THE EVOLUTION OF LIVING BEINGS. II9 



the history of the earth, than he has. His production 

 may have been, what is usually, called the result of ^ 

 chance e. g. of the meeting and mating of two forms, 

 at that particular moment and not at an earlier onej^_ 

 just as the moment of the birth of children depends, 

 in the last instance, on the chance meeting of the man 

 and woman who, after this meeting, decide to marry. 



In how far chance, in this sense, has played a role 

 in successive evolution is an unanswerable question; ^ 

 could man f. i. have originated from gametes, pro- 

 duced by two particular reptils, if these had happened 

 to mate, or is a shortening of the sequence : reptils — 

 „lower" mammals — man, impossible? 



We know not; and the so-called Biogenetisches 

 Grundgesetz gives no solution either, although it ra- 

 ther points towards the possibility of shortening. 



All this is speculation ; we have anyhow not to deal 

 with the question in which other way evolution might 

 have taken place, but how it has taken place and this 

 we can deduce from the geological record only, 

 which shows clearly that it took place successively. 



With such a successive evolution, our theory that 

 new Linneons arise from a cross of preexisting ones, is 

 in full accord, so that the moment has come to consider 

 the evidence for the occurrence of crossing of different 

 Linneons in nature. 



