Page:The British Warblers A History with Problems of Their Lives - 9 of 9.djvu/50

 envelope in the young and the instinct to remove in the parent? By the slow accumulation of two sets of entirely separate but mutually dependent accidental variations, with nothing but elimination to determine the direction of accumulation, or by the sudden appearance of a physiological development in the young bird, plus the sudden appearance of the corresponding instinct in the parent? In a case of this description Professor Lloyd Morgan's theory of the survival of coincident variations is helpful as showing how the acquired modification can determine the survival of congenital variations in the direction of increased accommodation without biological transmission. At first small pieces of the excrement may have been occasionally swallowed for food; but supposing a small amount of intelligence had then been brought to bear upon the situation, leading to removal of part plus the occasional swallowing of part, there would have been a distinct gain to those individuals in whom such modification presented itself. Acquired accommodation would in this case have