Page:The Effect of External Influences upon Development.djvu/21
Effect of External Influence upon Development
personal selection, and not by intra-selection. The value of the principle of intra-selection does not seem to me, however, to be diminished on this account: it still remains of the very greatest importance, for without it no higher organism could either persist or exist, or even possibly have become developed. For were this not so, the organism would be formed from the egg much in the same way as a building would be constructed every stone of which was prepared before the site or the neighbourhood in which it was to be erected had been chosen, or even the use to which it would be put had been decided upon. Such an ontogeny, predetermined in every detail, would no more produce an organism fit for life, than—as Roux has aptly put it—would a commander be victorious, who, instead of giving general instructions to his chief officers as to the placing and movements of their troops, should in advance issue detailed orders for the conduct of every one down to the lieutenants, or even to each private soldier. The influences which encounter organisms during their development are never exactly similar, and to adapt themselves to these the organisms must have a certain amount freedom.
These influences, moreover, are by no means purely of an external kind, but are to a great extent exercised by one part of the organism on another, by cell on cell, by tissue on tissue, by organ on organ. If I am not mistaken, the phenomenon which Darwin described as correlation, and justly regarded as an important factor in evolution, is for the most part an effect of intra-selection, which has great influence on phylogeny