SPECULATIVE ZOOLOGY. lg7 



possible that they are not in the direct line of descent at all. The 

 evidence is entirely circumstantial and indefinite, and it is impossible 

 to show that any of the reptile-like birds which have been discovered 

 have any descendants at the present day. All we can say is that, 

 if our birds are not their descendants, it is very probable that they 

 are the descendants of some other unknown form very much like 

 them. 



At the best it is simply a question of probability, not of direct 

 proof, and paleontological evidence is never definite enough to enable 

 us to reach a specific conclusion which may not possibly be wrong, and, 

 this being the state of the case, we may fairly ask whether such specu- 

 lations upon probability, in the absence of direct evidence, are entitled 

 to be called science. In order to answer this question, and to show 

 that phylogenetic speculation may be strictly within the legitimate 

 scope of science, we will make use of an imaginary illustration. 



Suppose that a large continental area, which is inhabited by a homo- 

 geneous human race, is invaded by a band of settlers from another 

 country, about as the first European settlers forced themselves upon 

 the homogeneous inhabitants of the United States. 



Suppose that these settlers, increasing in numbers, gradually spread 

 over the whole country, interbreeding with the autochthones, until, in 

 later generations, the population comes to consist of two equally dis- 

 tributed races, represented by individuals of pure descent, with strongly 

 marked race-characteristics ; and, in addition to these, a great number 

 of hybrids, presenting the characteristics of the two pure races in all 

 degrees and manners of union. 



As time goes on, imagine this latter class to increase at the expense 

 of the others, until few persons of pure blood are left ; and meanwhile 

 suppose that a number of persons of a third race are introduced, about 

 as the negroes were introduced into this country, and, after this immi- 

 gration has lasted for a time, suppose it to stop, and let this third race 

 spread and increase, and, after a time, gradually mix with the other 

 two. Let the same process take place again, until the population comes 

 to be made up of four quite dissimilar races with well-marked race- 

 characteristics, crossed in such a way that no individuals of the origi- 

 nal race or of the first immigration are of perfectly pure blood, while 

 there are a few nearly pure types of the third race, and still more of 

 the fourth. Suppose, now, that an anthropologist undertakes to study 

 the inhabitants of the country in order to learn what he can of their 

 origin and history, and let him begin by attempting to classify them. 

 Any attempt to divide them up into groups will fail, on account of 

 the complexity of their relationships ; and, although there are traces 

 of four types, it is not possible to arrange them in four classes, since 

 most of them have resemblances to more than one type. After long 

 study of their relationships, and an enumeration of all the forms which 

 are distinguishable, we may suppose him to hit upon some such expe- 



