564 CHAPTERS ON EVOLUTION. 



" it is, further, probable that no part of the body is exempt from the 

 second source of impairment ; that, namely, which consists in the 

 natural death or deterioration of the parts (independent of the death 

 and decay of the whole body) after a certain period of their life. It 

 may be proved, partly by demonstration, and partly by analogy, that 

 each integral or elemental part of the body is formed for a certain 

 natural period of existence in the ordinary conditions of active life, 

 at the end of which period, if not previously destroyed by outward 

 force or exercise, it degenerates and is absorbed, or dies and is cast 

 out ; needing, in either case, to be replaced for the maintenance of 

 health." To these weighty words we may lastly add the opinion of 

 Dr. Carpenter, who remarks that, " when the adult type has once 

 been completely attained, every subsequent change is one rather of 

 degeneration than of development, of retrogression rather than of 

 advance." 



Degeneration is thus an invariable concomitant of life. So far 

 from being in any way an abnormal phase of living action, it is seen 

 to be as natural a process for living beings to retrogress wholly, as 

 we have seen in some cases, or partly in others as it is for them to 

 develop and advance. And what is thus undoubtedly true of the 

 individual man or other animal, is no less so of the race. " Buried 

 civilisations " are by no means unknown ; extinct culture is an archaeo- 

 logical fact; the decline and fall of nations is matter of history. 

 May not these things be likewise explained as a part of that wide 

 theory of life which regards even the highest interests of man as 

 lying within the operation and sway of causes which mould his 

 physical organisation ? If this notion be accepted, then is the idea 

 of degeneration as a normal phase of life rendered still more feasible 

 and plain. Reaching to the individual and to the species as well ; 

 extending and including in its scope the lowly organised as well as 

 the higher being ; affecting one group or class lightly, and influencing 

 another well-nigh to the complete exclusion of progress, we find 

 degeneration and retrogression to be numbered among the stern 

 realities of existence. And no less clearly and forcibly may we trace 

 the truly natural place of degeneration in our own physical history : 

 since, as physiology teaches and daily experience declares, not an 

 action is wrought or a thought conceived without the presence of 

 change and decay of tissue a process this which, limited in early 

 life by progressive growth and by development, at last comes in our 

 latter days to assume the reins of government, and in time to dissipate 

 our energy and substance into the nothingness of physical and 

 corporate extinction. 



The philosophy of biology, however, may, in conclusion, be found 

 to point out to us that the subject of degeneration, whilst treating of 

 a powerful factor in modifying the living form, yet possesses a 



