CHAPTER XI 

 KINSHIP AND ADAPTATION 



163. The problem of origins. Kinship among living 

 things implies a common origin. We kno^v that kin always 

 resemble one another more or less closely, and this likeness 

 we attribute to their inheriting similar features from the 

 same ancestor. Two individuals which differ from each 

 other no more than do offspring of the same parents, we re- 

 gard as belonging to tlie same species; and because of such 

 likeness among the memliers of a species we feel sure of their 

 having descended fi'om an original ancestor or ancestors 

 which had essentially the same characteristics. 



No one doul)ts that all the kidney-boan plants in the world 

 are the descendants of a plant or plants having the charac- 

 teristic features of a kidney-bean; but, as we have seen, 

 there are numerous varieties of this species which differ 

 strikingly from one another, often more widely than do man\' 

 species of the same genus. Why then maj^ not all the species 

 of beans be descended from a nrore remote ancestor, and so 

 be as truly akin as the members of one species? And if the 

 species of this genus are thus related why not also, though in 

 less degree, the genera of the pulse family, the families of the 

 rose order, the orders of the case-seed class, the classes of the 

 seedwort branch, the Ijranches of the vegetable kingdom, and, 

 indeed, all grou])s of plants and animals according to their 

 several degrees of resemblance? Why may it not be true that 

 a natural system of classification expresses kinsliip? 



To some readers it ma>' ai:)pear profitless to ]iursue in- 

 quiries so remote, and they naturalh' ask, How can we know 

 or why should we care al)out the origin of living things? Our 

 answer must be that while of course we cannot know about 

 this absolutely, we may Ix' mor(^ or less sure that our conclu- 



-12S 



