DELIVERED AT

THE MARINE BIOLOGICAL LABORATORY

OF WOOD'S HOLL

IN THE SUMMER SESSION OF 1896

REPRINT

BOSTON, U.S.A.

PUBLISHED BY GINN & COMPANY

FIRST LECTURE.

THE VARIATIONS AND MUTATIONS OF THE

INTRODUCED SPARROW.

DOMESTICUS.

PASSER

(A SECOND CONTRIBUTION TO THE STUDY OF VARIATION.)

HERMON C. BUMPUS.

In the preface to the second volume of these Lectures it is stated that one of the leading objects of the course is "to bring forward the unsettled problems of the day, and to discuss them freely." The question of the adequacy of natural selection is one that at the present time still divides two schools of speculative biology, and is a question that can be solved only by those inductive methods which it is the function of a Biological Laboratory to suggest, adopt, and execute.

The principle of "Panmixia," or the "suspension of the preserving influence of natural selection," has formed an integral part of the speculative writings of Weismann, and, as part of his theory of "the continuity of the germ-plasm," is presumed to explain adequately the reduction of useless organs, and the occurrence, especially among domesticated animals, of "the greater number of those variations which are usually attributed to the direct influence of the external conditions of life."

This view of the regressive power of natural selection was, at the time of the original presentation of Weismann's essay ('83), not entirely new to science. Lankester ('90) calls attention to the fact that, eleven years earlier, in 1872, Darwin, in the sixth edition of the Origin of Species, had the identical principle in mind when he wrote: "If under changed conditions of life a structure before useful becomes less useful, its

diminution will be favored, for it will profit the individual not to have its nutriment wasted in building up a useless structure." Shortly after this Romanes advanced a not totally dissimilar idea in his theory of the "Cessation of Selection" (74).

In 1890 Romanes revised his earlier views, calling especial attention to the points in which they differed from those of Darwin and Weismann, and in 1895, in his posthumous work, the salient features of his theory are again indicated. Cope carried the application from structures to species when he wrote (96): "In other cases it is to be supposed that extremely favorable conditions of food, with absence of enemies, would have occurred, in which the struggle would have been nil. Degeneracy would follow this condition also."

But, without entering into the conflicting claims of originality and of priority, all the disputants are agreed that the withdrawal of the supporting influence of natural selection from an adapted organ or organism must or may, directly or indirectly, lead to a condition of degeneration. That the arguments, however, are too speculative in character is generally admitted, and there is consequently demand for inductive evidence to prove : (1) That in a specific case, and in respect to certain characters, the operation of natural selection has been suspended.

(2) That, when the operation of natural selection has been suspended, increased variation occurs.

(3) That, on the occurrence of (1) and (2), there is a departure from a previously maintained and presumably high standard, and

(4) That, unless a new equilibrium is established by adaptation to the new environment, degeneration and perhaps final elimination ensues.

It would also be of incidental interest to learn from observed facts whether the suspension of the action of natural selection. is felt immediately by an organ or organism; whether there is any indication of "self-adaptation " tending to the establishment of a new equilibrium; and whether this self-adaptation, if detected, follows one or several definite lines. Of course, if the evidence can be gathered from animals in a state of nature, and if it can be checked by a large number of examples, so much the better.