5 oo POPULAR SCIENCE MONTHLY 



while in still deeper water is a golden-yellow form, the original 

 Cephalopholis fulvus. Similar relation of olive and red forms, or of 

 black and yellow types, has been noticed in other groups of fishes. 



In similar fashion, it is claimed that within the species lines of 

 segregation may be set up on a physiological basis those of a certain 

 type not breeding freely with those of other types. This theory is 

 largely hypothetical. It is conceivably true under certain circum- 

 stances, but there is little evidence that any particular species has 

 originated in that way. 



It is beyond question that differences greater than those ordinarily 

 separating distinct species may be produced by continuous conscious 

 0/ unconscious selection on the part of man. To what extent these 

 breeds would retain their characters under the leveling processes of 

 nature, it is impossible to say in any particular case. On the other 

 hand, in the nature of things, all of them are of very much more 

 recent origin than competing species in nature. While it may be that 

 no wild species has originated from human selection, it is true, on the 

 other hand, that the races thus produced are the same in essence as the 

 subspecies and species produced in nature. The same forces are at 

 work, the basis of selection only being altered by man. The river flows 

 according to the same laws over a natural ledge of rock or over an 

 artificial dam. 



Hybridization, as above shown, may produce species as well marked 

 and as fertile as any natural species. But no wild species is known 

 to have arisen from this cause, unless we regard the warbler, Helmin- 

 thophaga leucobronchialis, as an established species. 



A saltation or mutation, beginning with an individual, may extend 

 its characteristics to a numerous progeny, thus forming the beginning 

 of a species. But while this influence may in theory, or even in fact, 

 have a large importance, it is not likely that many species originate in 

 this way. There is no clear evidence that any wild species known to us 

 has arisen from a sudden large individual variation or mutation. 



Orthogenesis 



A large number of unexplained, but apparently related, phenomena 

 have been recorded under the name of determinate variation, or have 

 been grouped together as examples of a process to which Eimer has 

 applied the name of Orthogenesis. 



Setting theory aside, these cases are essentially of this character. 

 In geological times a certain number of genera appear, each one in 

 a certain direction farther along than its predecessor. Very often a 

 certain organ will be progressively more and more highly developed 

 until a certain point, when it is progressively degraded or simplified 

 in its structure. Examples of this are found among the ammonites, or 

 cephalopods with coiled shells, the chambers in the cell elaborately 



