Part 169. Sudden adaptations. Professor Hugo de Vries, an eminent botanist of Amsterdam, Holland, was led to a new view of the process of evolution by studying for a number of years the descendants of some large-flowered evening primroses which had been imported from America and had escaped from a garden near his home into a neighboring field where they grew in great profusion. Among these escaped plants De Vries found a large amount of fluctuating variation in every part, and frequent abnormalities, but what especially attracted his attention was the appearance of two well-characterized forms which he recognized at once as new to science. One of these was distinguished by a short style and no stamens, while the other was peculiar in having smooth leaves of particularly beautiful appearance. Each was represented at first by only a few specimens confined to a particular part of the field as if derived from the seeds of single plant. These three forms were found to come true to seed and when crossed the seedlings were like one parent or the other; or occasionally other new forms were produced, with or without crossing, which were as unlike the parent form as were the two new forms first discovered. In the course of seven generations several such new forms appeared, numbering in individuals about eight hundred out of a total of about fifty thousand plants raised. Similar forms also appeared in the field. All these new forms were distinct types differing from one another in several particulars such as shape and color of leaves, flowers or fruit, and annual, biennial, or perennial habit; and although growing together they did not intergrade. They were thus as sharply definable as species are, and they could be regarded as true species except for the fact that their differences distinguished parent from offspring. De Vries regarded them as elementary species equivalent to what botanists have been calling well-marked varieties, races, or subspecies, and as representing the abrupt changes through the accumulation of which species and higher groups arise. He calls variations of this sort mutations,1 the new forms being termed mutants. Hence we may designate as mutationism this new theory of evolutionary change.

1 Mu-ta'tion - L. mutatio, a changing.

Mutationism supposes that from time to time, especially under the influence of changed conditions, some of the individuals of a species bear offspring distinctly different from the parent, often in several particulars, and that the set of peculiarities thus suddenly arising is completely hereditary even when individuals of the new form are crossed with other forms of the same species. That is to say, the progeny from parents of two different mutations are like one or the other parent, and never intermediate as is often the case with crosses between fluctuating variations. If mutations again mutate and we have mutants of the second or higher degree, their hybrids may be wholly like one parent or the other, or may be apparently intermediate from having inherited one or more peculiarities from one parent and the rest from the other; but such cases of apparently intermediate forms show new combinations of elements rather than elements of an intermediate sort, each element being always hereditary unless it gives place to a new element through mutation. While the parent form may continue to be inherited unchanged by certain descendants for innumerable generations the descendants of a mutation to which it has given rise may mutate again and again, until finally a form has arisen characterized by so many new elements that it is no longer capable of producing offspring like those of the original ancestral form. Then a new species has appeared; and by a similar differentiation through many successive mutations, there would arise genera, families, and groups of higher order.

Whether the peculiarities of a mutation are beneficial or not is immaterial provided only they do not unfit the organism for living under the conditions where it occurs. If it can gain a foothold either in the same environment as that of its parent or under some other set of conditions a new race or new species may be started. It has been commonly assumed by naturalists that every slightest peculiarity of an organism must have some important relation to its welfare whether apparent to us or not, since otherwise we could not understand its fitting into the environment under which it thrives. On this view we should have to suppose that all the peculiarities of the new forms of escaped primroses represent sudden adaptations; but in that case it must be admitted that very diverse adaptations fit about equally well into the same environment. The assumption that every trait must be connected with some use, seems, however, to be quite gratuitous. This supposition is not at all necessary to the theory of mutations, although, as we have seen, it is a necessary incumbrance to the theory of natural selection. On the new view we may suppose that a mutation presents features which may be more or less beneficial, indifferent, or even more or less injurious; yet if it gets into an environment which permits such a form to live, then the traits of each description may become characteristic of a surviving group. We all know that however useless or undesirable defects or bad habits may be, they are not necessarily fatal, and are sometimes perpetuated. Thus we can account for the fact that many characters of the highest systematic importance seem to have nothing whatever to do with utility.

Yet, we know that many organs do serve marvelously well the needs of the organism. There is no reason, however, why their adaptive features may not have arisen through mutations, even without selection, and we have seen that initial stages in the development of many an adaptation are of so little use that selection could not reasonably be supposed to act on them. At the same time it is of course not impossible in other cases that natural selection may operate under certain conditions now and then occurring. Variations of the mutative sort would then serve especially well as steps in the process of species-making, because of the way in which they are inherited, while fluctuating variations might also sometimes contribute to the result, provided incompatible features did not arise as mutations. For the most part, however, selection may now be supposed to play only a subordinate role in organic evolution, its effects showing chiefly in the maintenance of a certain standard of perfection in an established type. A plant grows where it can, and it can grow at all only by having the chance, and being fit to take advantage of it. When we have said this we have expressed about all that it is necessary to admit of the doctrine of natural selection. We must remember also that selection has at best but a negative value; it cannot originate anything, it can only favor certain individuals by weeding out others. As to mutations, the reader has doubtless already become aware of their striking likeness to "special creations."

If it could be shown that acquired characters may be passed over from one mutation to another, we might suppose that a direct influence of the environment is instrumental in originating species. We know that it does control individual peculiarities often in a striking way, and may not improbably account for the constant appearance of features sometimes attributed to other causes. The great difficulty often is to decide which of several possible causes may have brought about a given result; and only long continued, careful experiments can give a satisfactory answer. So far as we may judge from such extended observations as those of Dr. Sturtevant and others, the direct effects of external agencies like the effects of selection are confined to modifying types rather than originating them.

Those of my readers who have played with a kaleidoscope will remember that as the cylinder is moved slowly forward or back gradual changes in the design take place, and any favorite arrangement may be recovered by simply moving the cylinder back to the place where that arrangement appeared,-all this being possible so long as the cylinder does not move beyond a certain point; for if it gets ever so little beyond that point there is a sudden rearrangement of the elements thereby forming an entirely new design, which may in turn be modified as before by restricted changes of position. The gradual modification of the design within definite limits is like the modification of a type as effected by fluctuating variations or acquired characters; the sudden change is like a mutation upsetting the previous equilibrium and establishing a new equilibrium which is not at all disturbed by vacillating modifications.