Page:Popular Science Monthly Volume 62.djvu/496

490 it might as well be possible that the mutations were many-sided, but that of them only those survived which excelled their ancestors in a particular direction, better fitting them for the existing conditions.

Finally one can come to a very important conclusion in regards the manner in which plants and animals mutate. It is this, that new species did not originate in a single individual, but in a number of individuals, either at the same time or during a number of years. Delboeuf was the first to formulate this idea, and Scott and others agree with him on this point.

This is a quite simple and natural view to take. A single individual would, among all the members of his former species, practically have no chance of life and reproduction, even if it were a hermaphrodite plant and much better adapted to local conditions than the others. For this chance plays too prominent a part in the struggle for life. There are a thousand chances that a seed does not germinate or is killed in its prime, independent of any qualities it may possess. Once the young plant has passed this period, the chances certainly are better, but even then many succumb because they occupy an unfavorable place. But when a plant produces a number of individuals of the new species at the same time, and repeats this for a number of years, then the chances of the new species are sufficient; and this even if it is weaker or in some regards inferior, and certainly if it is as good as the mother species. It is not at all necessary that the new species be stronger, or be at once offered the opportunity to make use of its superior qualities. Delboeuf carefully calculated the chances, but even without these calculations one can see the truth of his remarks. For the larger the number of mutating individuals, and the more generations this mutating lasts, the greater will become the chance of the new species to maintain itself among the old one, always supposing the former is not so weak as to be crowded out each time. To be better equipped than others before entering upon the struggle for life is certainly a great advantage, but not a sine quâ non for ultimate success.

Reviewing the above, we find that the mutation theory comprises the following theses. Species originated from others by sudden but small changes, often so small as to be hardly visible to the neophyte. They are constant and true to seed from the first; neither are they connected with the mother species by a series of intermediate forms, nor do they have to pass in their prime, a stage of gradual development. This formation of new forms does not take place continually, but it is only from time to time that a species enters a period of mutability; in this case it produces, during a certain number of years, one or more, perhaps an exceedingly large number of new species. The mother species itself remains unchanged; it may persist after the