Among special creationists today it is generally believed that basic types of organisms cannot now cross. About the past, two schools of thought exist. One holds that in the past some crossing probably occurred nearer creation week when the stocks were more "viable" and "virile" than now. The other school holds that crossing of basic types never occurred, and that our modern basic kinds have, with more or less internal variation, kept their general characteristics ever since creation week. Attention is called to the opinion of geneticists, based upon laboratory findings, that crossing of basic types has never taken place. Each basic type is visibly distinguished by its unique morphology, and the morphology of every organism is in turn determined by the specific sequence of the same two pairs of nucleotides in the DNA of the chromosomes. Dobzhansky, Lagerkvist, and Levine are quoted on this point. The unique sequence of the nucleotides in an organism's DNA determines the chemistry in its cells. Hybridization can occur only between individuals in which the chemistries of the body cells are quite similar. Such similarity occurs only among the members of the same Genesis kind. These discoveries of geneticists have shown that "viability" and "virility" have had nothing to do with the crossability of basic types of organisms. Because crossability rests wholly upon chemical compatibility (close similarity), and because such compatibility does not exist between the members of different basic types of organisms, it follows that two different basic types have never crossed. There is no known case in which two morphologically different individuals have produced a hybrid. Crossing of variants within a single basic type may result in improved stocks, and again it may result in something undesirable, such as the development of poisonous substances in the hybrid. Monkshood and guayule are cited. Because of their amenability to laboratory proof, in the study of origins two vitally important biological principles or laws are (1) Basic types (Genesis kinds, baramins) cannot cross; and (2) The Law of Limitation of Variation (Processes of variation can go no further than to produce additional variants with already existing basic types). Organic evolution and these two biological laws cannot exist on the same planet at the same time.