440 KINSHIP AND ADAPTATION 



evolutionists believe that more or less modification is the 

 rule among all the descendants of a given form, and that only 

 rarely has it happened that ancestral forms have persisted 

 for ages unchanged. Thus, in regard to the last examples, 

 the most we should be willing to say is that mouse-tails were 

 probably derived from plants something hke the more primi- 

 tive forms of recent buttercups, such as the ditch crowfoot 

 (Fig. 209) ; that these ancestral crowfoots came from plants 

 something like our marsh-marigold; and so on. It is thought 

 that single traits or a few traits in comljination, are more 

 apt to survive through long periods than the many peculiari- 

 ties characterizing a complex structure. 



Closely connected with the erroneous view above men- 

 tioned is the notion that all the modern representatives of a 

 group can be arranged in a single series beginning with tlie 

 most primitive, and passing on to the most highly evolved 

 through survivals of the intermediate stages or "connecting 

 links." From what has been said it will be obvious that such 

 an arrangement would he possible only on condition that 

 all the forms which had ever appeared were actually repre- 

 sented by living descendants and that modification had 

 occurred only in one direction. As a matter of fact, gaps, 

 often great, between related forms are continually met with. 

 Indeed, if the "connecting links" of the past, represented by 

 the dead branches of our tree, had not disappeared there 

 would be no possibility of classifj'ing living forms into groups 

 and subgroups, for there could be no limits to any group. 

 Sometimes within a group it is as if Nature had as yet done 

 little or no pruning, and the result is most bewildering to those 

 who attempt a classification of the forms. No two students 

 of the group are likely to agree as to where lines of demarca- 

 tion should be drawn. Such a group is that of the roses 

 previously mentioned. But even here, for all the embarrass- 

 ing wealth of connecting links, it is quite impossible to ar- 

 range the forms in a single series. There are many diverging 

 series which branch again and again. Their relationships 

 as inferred from their degrees of likeness can best be expressed 

 by a branching system, and while of course the systematist 

 must deal with his groups one ;iftcr auoth(M' in simpl(> sequence, 



