Cu.vr. V. LAWS OF VARIATION. IO7 



ciiArxER y. 



LAWS OF VAUIATIOX. 



Effects of clmntrofl Coiuiillont'—T'iJo and Dis>nso, combined with Natural Selection; 

 Orirtiiii (if Fliirlit and of Vision— Acclimatization— Correlated Variatiou— Com- 

 pensation and Keonoiny of (imwtli— False C:orrclation» — Mnlti|)le, Uudinicntary, 

 and l.iiwly-or^'anized Stnietuies< variable— Parts developed in an Unusual Man- 

 ner are hij;ldy variable : ?>poeific Characters more variable ttwn Generic: Second- 

 ary Sexual characters variable— Species of the t^anic Genus vary in au analoguua 

 llauucr— Ueverbioua to long-lost Charactera — Sumaiary. 



. I HAVE hitherto sometimes spoken as if the variations — so 

 comn'ion and multilorin with org'anic beings nnder domestication, 

 and in a lesser degree with those in a state of nature — had 

 l)een due to cliance. This, of course, is a wholly incorrect ex- 

 pression, but it serves to acknowledge plainly our ignorance 

 of the cause of each particular variation. Some authors be- 

 lieve it to be as much the function of the reproductive system 

 to produce individual difTerences, or slight deviations of struc- 

 tuie, as to make the child like its parents. But the fact of 

 variations and monstrosities occurring much more frequently 

 under domestication than under Nature, and the greater varia- 

 l>ility of species having wide ranges than of those having re- 

 stricted ranges, lead to the conclusion that variability is directly 

 related to the conditions of life to Avhich each species has been 

 exposed during several successive generations. In the first 

 cliapter I attempt(>d to show that changed conditions act in 

 two ways, directly on the whole organization or on certain 

 ])ar(s alone, jind indirectly through the reproductive sj'stcm. 

 Jn all cases th(M-e ate two factors, the nature of the organism, 

 which is nuich the most important of the two, and the nature 

 of the conditions. The direct acticm of changed conditions, 

 leads to (h'Tmite or indefinite results. In the latter case the 

 organization seems to become plastic, and we have nnich fluc- 

 tuating variability. In the former case the nature of the or- 

 ganism is such that it yields readily, when subjected to cer- 

 lain conditions, and all, or nearly all the individuals become 

 modified in the same way. 



