168 



The Journal of Heredity 



Zealand and many other groups gave 

 the same result, showing that the law 

 is quite general. Other authors have 

 contributed analogous data for the 

 grasses of Australia, for the endemics 

 of the Bahama Islands and other cases. 

 Everywhere the statistical method, just 

 described, conduces to the same con- 

 clusions. 



In stating the rule in a general way, 

 some restrictions will, of course, be 

 found to be necessary. For this rea- 

 son I wish to quote the most recent 

 expression of these as given by the 

 author : "The area occupied at any 

 given time, in any given country, by 

 any group of allied species at least 

 ten in number depends chiefly, so long 

 as conditions remain reasonably con- 

 stant, upon the ages of the species of 

 that group in that country, but may be 

 enormously modified by the presence 

 of barriers such as seas, rivers, moun- 

 tains, changes of climate from one 

 region to the next, or other ecological 

 boundaries, and the like, also by the 

 action of man, and by other causes." 



The main point in this contention is. 

 that the species have to be considered 

 in small groups of allied forms. If 

 single species are studied, the distribu- 

 tion will of course depend upon many 

 factors which, however, cancel one an- 

 other as soon as the statistical method 

 is applied to them. Among these fac- 

 tors the most prominent are given by 

 the means of dispersal, acclimatisation, 

 suitability to the society of plants in 

 which a species may find itself, barriers 

 of all kinds, whether physical, climatic 

 or ecological, individual habit of the 

 species itself, and so on. Rut these 

 factors will be different for the in- 

 dividual s]:)ecies. whereas age works on 

 all of them in the same sense. 



Or in other words, while the posses- 

 sion of a good mechanism for dispersal 

 mav be of great advantage to a plant, 

 es])ecially in reaching areas that are 

 only a small distance away, it is by no 

 means essential for world-wide distri- 

 bution. 



Origin of Species and Natural 

 Selection 



On the basis of these statistical re- 

 sults the theory of the origin of species 

 by means of natural selection of in- 

 finitesimal variations is subjected to a 

 severe criticism. As a rule, the rate of 

 dispersion of new species is indepen- 

 dent of their special organizations, since 

 it is the same for all of them. In the 

 largest number of endemic species 

 there are simply no adaptations to the 

 local conditions. The new forms in- 

 herit their suitability to their environ- 

 ment from their ancestors, without any 

 appreciable change or improvement. 

 The systematical characters, which con- 

 stitute them as good Linnean species, 

 do not show any regular relation to 

 their struggle for life. Considered 

 from a biological point of view these 

 new qualities are of very secondary 

 importance. 



From these considerations some very 

 valuable deductions may be derived. 

 It goes without saying that any new 

 forms which should not, from the very 

 beginning, be sufficiently adapted to 

 the prevailing conditions of life, will 

 soon be wiped out. But whenever the 

 adaptation is the same as that of the 

 ancestors, the chance of survival will 

 also be the same. The new forms will 

 develop and spread beside the older 

 ones, and according to the same general 

 law. There is no reason for assuming 

 a further competition between the spe- 

 cies, even if the struggle be sharp be- 

 tween the individuals themselves. The 

 struggle for life, which took so promi- 

 nent a place in the older theories con- 

 cerning the evolution of the species, 

 seems to be reduced to the very first 

 period after their origin. New forms 

 have not to conquer their ancestors in 

 order to supplant them, nor to extir- 

 pate them in order to secure their 

 jilaces in the flora for themselves. The 

 older species may simply continue their 

 spreading beside their derivatives. Some 

 of them may, of course, die out in the 

 process, but this will be rather an ex- 



