Page:Popular Science Monthly Volume 68.djvu/489

Rh influence of artificial selection a non-adaptive or indifferent character becomes adaptive or selective. Among those animals or plants which submit readily to domestication almost any natural species, distinguished by non-adaptive characters, could be reproduced with all its traits by a process of carefully controlled selective breeding.

It has long been known that individual fluctuations of an extreme degree sometimes occur, and that these may be to a degree persistent in heredity. Of such nature was the Ancon sheep, the iceberg blackberry and numerous other races or forms known in the domestication of animals or the cultivation of plants. The generally normal structure of such individuals distinguishes them from monstrosities, which are usually freaks of development rather than of heredity.

The name 'saltation,' or in recent years 'mutation,' has been applied to extreme fluctuation, the immediate cause of which is unknown. The experiments of Dr. Hugo de Vries on the saltations of the descendants of an American form of evening primrose (Œnothera lamarckiana) have recently drawn general attention again to the possibility that saltation has had a large part in the process of formation of species. As to this it may be said that the possible variation within each species is much greater than the range of the individuals which actually survive. The condition of domestication favors the development of extreme variation, because such individuals may be preserved from interbreeding with the mass, and they may survive even if their characters are unfavorable to competition in the struggle for existence. Among plants it is noticed that new soil and new conditions seem to favor large variation in the progeny, although the traits thus produced are rarely if ever hereditary. Cases more or less analogous to those noted by Dr. de Vries are not rare in horticulture. The cross-breeding of variant forms favors the appearance of new forms. Among actual species in a state of nature, there are very few which seem likely to have arisen by a sudden leap or mutation. The past and the future of de Vries's evening primroses are yet to be shown, and it is not at all unlikely that the original Œnothera lamarckiana found in a field near Amsterdam was a hybrid stock, a product of the florist, the behavior of its progeny being not unlike that which appears in the progeny of hybrids. The species called by de Vries Œnothera lamarckiana is not known in its wild state anywhere in North America, the parent region of the species of evening primrose or Œnothera. It is, moreover, known that the seeds of hybrids of an American species, probably Œnothera biennis, the common evening primrose, with other