This numerical reduction must, however, have other consequences; it must make the germ-cells of the same individual qualitatively unlike, that is, in relation to their value in inheritance. Let us assume only four chromosomes of the rod-form ('idants') as the nuclear elements of a species, two of which, _A_ and _B_, come from the mother, and other two, _C_ and _D_, from the father, the last maturing division may, as far as we can see, result either in removing the combination _A_ and _B_ from _C_ and _D_, or _A_ and _C_ from _B_ and _D_, or _A_ and _D_ from _B_ and _C_; there is thus a possibility of one of six different combinations of rods in any one germ-cell. What is the same thing, six different kinds of germ-cells differing in their hereditary primary constituents may _be developed in the same_ individual. As this new combination, or, as we may call it, neotaxis of the germ-plasm elements, takes place in female as well as in male individuals, there is a possibility that, in fertilization, 6 × 6 = 36 individuals with different primary constituents may arise from the germ-cells of the same two parents. Of course the number of possible combinations increases very considerably in proportion to the normal number of rods, for with eight of these it comes up to 70, and with sixteen to 12,870; the number of individuals differing in their inherited primary constituents would thus be enormous, for each of the 70 or of the 12,870 different hereditary minglings of the ovum could combine in amphimixis with 70 or 12,870 different sperm-cells, so that 70 × 70 and 12,870 × 12,870 offspring individually different in their primary constituents might arise from the same two parents. In Man there are said to be sixteen nuclear rods; so that in his case the last-mentioned number of parental hereditary minglings might occur. This may seem a disproportionately high number as compared with the small number of children of a human pair, but we must not judge from the case of Man alone, and in plants and animals, which we have already discussed, the number of descendants is very much larger, and is often enormous. We saw what significance this apparent extravagance on the part of nature has, for without it adaptation to changed conditions of life would not be possible, since, if only so many were born as could attain to reproduction, no selection of the fittest could take place. The same would be the case if all the young of a species were alike, and even if all the descendants of a single pair were alike, effective selection would be excluded, since only as many individualities could be selected as there were pairs of parents. It is easy to understand that selection works more effectively the larger the number of descendants of a species and the more they differ from each other. The chance that the best possible combination of characters will occur is thereby increased.