Page:Popular Science Monthly Volume 63.djvu/225

Rh It would be impossible to have any such compound as ABCD, but we should get instead one of the four character-combinations AC, AD, BC, BD. The inheritance of a single character from one grandparent would certify the inheritance of all, and thus establish an alibi for the other ancestor of the same side of the house. What a resource for genealogists to be able to prove that a man was no relative of his grandfather, or even that he had no consanguinity with his own brother! Alas that Mendel and other 'experimental evolutionists' have proved that inheritance is by characters and not by chromosomes, if these behave as Professor Wilson indicates. Only the so-called monohybrids, those differing by a single character, would tolerate such an interpretation, and the fallacy of it is obvious as soon as we remember that hybrids may be assembled with reference to two, three or more characters derived from different ancestors. Moreover, Professor Spillman has recently drawn from his experiments with wheat concrete and detailed examples of the fact that definite proportions of such combinations are permanent, since two dominant characters do not antagonize each other. Unless it be in the case where the varieties crossed differ in but a single character we know of a certainty that the germ-cells are not of pure descent with respect to parentage. The most that can be claimed is that they are organized reciprocally with reference to the divergent parental characters, since it seems that the different features may be distributed and recombined quite without reference to the manner in which they were grouped in the parents. In his hybrid wheats Professor Spillman finds all the combinations possible under the mathematical theory of chance. How this could be managed by the chromosomes our cytological friends may be able to conjecture, though from the outside it looks like a rather difficult question.

Hybridization is possible only between groups of common origin, and the characters which show the Mendelian effect are those on which the greatest divergence has taken place. That such characters may be changed about or substituted, and are able to enter freely into all varieties of combination, not only does not prove that the chromosomes are mechanisms of heredity, but it greatly decreases the probability of mechanical theories of evolution, since it shows the facility with which characters may be accumulated in normal interbreeding, before the Mendelian degree of divergence has been reached.

If two plants different in other respects are found to differ also in