138 THE EVOLUTION OF LIVING BEINGS. 



identical constitution derive from hybrids or from spe- 

 cifically pure individuals. 



Consequently, we may confidently expect to meet oc- 

 casionally very similar human individuals, who are 

 not al all related in the usual sense, and we all know 

 that this happens so frequently, that it is even said 

 that each man has his duplicate somewhere. 



What value then have we to ascribe to the blood- 

 test of UHLENHUTH and NUTTALL? 



No other, than revealing, perhaps, similarity of con- 

 stitution, which is quite another thing than relati- 

 onship. 



As little as the result of testing for Ca in chemistry, 

 revealing the presence of this element in the stalactites 

 of a grotto and in the substance of our bones, reveals 

 the derivation of the calcium in the stalactitesjand in our 

 bones from the same source much less the deriva- 

 tion of the stalactites and of ourselves from the same 

 source as little the results of the bloodtest reveal 

 relationship. Yet, in a sense, it is correct, that species are 

 related to one another in a similar way as human bro- 

 thers or cousins are, viz in as much, as this expresses the 

 fact that both are segregates from a former cross. 



In the case of brothers and cousins, we can trace 

 their origin if there is a family register, if no such re- 

 gister of births exists, we can not; so that, if species are 

 really ,,related" in a similar way, it is, in the absence 

 of species-birth registers, a priory improbable that we 

 shall ever be able to reconstruct their phylogeny. 



