Page:Popular Science Monthly Volume 48.djvu/696

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from ears with many rows, and that the greater the number of rows on the ear from which the seed is taken the smaller is the number of ears produced with a small number of rows. It is also plain that, as the number of rows on the ear from which the seed was taken increases, the number of ears produced with a large number of rows increases, and that we have in each case a very considerable number of ears which equal their parents and a few which excel them, even when the parent seeds are far beyond the maximum for all ordinary corn. Fritz Müller says he has never, under ordinary conditions, except in three instances, found an ear with more than eighteen rows, and Darwin puts the maximum at twenty rows; yet we have among the children of seed from a twenty-two-rowed ear no less than 4·8 per cent, or eighteen ears out of 373 with twenty rows, and one ear out of 373 with twenty-six rows, and it will also be seen that the number of children which equal their parents increases in each case in each successive generation.

Thus the seed planted in 1867 from an eighteen-rowed ear produced 12·6 per cent of eighteen-rowed children. The eighteen-rowed ear planted in 1868 from an eighteen-rowed parent produced 18·2 per cent of eighteen-rowed children, and the eighteen-rowed seed planted in 1869 from eighteen-rowed parents and grandparents produced 18·6 per cent of eighteen-rowed children. The series is 12·6 per cent, 18·2 per cent, and 18·6 per cent.

The rapid change which took place in the "type" after only three years of selection is well shown by the following table, which gives the dominant number of rows at each sowing, and also the percentage of ears which had this number:

1867, 12 rows 48 per cent. 1868, 14 rows 35·4 per cent.
1867, 14 " 48·6 " 1869, 14 " 37·3 "
1868, 14 " 48·5 " 1869, 16 " 41·6 "
1867, 14 " 37·8 " 1869, 16 " 41·8 "

The minimum for the third generation is equal to the mean for the first; the mean for the third generation, sixteen rows, is very near the maximum for ordinary corn, and the maximum for the third generation is far beyond the maximum for the grandparents, and much beyond the maximum for the parents.

No one can dispute the well-known fact that this sort of pedigree selection for a single point quickly grows less and less effective, and soon reaches a maximum; but this is no proof of any "principle of organic stability," or anything else except the truth that long ages of natural selection have made the organism such a unit or coordinated whole that no great and continuous change in one feature is possible, unless it is accompanied by general or constitutional change.