The Discovery of Natural Selection 



lead to very imperfect and erroneous conclusions. . . . 

 The following propositions in Organic Geography and 

 Geology give the main facts on which the hypothesis [see 

 p. 96] is founded. 



Geography 



(1) Large groups, such as classes and orders, are 

 generally spread over the whole eartli, while smaller ones, 

 such as families and genera, are frequently confined to 

 one portion, often to a very limited district. 



(2) In widely distributed families the genera are often 

 limited in range ; in widely distributed genera, well-marked 

 groups of species are peculiar to each geographical dis- 

 trict. 



(3) When a group is confined to one district and is rich 

 in species, it is almost invariably the case that the most 

 closely allied species are found in the same locality or in 

 closely adjoining localities, and that therefore the natural 

 sequence of the species by affinity is also geographical. 



(4) In countries of a similar climate, but separated by 

 a wide sea or lofty mountains, the families, genera and 

 species of the one are often represented by closely allied 

 families, genera and species peculiar to the other. 



Geology 



(5) The distribution of the organic world in time is very 

 similar to its present distribution in space. 



(6) Most of the larger and some of the smaller groups 

 extend through several geological periods. 



(7) In each period, however, there are peculiar groups, 

 found nowhere else, and extending through one or several 

 formations. 



(8) Species of one genus, or genera of one family, occur- 

 ring in the same geological time are more closely allied than 

 those separated in time. 



(9) As generally in geography no species or genus occurs 

 in two very distant localities without being also found in 

 intermediate places, so in geology the life of a species or 

 genus has not been interrupted. In other words, no group 

 or species has come into existence twice. 



95 



