Page - 155 - in The Origin of Species

CORRELATED VARIATION 155 kidney-bean has been often cited for a similar purpose, and with much greater weight; but until someone will sow,'dur- ing a score of generations, his kidney-beans so early that a very large proportion are destroyed by frost, and then collect seed from the few survivors, with care to prevent accidental crosses, and then again get seed from these seedlings, with the same precautions, the experiment cannot be said to have been tried. Nor let it be supposed that differences in the con- stitution of seedling kidney-beans never appear, for an ac- count has been published how much more hardy some seed- lings are than others; and of this fact I have myself ob- served striking instances. On the whole, we may conclude that habit, or use and disuse, have, in some cases, played a considerable part in the modification of the constitution and structure ; but that the effects have often been largely combined with, and some- times overmastered by, the natural selection of innate variations. CORRELATED VARIATION I mean by this expression that the whole organisation is so tied together during its growth and development, that when slight variations in any one part occur, and are accu- mulated through natural selection, other parts become modi- fied. This is a very important subject, most imperfectly understood, and no doubt wholly dift'ercnt classes of facts may be here easily confounded together. We shall presently see that simple inheritance often gives the false appearance of correlation. One of the most obvious real cases is, that variations of structure arising in the young or larvre nat- urally tend to affect the structure of the mature animal. The several parts of the body which are homologous, and which, at an early embryonic period, are identical in struc-_ ture, and which are necessarily exposed to similar condi- tions, seem eminently liable to vary in a like manner: we see this in the right and left sides of the body varying in the same manner; in the front and hind legs, and even in the jaws and limbs, varying together, for the lower jaw is be- lieved by some anatomists to be homologous with the limbs. These tendencies, I do not doubt, may be mastered more or