Page:Popular Science Monthly Volume 18.djvu/116

106 proper to industrial life; and that, so long as these two modes of life, utterly alien in their natures, have to be jointly carried on, there will continue this jumbling of the regulative systems they respectively require.

The second of the objections above noted, as needing to be otherwise dealt with than by further explanation of the formula of evolution, concerns the increase of likeness among developing systems of civil law; in proof of which increase of likeness Mr. Leslie quotes Sir Henry Maine to the effect that "all laws, however dissimilar in their infancy, tend to resemble each other in their maturity": the implication to which Mr. Leslie draws attention being, that in respect of their laws societies become not more heterogeneous but more homogeneous. Now, though in their details systems of law will, I think, be found to acquire, as they evolve, an increasing number of differences from one another, yet in their cardinal traits it is probably true that they usually approximate. How far this militates against the formula of evolution we shall best see by first considering the analogy furnished by animal organisms. Low down in the animal kingdom there are simple mollusks with but rudimentary nervous systems—a ganglion or two and a few fibers. Diverging from this low type we have the great sub-kingdom constituted by the higher mollusca and the still greater sub-kingdom constituted by the vertebrata. As these two types evolve, their nervous systems develop; and though in the highest members of the two they remain otherwise unlike, yet they approximate in so far that each acquires great nervous centers: the large cephalopods have clustered ganglia which simulate brains. Compare, again, the mollusca and the articulata in respect of their vascular systems. Fundamentally unlike as these are originally, and remaining unlike as they do throughout many successive stages of ascent in these two sub-kingdoms, they nevertheless are made similar in the highest forms of both by each having a central propelling organ—a heart. Now, in these and in some cases which the external organs furnish, such as the remarkable resemblance evolution has produced between the eyes of the highest mollusca and those of the vertebrata, it may be said that there is implied a change toward homogeneity. No zoologist, however, would admit that these facts really conflict with the general law of organic evolution. As already explained, the tendency to progress from homogeneity to heterogeneity is not intrinsic but extrinsic. Structures become unlike in consequence of unlike exposures to incident forces. This is so with organisms as wholes, which, as they multiply and spread, are ever falling into new sets of conditions; and it is so with the parts of each organism. These pass from primitive likeness into unlikeness as fast as the mode of life places them in different relations to actions—primarily external and secondarily internal; and with each successive change in mode of life new unlikenesses are superposed. One of the implications is that, if in organisms otherwise different there arise like sets of conditions to which certain parts