Page:Popular Science Monthly Volume 67.djvu/66

60 will never become established. Cases of this sort, in which a species continually gives off mutations, that can not survive, and yet continue to appear, are known.

In most cases the survival of a species is not determined by one particular character, but by the sum total of all. Therefore since the characters mutate independently, we might expect to find occasionally in a new species some characters more perfect than the actual requirements demand; other characters less perfect than is necessary to maintain the species if survival depended on these alone, and many characters that suffice for the demands of survival. Thus in man, to take but a single example, the ear and the eye may be more perfectly developed in some respects than the demands of survival require, while the appendix vermiformis is actually injurious to the welfare of the race. The majority of the peculiarities lie somewhere between these extremes. A new race of men can not be produced by selection of those individuals that show fluctuating variations in these different directions, but must arise by the sudden appearance of a new type or types, which, finding a foothold, may establish themselves along side of the present races. It may be that definite variations are even at present occurring, but are not of sufficient importance or difference to attract attention. Permanent improvement must be looked for in this direction, and not from the picking out of those individuals that fluctuate in an advantageous direction.

If we take the position that the creation of new forms is not the outcome of a long continued process of remodeling of each species, but that new forms appear 'spontaneously,' how can we account for the adaptation of new species to their environment? Are we to believe that all new forms that appear from 'inner causes' will be already adapted to some external set of conditions? A very slight familiarity with living things will give, I believe, a negative answer to this question. Nevertheless let us not conclude too quickly that none of the new forms will be adapted to some environment, even if some of them are not.

Darwin defined natural selection as follows: 'This preservation of favorable individual differences and variations, and the destruction of those which are injurious, I have called natural selection, or the