There is thus a real risk involved in the accumulation of acquired, traditional or educational progress. Not only does it tend to abrogate or even to reverse selection, but it serves to disguise the consequences of this abrogation. If a subhuman race degenerates the fact is evident: but such a nation as our own may quite well degenerate whilst the accumulation of acquired progress, transmitted by education, almost completely cloaks the fact _for a time_. We may be congratulating ourselves upon our progress, upon our knowledge, our science and art, our institutions, legal and charitable, whilst all the time the breed is undergoing retrogression. We see now, I think, the explanation of the truth expressed by Gibbon,--“all that is human must retrograde if it do not advance.” Why should this be so? Why should it not be possible merely to maintain a position gained? The answer is that the civilisation which merely maintains its position is one in which selection has ceased: if selection had not ceased, the position would be more than maintained, there would be advance. But without selection the breed will certainly degenerate, the lower individuals multiplying more rapidly than higher ones, in accordance with Spencer's law that the higher the type of the individual the less rapidly does he multiply; and thus the race which is not advancing is retrograding, as Gibbon declared. Natural selection is the sole factor of efficient and permanent progress, but the traditional or acquired progress which we call civilisation tends to thwart or abrogate or even invert this process. I thus believe that the conditions necessary for the _secure_ ascent of any race, an ascent secured in its very blood, made stable in its very bone, have not yet been achieved in history: _and I advance this as the reason why history records no enduring Empire_. =Some historical instances.=--In the face of certain facts of contemporary history I do not for a moment assert that there are no other causes of Imperial failure than the arrest or reversal of selection. But I do assert that if this is not the cause, then, in the absence of the transmission of acquired characters, the race has not degenerated, and is capable of reasserting itself. Only by the arrest or reversal of selection can a race degenerate--apart from the racial poisons. If, then, a civilisation or Empire has fallen through causes altogether non-biological--through carelessness, or neglect of motherhood or alteration of ideals--the changes in character so produced are not transmitted to the children, and the race is not degenerate but merely deteriorated in each generation.