thousands of years, and the shortness of the period of our observations is amply counterbalanced on the one hand by the multitude of species from all parts of the organic systems which come under our notice, on the other by the immense alterations in the conditions of existence to which man submits plants and animals. How great, for instance, are the alterations in the conditions of existence which tropical plants undergo in our hot-houses and gardens! And the only alteration they show is that they are stunted and only bear blossoms with difficulty and fruits with still greater difficulty.[6] Now, if the ever-active selection principle does not produce in thousands of years even minimum alterations which can be observed, science certainly is justified in doubting for the present the asserted effect of that principle. Thus not only are the _facts_ directly opposed to the autocracy of the selection principle; but _logic_ is also none the less so. For, under the most favorable circumstances, selection would only explain the _preservation_ and perhaps also the _increase_ of useful qualities and organs, _if_ the same are already in existence and have shown themselves useful to the individual; but would not explain their _origination_. This would rather most emphatically be left to _chance_. According to the strict selection theory, it would be _pure chance_ that among the thousands and thousands of individual qualities of the individuals of a species, such qualities are always existing as offer advantages to the individual in his struggle for existence. And it would be a second series of chances, which from generation to generation would {104} have to coincide with the first, that among the individual qualities advantageous to the individual and making it victorious in the struggle for existence, there should be found always just those qualities which develop the species and raise it to a higher rank and order in the zooelogical and botanical systems. But the total of improbabilities which would have to be overcome continually in this theatre of chance, would in the course of generations necessarily amount to infinity. Thus, in the very beginning, insuperable doubts arise as to how we can explain from two causes the world of organisms which is so richly, beautifully, and systematically arranged. The first of these causes is the inclination to individual alteration, inherited indeed in the organisms, but in itself absolutely indifferent, for the systematical idea in the framework of the organic systems and for the progressive element in the development. The other is the struggle for existence and natural selection, which approaches the organisms purely from without like individual variability, must as a whole appear a necessity, but in each single case in the concrete mixture of coinciding circumstances, would seem a work of chance for the individual which is to be changed.