Alfred Russel Wallace 



(10) The following law may be deduced from these facts : 

 Every species has come into existence coincident hoth in time 

 and space with a pre-existing closely allied species. 



This law agrees with, explains and illustrates all the 

 facts connected with the following branches of the sub- 

 ject : 1st, the system of natural affinities ; 2nd, the dis- 

 tribution of animals and plants in space; 3rd, the same 

 in time, including all the phenomena of representative 

 groups, and those which Vx^. Forbes supposed to mani- 

 fest polarity; 4th, the phenomena of rudimentary organs. 

 We will briefly endeavour to show its bearing upon each 

 of these. 



If [this] law be true, it follows that the natural series 

 of affinities will also represent the order in which the 

 several species came into existence, each one having had 

 for its immediate antetype a clearly allied species exist- 

 ing at the time of its origin. ... If two or more species 

 have been independently formed on the plan of a common 

 antetype, then the series of affinities will be compound, 

 and can only be represented by a forked or many-branched 

 line. . . . Sometimes the series of affinities can be well re- 

 presented for a space by a direct progression from species 

 to species or from group to group, but it is generally found 

 impossible so to continue. There constantly occur two or 

 more modifications of an organ or modifications of two 

 distinct organs, leading us on to two distinct series of 

 species, which at length differ so much from each other 

 as to form distinct genera or families. These are the 

 parallel series or representative groups of naturalists, and 

 they often occur in different countries, or are found fossil 

 in different formations. . . . We thus see how difficult it 

 is to determine in every case whether a given relation is 

 an analogy or an affinity, for it is evident that as we go 

 back along the parallel or divergent series, towards the 

 common antetype, the analogy which existed between the 

 two groups becomes an affinity. . . . Again, if we consider 

 that we have only the fragments of this vast system, the 

 stems and main branches being represented by extinct 

 species of which we have no knowledge, while a vast mass 



