hybridity. 2233 It was long believed that hybrids were uniformly sterile, and had been made so to prevent the confusion of species. Darwin ( Origin of Species , ch. ix.) combats this view, pointing out that two cla es of facts, to a great extent fundamentally different, have generally been confounded-viz., the sterility of species when first cro ed, and the sterility of the hybrids produced from them. "First cro es between forms sufficiently distinct to be ranked as species and their hybrids are very generally, but not universally, sterile. The sterility is of all degrees, and is often so slight that the most careful experiment a.. ists have arrived at diametrically opposite conclusions in ranking form a by this test. The sterility is innately variable in individuals of the same species, and is eminently susceptible to the action of favorable and unfavorable conditions. The degree of sterility does not strictly follow systematic affinity, but is governed by several curious and complex laws. It is generally different, and sometimes widely different, on reciprocal cro es between the same two species. It is not always equal in degree in a first cro , and in the hybrids produced from this cro ." -Darwin: Origin of Species (6th ed.), 262. Mr. Darwin believed that the sterility of first cro es and that of their hybrid progeny had not been effected by natural selection; had arisen from various causes. Nor, he thought, are mon grelsi. e., cro es between varieties, uniformly fertile; he considered, therefore, that there was nothing in the phenomena of hybridization to negative the view that species had first existed as var i eties.